Re: Put UICollectionView within UITableViewCell

[Glen Huang]

I’ll give it a shot, thank you very much

> On 10 Mar 2018, at 10:27 AM, Cosmo Birch  wrote:
> 
> But you presumably know the width (i.e. the CollectionView width minus any 
> insets), and you can calculate the height based on that with NSString or 
> NSAttributedString boundingRect functions. Assuming you have a subclass for 
> your CollectionViewCell, you can add a method to return your cell height 
> based on its contents layout.
> 
>> On Mar 9, 2018, at 8:21 AM, Gary L. Wade  
>> wrote:
>> 
>> @Cosmo
>> 
>> My collection items contain label, so I don’t know the exact sizes before 
>> hand.
>> 
> 
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Re: Put UICollectionView within UITableViewCell

[Cosmo Birch]

But you presumably know the width (i.e. the CollectionView width minus any 
insets), and you can calculate the height based on that with NSString or 
NSAttributedString boundingRect functions. Assuming you have a subclass for 
your CollectionViewCell, you can add a method to return your cell height based 
on its contents layout.

> On Mar 9, 2018, at 8:21 AM, Gary L. Wade  wrote:
> 
> @Cosmo
> 
> My collection items contain label, so I don’t know the exact sizes before 
> hand.
> 

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Re: Put UICollectionView within UITableViewCell

[Glen Huang]

@Cosmo

My collection items contain label, so I don’t know the exact sizes before hand.

@Gary

In my case I actually also need to display section headers and section index 
titles, so using just a collection view probably won’t be easy I guess.

—

From the suggestions it seems it might be something very difficult to pull off. 
I wonder if anyone ever reverse-engineered multiline UILabels to see how table 
cells can have correct heights containing them.

> On 10 Mar 2018, at 12:14 AM, Cosmo Birch <minonom...@gmail.com> wrote:
> 
> Where I work we have spent a fair amount of trying unsuccessfully to get 
> self-sizing collection view cells to work as described by Apple documentation 
> with UICollectionViews that have any sort of complexity. I would suggest 
> trying to implement the sizeForItemAtIndexPath delegate method to see if that 
> solves your problem. Sorry if the name of the method is slightly off. I can’t 
> look it up at the moment.
> 
>> On Mar 9, 2018, at 8:00 AM, Glen Huang <hey...@gmail.com> wrote:
>> 
>> Hi,
>> 
>> I asked a question about putting UICollectionView within UITableViewCell on 
>> Apple Developer Forums (https://forums.developer.apple.com/thread/98176), 
>> but it doesn’t get many replies. I’m not sure if it’s ok to repost the 
>> question here. I apologize if it’s not.
>> 
>> Here is the question:
>> 
>> Hi, I'm trying to create a table view with cell content like this
>> 
>> | Label |  
>> | CollectionItem 1   CollectionItem 2  CollectionItem 3 |  
>> | CollectionItem 4  |  
>> 
>> Collection view item should auto wrap at cell end, both the collection view 
>> and table view use automatic height.
>> 
>> I can somewhat achieve this effect by doing:
>> put the label and the collection view in a vertical stack view, make the 
>> stack view's each edge touch table cell's corresponding edge.
>> disable collection view scrolling.
>> collection view's intrinsicContentSize returns layout's 
>> collectionViewContentSize value.
>> in table cell's prepareForReuse method, I make the collection view reload 
>> its data.
>> 
>> But the problem comes when each table cell can contain different number of 
>> collection items: some table view cells have incorrect heights, clipping its 
>> collection view. My guess is that when table cells get reused, they don't 
>> take collection view's new intrinsicContentSize into account.
>> 
>> I tried calling sizeToFit/layoutIfNeeded/updateConstraints in cell's 
>> prepareForReuse method, none of them works.
>> 
>> If I replace the collection view with a multiline label, and make each cell 
>> contain different length of text, the cells all have correct heights.
>> 
>> I wonder why label are able to correctly resize cells? how can I make 
>> collection views do the same?
>> 
> 

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Re: Put UICollectionView within UITableViewCell

[Gary L. Wade]

I would suggest rethinking the table view enclosure and just use a collection 
view with headers and footers by way of the supplemental views.
--
Gary L. Wade
http://www.garywade.com/

> On Mar 9, 2018, at 8:00 AM, Glen Huang <hey...@gmail.com> wrote:
> 
> Hi,
> 
> I asked a question about putting UICollectionView within UITableViewCell on 
> Apple Developer Forums (https://forums.developer.apple.com/thread/98176), but 
> it doesn’t get many replies. I’m not sure if it’s ok to repost the question 
> here. I apologize if it’s not.
> 
> Here is the question:
> 
> Hi, I'm trying to create a table view with cell content like this
> 
> | Label |  
> | CollectionItem 1   CollectionItem 2  CollectionItem 3 |  
> | CollectionItem 4  |  
> 
> Collection view item should auto wrap at cell end, both the collection view 
> and table view use automatic height.
> 
> I can somewhat achieve this effect by doing:
> put the label and the collection view in a vertical stack view, make the 
> stack view's each edge touch table cell's corresponding edge.
> disable collection view scrolling.
> collection view's intrinsicContentSize returns layout's 
> collectionViewContentSize value.
> in table cell's prepareForReuse method, I make the collection view reload its 
> data.
> 
> But the problem comes when each table cell can contain different number of 
> collection items: some table view cells have incorrect heights, clipping its 
> collection view. My guess is that when table cells get reused, they don't 
> take collection view's new intrinsicContentSize into account.
> 
> I tried calling sizeToFit/layoutIfNeeded/updateConstraints in cell's 
> prepareForReuse method, none of them works.
> 
> If I replace the collection view with a multiline label, and make each cell 
> contain different length of text, the cells all have correct heights.
> 
> I wonder why label are able to correctly resize cells? how can I make 
> collection views do the same?
> 
> Thanks very much.
> 

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Re: Put UICollectionView within UITableViewCell

[Cosmo Birch]

Where I work we have spent a fair amount of trying unsuccessfully to get 
self-sizing collection view cells to work as described by Apple documentation 
with UICollectionViews that have any sort of complexity. I would suggest trying 
to implement the sizeForItemAtIndexPath delegate method to see if that solves 
your problem. Sorry if the name of the method is slightly off. I can’t look it 
up at the moment.

> On Mar 9, 2018, at 8:00 AM, Glen Huang <hey...@gmail.com> wrote:
> 
> Hi,
> 
> I asked a question about putting UICollectionView within UITableViewCell on 
> Apple Developer Forums (https://forums.developer.apple.com/thread/98176), but 
> it doesn’t get many replies. I’m not sure if it’s ok to repost the question 
> here. I apologize if it’s not.
> 
> Here is the question:
> 
> Hi, I'm trying to create a table view with cell content like this
> 
> | Label |  
> | CollectionItem 1   CollectionItem 2  CollectionItem 3 |  
> | CollectionItem 4  |  
> 
> Collection view item should auto wrap at cell end, both the collection view 
> and table view use automatic height.
> 
> I can somewhat achieve this effect by doing:
> put the label and the collection view in a vertical stack view, make the 
> stack view's each edge touch table cell's corresponding edge.
> disable collection view scrolling.
> collection view's intrinsicContentSize returns layout's 
> collectionViewContentSize value.
> in table cell's prepareForReuse method, I make the collection view reload its 
> data.
> 
> But the problem comes when each table cell can contain different number of 
> collection items: some table view cells have incorrect heights, clipping its 
> collection view. My guess is that when table cells get reused, they don't 
> take collection view's new intrinsicContentSize into account.
> 
> I tried calling sizeToFit/layoutIfNeeded/updateConstraints in cell's 
> prepareForReuse method, none of them works.
> 
> If I replace the collection view with a multiline label, and make each cell 
> contain different length of text, the cells all have correct heights.
> 
> I wonder why label are able to correctly resize cells? how can I make 
> collection views do the same?
> 

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Put UICollectionView within UITableViewCell

[Glen Huang]

Hi,

I asked a question about putting UICollectionView within UITableViewCell on 
Apple Developer Forums (https://forums.developer.apple.com/thread/98176), but 
it doesn’t get many replies. I’m not sure if it’s ok to repost the question 
here. I apologize if it’s not.

Here is the question:

Hi, I'm trying to create a table view with cell content like this
 
| Label |  
| CollectionItem 1   CollectionItem 2  CollectionItem 3 |  
| CollectionItem 4  |  

Collection view item should auto wrap at cell end, both the collection view and 
table view use automatic height.
 
I can somewhat achieve this effect by doing:
put the label and the collection view in a vertical stack view, make the stack 
view's each edge touch table cell's corresponding edge.
disable collection view scrolling.
collection view's intrinsicContentSize returns layout's 
collectionViewContentSize value.
in table cell's prepareForReuse method, I make the collection view reload its 
data.
 
But the problem comes when each table cell can contain different number of 
collection items: some table view cells have incorrect heights, clipping its 
collection view. My guess is that when table cells get reused, they don't take 
collection view's new intrinsicContentSize into account.
 
I tried calling sizeToFit/layoutIfNeeded/updateConstraints in cell's 
prepareForReuse method, none of them works.
 
If I replace the collection view with a multiline label, and make each cell 
contain different length of text, the cells all have correct heights.
 
I wonder why label are able to correctly resize cells? how can I make 
collection views do the same?
 
Thanks very much.
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UICollectionView cells sometimes drawn on top of section header

[Steve Christensen]

iOS 10.

I'm seeing some odd behavior where occasionally collection view cells are drawn 
on top of their section header view instead of behind it. When I use the view 
inspector in Xcode then I do, in fact, see the cells in front of the section 
header.

These are pretty generic cells that contain an image. The only thing special is 
that the image is loaded asynchronously and then set on the cells UIImageView 
in a completion block on the main thread.

Has anybody else run across this behavior before?


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Re: UICollectionView Moving

[Luke Hiesterman]

UICollectionView doesn’t know that your layout is conceptually columns, so when 
a section is empty, it has no concept of what space is appropriate to drop 
items into an empty section. You need to help it out by overriding the 
following method on your layout:

- (NSIndexPath *)targetIndexPathForInteractivelyMovingItem:(NSIndexPath 
*)previousIndexPath withPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);

Luke

On Mar 9, 2016, at 5:58 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

Ok - I think this is the final question.

I've created a layout that is essentially a bunch of ragged bottom columns - 
like a Trello or Kanban board. The items in the collection view are "stories" 
with size around 100x100. To begin with, I prepopulate the underlying datastore 
and things are great, I've got 2, 3 or 4 stories in each column. Dragging 
around works just as expected.

In my case, a column is a SECTION. A 4 column board then has 4 sections.

Problem: if I move ALL the items out of a column (a column is a SECTION) ... I 
can't move anything back INTO the column (section). I don't think the SECTION 
has any HEIGHT if it has no items ... and consequently, dragging a "story" item 
over the area that represents a column does nothing because the CollectionView 
doesn't actually create anything there if I have at 0 item layoutAttributes for 
that section.

Is there a specific way to do this? I still have a supplementary view as the 
column header and it always appears ... and in a UITableView, I think, if I 
have a empty section but have a section header, the built in move functionality 
will allow me to drag an item over the section header and allow me to drop into 
the section (but I can't remember if this is true) --- but dragging an "story" 
item over the supplementary view does nothing.

In the worst case, do I need to keep some sort of hidden item as the first 
element? I take all "stories" out of a column (section), should I put at least 
one, invisible item in the column (section) to keep it available as a drag 
target?

Hope that makes sense - I tend to be wordy.

Thanks,
-Luther



On Tue, Mar 8, 2016 at 12:05 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:
Now we're cooking with GAS!!!

override func applyLayoutAttributes(layoutAttributes: 
UICollectionViewLayoutAttributes) {
print("apply layout attributes!: \(titleLabel.text)")
}

Thanks Man!
-Luther



On Mon, Mar 7, 2016 at 11:54 PM, Luke Hiesterman 
<luket...@apple.com<mailto:luket...@apple.com>> wrote:
By teaching a cell to respond to an attribute I merely meant that it should 
override setLayoutAttributes: and do something in there with the relevant 
property. Hope that helps.

Luke

On Mar 7, 2016, at 9:39 PM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

> teach your cell classes to respond to that property

Want to think about this out loud. Wondering what would 'trigger' a lookup on 
the layout's layoutAttributesForItemAtIndexPath ... and where would I store the 
indexPath I am dragging around.

If I were to be more literal - in my view controller, I handle the 
UIGestureRecognizerState.Began event. At this point, I can get the indexPath of 
the element I am about to move and if I change something on that cell at that 
time, it sticks for the life of the drag without reference to layoutAttributes. 
I also handle the UIGestureRecognizerState.Changed event and again, if I 
retrieve the cell at the gesture's locationInView and change things in it ... 
those changes stick until I let go of the drag.

Stepping into the custom layout for a minute ... as you suggested, I am now 
implementing layoutAttributesForInteractivelyMovingItemAtIndexPath ... and that 
is getting invoked in response to the updateInteractiveMovementTargetPosition 
call I am making as the gesture location changes. Now, I know the collection 
view's methods are triggering the layout's callbacks - but I'm not sure what 
would trigger me to fetch the custom attributes you are suggesting. At a 
minimum, to ask the layout for the attributes at that indexPath, I'd have to 
actually be tracking the 'selectedIndexPath' in which case, I could just get 
the cell and modify it directly.

I guess I'm wondering how to "teach my cells classes to respond to that 
property" ... Cells are reused so I'm not even sure how I'd go about setting up 
and tearing down a KVO type relationship for the specific cell I am dragging 
around. Maybe there is a WWDC video that digs into this? or it's an easy 
explain?

Sorry for being so long-winded. I'm not sure I'm communicating my question 
well. Hope you can understand my underlying question and nudge me the right way 
but at any rate, thanks for your help so far. I'd love to use an elegant, "made 
for CollectionView" solution ... but I

Re: UICollectionView Moving

[Luther Baker]

That was it. Thanks Luke!

Really digging this control ...

On Wed, Mar 9, 2016 at 10:36 AM, Luke Hiesterman <luket...@apple.com> wrote:

> UICollectionView doesn’t know that your layout is conceptually columns, so
> when a section is empty, it has no concept of what space is appropriate to
> drop items into an empty section. You need to help it out by overriding the
> following method on your layout:
>
> - (NSIndexPath *)targetIndexPathForInteractivelyMovingItem:(NSIndexPath
> *)previousIndexPath withPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);
>
> Luke
>
> On Mar 9, 2016, at 5:58 AM, Luther Baker <lutherba...@gmail.com> wrote:
>
> Ok - I think this is the final question.
>
> I've created a layout that is essentially a bunch of ragged bottom columns
> - like a Trello or Kanban board. The items in the collection view are
> "stories" with size around 100x100. To begin with, I prepopulate the
> underlying datastore and things are great, I've got 2, 3 or 4 stories in
> each column. Dragging around works just as expected.
>
> In my case, a column is a SECTION. A 4 column board then has 4 sections.
>
> Problem: if I move ALL the items out of a column (a column is a SECTION)
> ... I can't move anything back INTO the column (section). I don't think the
> SECTION has any HEIGHT if it has no items ... and consequently, dragging a
> "story" item over the area that represents a column does nothing because
> the CollectionView doesn't actually create anything there if I have at 0
> item layoutAttributes for that section.
>
> Is there a specific way to do this? I still have a supplementary view as
> the column header and it always appears ... and in a UITableView, I think,
> if I have a empty section but have a section header, the built in move
> functionality will allow me to drag an item over the section header and
> allow me to drop into the section (but I can't remember if this is true)
> --- but dragging an "story" item over the supplementary view does nothing.
>
> In the worst case, do I need to keep some sort of hidden item as the first
> element? I take all "stories" out of a column (section), should I put at
> least one, invisible item in the column (section) to keep it available as a
> drag target?
>
> Hope that makes sense - I tend to be wordy.
>
> Thanks,
> -Luther
>
>
>
> On Tue, Mar 8, 2016 at 12:05 AM, Luther Baker <lutherba...@gmail.com>
> wrote:
>
>> Now we're cooking with GAS!!!
>>
>> override func applyLayoutAttributes(layoutAttributes:
>> UICollectionViewLayoutAttributes) {
>> print("apply layout attributes!: \(titleLabel.text)")
>> }
>>
>> Thanks Man!
>> -Luther
>>
>>
>>
>> On Mon, Mar 7, 2016 at 11:54 PM, Luke Hiesterman <luket...@apple.com>
>> wrote:
>>
>>> By teaching a cell to respond to an attribute I merely meant that it
>>> should override setLayoutAttributes: and do something in there with the
>>> relevant property. Hope that helps.
>>>
>>> Luke
>>>
>>> On Mar 7, 2016, at 9:39 PM, Luther Baker <lutherba...@gmail.com> wrote:
>>>
>>> > teach your cell classes to respond to that property
>>>
>>> Want to think about this out loud. Wondering what would 'trigger' a
>>> lookup on the layout's layoutAttributesForItemAtIndexPath ... and where
>>> would I store the indexPath I am dragging around.
>>>
>>> If I were to be more literal - in my view controller, I handle the
>>> UIGestureRecognizerState.Began event. At this point, I can get the
>>> indexPath of the element I am about to move and if I change something on
>>> that cell at that time, it sticks for the life of the drag without
>>> reference to layoutAttributes. I also handle the
>>> UIGestureRecognizerState.Changed event and again, if I retrieve the cell at
>>> the gesture's locationInView and change things in it ... those changes
>>> stick until I let go of the drag.
>>>
>>> Stepping into the custom layout for a minute ... as you suggested, I am
>>> now implementing layoutAttributesForInteractivelyMovingItemAtIndexPath ...
>>> and that is getting invoked in response to the
>>> updateInteractiveMovementTargetPosition call I am making as the gesture
>>> location changes. Now, I know the collection view's methods are triggering
>>> the layout's callbacks - but I'm not sure what would trigger me to fetch
>>> the custom attributes you are suggesting. At a minimum, to ask the layout
>>> for the attributes at that indexPath, I'd have to 

Re: UICollectionView Moving

[Luther Baker]

 change it (or does it not require
>> the delegates or datasources ... ?)
>>
>> Thanks,
>> -Luther
>>
>>
>>
>> On Mon, Mar 7, 2016 at 2:45 PM, Luke Hiesterman <luket...@apple.com>
>> wrote:
>>
>>> You can create your own subclass of UICollectionViewLayoutAttributes and
>>> add something like an “isMoving” property to that. Then teach your cell
>>> classes to respond to that property by changing the background color.
>>>
>>> Luke
>>>
>>> On Mar 7, 2016, at 11:44 AM, Luther Baker <lutherba...@gmail.com> wrote:
>>>
>>> Thanks Luke! That was it - I can drag and drop successfully now.
>>>
>>> One more question, how do I modify a property of the item I'm dragging
>>> around if the property is NOT currently in UICollectionViewLayoutAttributes
>>> ... I don't see a call to the datasource or delegate when I select the cell
>>> for moving ... so I'm not sure how to change the background color to "red"
>>> for instance.
>>>
>>> Would I have to add my own view to the superview and manually move it
>>> around in the dragging callbacks?
>>>
>>> Thanks!
>>> -Luther
>>>
>>>
>>> On Mon, Mar 7, 2016 at 11:59 AM, Luke Hiesterman <luket...@apple.com>
>>> wrote:
>>>
>>>> I’d check your return value for this method in your layout:
>>>>
>>>> - (UICollectionViewLayoutAttributes
>>>> *)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath
>>>> *)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);
>>>>
>>>> Luke
>>>>
>>>> On Mar 7, 2016, at 9:55 AM, Luther Baker <lutherba...@gmail.com> wrote:
>>>>
>>>> I followed the directions here,
>>>>
>>>> http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
>>>> - to add iOS9 style dragging to my UICollectionView - and it sort of
>>>> works.
>>>>
>>>> As described in the article, I added a long press gesture recognizer and
>>>> wired it in to make calls on the collection view -- but now, if I long
>>>> press, the element under my finger disappears. As I drag the transparent
>>>> image around, the other elements shift - but I can never see the
>>>> element I
>>>> am dragging around. When I let go, there is simply a hole left where I
>>>> "dropped" the element.
>>>>
>>>> I do, very much, have a custom layout and I'm not sure that if, for
>>>> drag, I
>>>> need to do anything special. Do I need to calculate the frame of the
>>>> item I
>>>> am dragging around? I'm not sure what to try next except to roll my own
>>>> dragging. Any thoughts or things to try?
>>>>
>>>> Thanks in advance.
>>>> ___
>>>>
>>>> Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
>>>>
>>>> Please do not post admin requests or moderator comments to the list.
>>>> Contact the moderators at cocoa-dev-admins(at)lists.apple.com
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>>>>
>>>>
>>>>
>>>
>>>
>>
>
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Re: UICollectionView Moving

[Luther Baker]

Now we're cooking with GAS!!!

override func applyLayoutAttributes(layoutAttributes:
UICollectionViewLayoutAttributes) {
print("apply layout attributes!: \(titleLabel.text)")
}

Thanks Man!
-Luther



On Mon, Mar 7, 2016 at 11:54 PM, Luke Hiesterman <luket...@apple.com> wrote:

> By teaching a cell to respond to an attribute I merely meant that it
> should override setLayoutAttributes: and do something in there with the
> relevant property. Hope that helps.
>
> Luke
>
> On Mar 7, 2016, at 9:39 PM, Luther Baker <lutherba...@gmail.com> wrote:
>
> > teach your cell classes to respond to that property
>
> Want to think about this out loud. Wondering what would 'trigger' a lookup
> on the layout's layoutAttributesForItemAtIndexPath ... and where would I
> store the indexPath I am dragging around.
>
> If I were to be more literal - in my view controller, I handle the
> UIGestureRecognizerState.Began event. At this point, I can get the
> indexPath of the element I am about to move and if I change something on
> that cell at that time, it sticks for the life of the drag without
> reference to layoutAttributes. I also handle the
> UIGestureRecognizerState.Changed event and again, if I retrieve the cell at
> the gesture's locationInView and change things in it ... those changes
> stick until I let go of the drag.
>
> Stepping into the custom layout for a minute ... as you suggested, I am
> now implementing layoutAttributesForInteractivelyMovingItemAtIndexPath ...
> and that is getting invoked in response to the
> updateInteractiveMovementTargetPosition call I am making as the gesture
> location changes. Now, I know the collection view's methods are triggering
> the layout's callbacks - but I'm not sure what would trigger me to fetch
> the custom attributes you are suggesting. At a minimum, to ask the layout
> for the attributes at that indexPath, I'd have to actually be tracking the
> 'selectedIndexPath' in which case, I could just get the cell and modify it
> directly.
>
> I guess I'm wondering how to "teach my cells classes to respond to that
> property" ... Cells are reused so I'm not even sure how I'd go about
> setting up and tearing down a KVO type relationship for the specific cell I
> am dragging around. Maybe there is a WWDC video that digs into this? or
> it's an easy explain?
>
> Sorry for being so long-winded. I'm not sure I'm communicating my question
> well. Hope you can understand my underlying question and nudge me the right
> way but at any rate, thanks for your help so far. I'd love to use an
> elegant, "made for CollectionView" solution ... but I don't think I'm
> looking at it correctly yet. Just in general I guess, how can a change to
> the layoutAttributes cause my CollectionViewDelegate and DataSources to
> fetch the cell I'm dragging around and change it (or does it not require
> the delegates or datasources ... ?)
>
> Thanks,
> -Luther
>
>
>
> On Mon, Mar 7, 2016 at 2:45 PM, Luke Hiesterman <luket...@apple.com>
> wrote:
>
>> You can create your own subclass of UICollectionViewLayoutAttributes and
>> add something like an “isMoving” property to that. Then teach your cell
>> classes to respond to that property by changing the background color.
>>
>> Luke
>>
>> On Mar 7, 2016, at 11:44 AM, Luther Baker <lutherba...@gmail.com> wrote:
>>
>> Thanks Luke! That was it - I can drag and drop successfully now.
>>
>> One more question, how do I modify a property of the item I'm dragging
>> around if the property is NOT currently in UICollectionViewLayoutAttributes
>> ... I don't see a call to the datasource or delegate when I select the cell
>> for moving ... so I'm not sure how to change the background color to "red"
>> for instance.
>>
>> Would I have to add my own view to the superview and manually move it
>> around in the dragging callbacks?
>>
>> Thanks!
>> -Luther
>>
>>
>> On Mon, Mar 7, 2016 at 11:59 AM, Luke Hiesterman <luket...@apple.com>
>> wrote:
>>
>>> I’d check your return value for this method in your layout:
>>>
>>> - (UICollectionViewLayoutAttributes
>>> *)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath
>>> *)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);
>>>
>>> Luke
>>>
>>> On Mar 7, 2016, at 9:55 AM, Luther Baker <lutherba...@gmail.com> wrote:
>>>
>>> I followed the directions here,
>>>
>>> http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
>>> - to add iOS9 style dragging

Re: UICollectionView Moving

[Luke Hiesterman]

By teaching a cell to respond to an attribute I merely meant that it should 
override setLayoutAttributes: and do something in there with the relevant 
property. Hope that helps.

Luke

On Mar 7, 2016, at 9:39 PM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

> teach your cell classes to respond to that property

Want to think about this out loud. Wondering what would 'trigger' a lookup on 
the layout's layoutAttributesForItemAtIndexPath ... and where would I store the 
indexPath I am dragging around.

If I were to be more literal - in my view controller, I handle the 
UIGestureRecognizerState.Began event. At this point, I can get the indexPath of 
the element I am about to move and if I change something on that cell at that 
time, it sticks for the life of the drag without reference to layoutAttributes. 
I also handle the UIGestureRecognizerState.Changed event and again, if I 
retrieve the cell at the gesture's locationInView and change things in it ... 
those changes stick until I let go of the drag.

Stepping into the custom layout for a minute ... as you suggested, I am now 
implementing layoutAttributesForInteractivelyMovingItemAtIndexPath ... and that 
is getting invoked in response to the updateInteractiveMovementTargetPosition 
call I am making as the gesture location changes. Now, I know the collection 
view's methods are triggering the layout's callbacks - but I'm not sure what 
would trigger me to fetch the custom attributes you are suggesting. At a 
minimum, to ask the layout for the attributes at that indexPath, I'd have to 
actually be tracking the 'selectedIndexPath' in which case, I could just get 
the cell and modify it directly.

I guess I'm wondering how to "teach my cells classes to respond to that 
property" ... Cells are reused so I'm not even sure how I'd go about setting up 
and tearing down a KVO type relationship for the specific cell I am dragging 
around. Maybe there is a WWDC video that digs into this? or it's an easy 
explain?

Sorry for being so long-winded. I'm not sure I'm communicating my question 
well. Hope you can understand my underlying question and nudge me the right way 
but at any rate, thanks for your help so far. I'd love to use an elegant, "made 
for CollectionView" solution ... but I don't think I'm looking at it correctly 
yet. Just in general I guess, how can a change to the layoutAttributes cause my 
CollectionViewDelegate and DataSources to fetch the cell I'm dragging around 
and change it (or does it not require the delegates or datasources ... ?)

Thanks,
-Luther



On Mon, Mar 7, 2016 at 2:45 PM, Luke Hiesterman 
<luket...@apple.com<mailto:luket...@apple.com>> wrote:
You can create your own subclass of UICollectionViewLayoutAttributes and add 
something like an “isMoving” property to that. Then teach your cell classes to 
respond to that property by changing the background color.

Luke

On Mar 7, 2016, at 11:44 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

Thanks Luke! That was it - I can drag and drop successfully now.

One more question, how do I modify a property of the item I'm dragging around 
if the property is NOT currently in UICollectionViewLayoutAttributes ... I 
don't see a call to the datasource or delegate when I select the cell for 
moving ... so I'm not sure how to change the background color to "red" for 
instance.

Would I have to add my own view to the superview and manually move it around in 
the dragging callbacks?

Thanks!
-Luther


On Mon, Mar 7, 2016 at 11:59 AM, Luke Hiesterman 
<luket...@apple.com<mailto:luket...@apple.com>> wrote:
I’d check your return value for this method in your layout:

- (UICollectionViewLayoutAttributes 
*)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath 
*)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);

Luke

On Mar 7, 2016, at 9:55 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

I followed the directions here,
http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
- to add iOS9 style dragging to my UICollectionView - and it sort of works.

As described in the article, I added a long press gesture recognizer and
wired it in to make calls on the collection view -- but now, if I long
press, the element under my finger disappears. As I drag the transparent
image around, the other elements shift - but I can never see the element I
am dragging around. When I let go, there is simply a hole left where I
"dropped" the element.

I do, very much, have a custom layout and I'm not sure that if, for drag, I
need to do anything special. Do I need to calculate the frame of the item I
am dragging around? I'm not sure what to try next except to roll my own
dragging. Any thoughts or things to try?

Thanks in advance.
__

Re: UICollectionView Moving

[Luther Baker]

> teach your cell classes to respond to that property

Want to think about this out loud. Wondering what would 'trigger' a lookup
on the layout's layoutAttributesForItemAtIndexPath ... and where would I
store the indexPath I am dragging around.

If I were to be more literal - in my view controller, I handle the
UIGestureRecognizerState.Began event. At this point, I can get the
indexPath of the element I am about to move and if I change something on
that cell at that time, it sticks for the life of the drag without
reference to layoutAttributes. I also handle the
UIGestureRecognizerState.Changed event and again, if I retrieve the cell at
the gesture's locationInView and change things in it ... those changes
stick until I let go of the drag.

Stepping into the custom layout for a minute ... as you suggested, I am now
implementing layoutAttributesForInteractivelyMovingItemAtIndexPath ... and
that is getting invoked in response to the
updateInteractiveMovementTargetPosition call I am making as the gesture
location changes. Now, I know the collection view's methods are triggering
the layout's callbacks - but I'm not sure what would trigger me to fetch
the custom attributes you are suggesting. At a minimum, to ask the layout
for the attributes at that indexPath, I'd have to actually be tracking the
'selectedIndexPath' in which case, I could just get the cell and modify it
directly.

I guess I'm wondering how to "teach my cells classes to respond to that
property" ... Cells are reused so I'm not even sure how I'd go about
setting up and tearing down a KVO type relationship for the specific cell I
am dragging around. Maybe there is a WWDC video that digs into this? or
it's an easy explain?

Sorry for being so long-winded. I'm not sure I'm communicating my question
well. Hope you can understand my underlying question and nudge me the right
way but at any rate, thanks for your help so far. I'd love to use an
elegant, "made for CollectionView" solution ... but I don't think I'm
looking at it correctly yet. Just in general I guess, how can a change to
the layoutAttributes cause my CollectionViewDelegate and DataSources to
fetch the cell I'm dragging around and change it (or does it not require
the delegates or datasources ... ?)

Thanks,
-Luther



On Mon, Mar 7, 2016 at 2:45 PM, Luke Hiesterman <luket...@apple.com> wrote:

> You can create your own subclass of UICollectionViewLayoutAttributes and
> add something like an “isMoving” property to that. Then teach your cell
> classes to respond to that property by changing the background color.
>
> Luke
>
> On Mar 7, 2016, at 11:44 AM, Luther Baker <lutherba...@gmail.com> wrote:
>
> Thanks Luke! That was it - I can drag and drop successfully now.
>
> One more question, how do I modify a property of the item I'm dragging
> around if the property is NOT currently in UICollectionViewLayoutAttributes
> ... I don't see a call to the datasource or delegate when I select the cell
> for moving ... so I'm not sure how to change the background color to "red"
> for instance.
>
> Would I have to add my own view to the superview and manually move it
> around in the dragging callbacks?
>
> Thanks!
> -Luther
>
>
> On Mon, Mar 7, 2016 at 11:59 AM, Luke Hiesterman <luket...@apple.com>
> wrote:
>
>> I’d check your return value for this method in your layout:
>>
>> - (UICollectionViewLayoutAttributes
>> *)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath
>> *)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);
>>
>> Luke
>>
>> On Mar 7, 2016, at 9:55 AM, Luther Baker <lutherba...@gmail.com> wrote:
>>
>> I followed the directions here,
>>
>> http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
>> - to add iOS9 style dragging to my UICollectionView - and it sort of
>> works.
>>
>> As described in the article, I added a long press gesture recognizer and
>> wired it in to make calls on the collection view -- but now, if I long
>> press, the element under my finger disappears. As I drag the transparent
>> image around, the other elements shift - but I can never see the element I
>> am dragging around. When I let go, there is simply a hole left where I
>> "dropped" the element.
>>
>> I do, very much, have a custom layout and I'm not sure that if, for drag,
>> I
>> need to do anything special. Do I need to calculate the frame of the item
>> I
>> am dragging around? I'm not sure what to try next except to roll my own
>> dragging. Any thoughts or things to try?
>>
>> Thanks in advance.
>> ___
>>
>> Cocoa-de

Re: UICollectionView Moving

[Luke Hiesterman]

You can create your own subclass of UICollectionViewLayoutAttributes and add 
something like an “isMoving” property to that. Then teach your cell classes to 
respond to that property by changing the background color.

Luke

On Mar 7, 2016, at 11:44 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

Thanks Luke! That was it - I can drag and drop successfully now.

One more question, how do I modify a property of the item I'm dragging around 
if the property is NOT currently in UICollectionViewLayoutAttributes ... I 
don't see a call to the datasource or delegate when I select the cell for 
moving ... so I'm not sure how to change the background color to "red" for 
instance.

Would I have to add my own view to the superview and manually move it around in 
the dragging callbacks?

Thanks!
-Luther


On Mon, Mar 7, 2016 at 11:59 AM, Luke Hiesterman 
<luket...@apple.com<mailto:luket...@apple.com>> wrote:
I’d check your return value for this method in your layout:

- (UICollectionViewLayoutAttributes 
*)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath 
*)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);

Luke

On Mar 7, 2016, at 9:55 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

I followed the directions here,
http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
- to add iOS9 style dragging to my UICollectionView - and it sort of works.

As described in the article, I added a long press gesture recognizer and
wired it in to make calls on the collection view -- but now, if I long
press, the element under my finger disappears. As I drag the transparent
image around, the other elements shift - but I can never see the element I
am dragging around. When I let go, there is simply a hole left where I
"dropped" the element.

I do, very much, have a custom layout and I'm not sure that if, for drag, I
need to do anything special. Do I need to calculate the frame of the item I
am dragging around? I'm not sure what to try next except to roll my own
dragging. Any thoughts or things to try?

Thanks in advance.
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Re: UICollectionView Moving

[Luther Baker]

Thanks Luke! That was it - I can drag and drop successfully now.

One more question, how do I modify a property of the item I'm dragging
around if the property is NOT currently in UICollectionViewLayoutAttributes
... I don't see a call to the datasource or delegate when I select the cell
for moving ... so I'm not sure how to change the background color to "red"
for instance.

Would I have to add my own view to the superview and manually move it
around in the dragging callbacks?

Thanks!
-Luther


On Mon, Mar 7, 2016 at 11:59 AM, Luke Hiesterman <luket...@apple.com> wrote:

> I’d check your return value for this method in your layout:
>
> - (UICollectionViewLayoutAttributes
> *)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath
> *)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);
>
> Luke
>
> On Mar 7, 2016, at 9:55 AM, Luther Baker <lutherba...@gmail.com> wrote:
>
> I followed the directions here,
>
> http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
> - to add iOS9 style dragging to my UICollectionView - and it sort of works.
>
> As described in the article, I added a long press gesture recognizer and
> wired it in to make calls on the collection view -- but now, if I long
> press, the element under my finger disappears. As I drag the transparent
> image around, the other elements shift - but I can never see the element I
> am dragging around. When I let go, there is simply a hole left where I
> "dropped" the element.
>
> I do, very much, have a custom layout and I'm not sure that if, for drag, I
> need to do anything special. Do I need to calculate the frame of the item I
> am dragging around? I'm not sure what to try next except to roll my own
> dragging. Any thoughts or things to try?
>
> Thanks in advance.
> ___
>
> Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
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Re: UICollectionView Moving

[Luke Hiesterman]

I’d check your return value for this method in your layout:

- (UICollectionViewLayoutAttributes 
*)layoutAttributesForInteractivelyMovingItemAtIndexPath:(NSIndexPath 
*)indexPath withTargetPosition:(CGPoint)position NS_AVAILABLE_IOS(9_0);

Luke

On Mar 7, 2016, at 9:55 AM, Luther Baker 
<lutherba...@gmail.com<mailto:lutherba...@gmail.com>> wrote:

I followed the directions here,
http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
- to add iOS9 style dragging to my UICollectionView - and it sort of works.

As described in the article, I added a long press gesture recognizer and
wired it in to make calls on the collection view -- but now, if I long
press, the element under my finger disappears. As I drag the transparent
image around, the other elements shift - but I can never see the element I
am dragging around. When I let go, there is simply a hole left where I
"dropped" the element.

I do, very much, have a custom layout and I'm not sure that if, for drag, I
need to do anything special. Do I need to calculate the frame of the item I
am dragging around? I'm not sure what to try next except to roll my own
dragging. Any thoughts or things to try?

Thanks in advance.
___

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UICollectionView Moving

[Luther Baker]

I followed the directions here,
http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/
- to add iOS9 style dragging to my UICollectionView - and it sort of works.

As described in the article, I added a long press gesture recognizer and
wired it in to make calls on the collection view -- but now, if I long
press, the element under my finger disappears. As I drag the transparent
image around, the other elements shift - but I can never see the element I
am dragging around. When I let go, there is simply a hole left where I
"dropped" the element.

I do, very much, have a custom layout and I'm not sure that if, for drag, I
need to do anything special. Do I need to calculate the frame of the item I
am dragging around? I'm not sure what to try next except to roll my own
dragging. Any thoughts or things to try?

Thanks in advance.
___

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Setting the contentOffset of a UICollectionView during update

[Colas B]

I have a collection view, with a custom layout, whose layout is changing when 
one taps on a cell: the cell becomes bigger. The layout is not a sublass of 
UIViewCollectionViewFlowLayout but directly of UICollectionViewLayout.
I update the layout with [self.collectionView performBatchUpdates:             
^{[self.tableView reloadItemsAtIndexPaths:indexPathsToUpdate];}                 
             completion:nil];  (I do implement the methods 
finalLayoutAttributesForDisappearingItemAtIndexPath: etc.)
The problem is that after the update, the contentOffset is not good anymore: I 
want the specific cell to be centered, but after the update it is not centered.

I tried to change the offset in the method finalizeCollectionViewUpdates: of my 
custom layout.I also tried to implement the method - 
targetContentOffsetForProposedContentOffset:
But the problem is always the same. During the animation, the cells that were 
not visible and become visible don't appear. They stay as "blank space" and 
only at the end of the animation they appear, all of a sudden.
So my question is, how to change the contentOffset of a UICollectionView during 
layout updates?
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Re: UICollectionView not obeying zIndex of UICollectionViewLayoutAttributes

[Ted Bradley]

Thanks for the reply. I made a standalone project in order to strip out all my 
extraneous code. In the process I think I found my own solution.

override func initialLayoutAttributesForAppearingItemAtIndexPath(itemIndexPath: 
NSIndexPath) - UICollectionViewLayoutAttributes?
override func 
finalLayoutAttributesForDisappearingItemAtIndexPath(itemIndexPath: NSIndexPath) 
- UICollectionViewLayoutAttributes?

were not also applying the new zIndex so I think this was what was causing it.

Just thought I should post back the solution in case this comes up in a search 
for anyone else.


Thanks again,

Ted

 On 6 Aug 2015, at 16:42, Luke Hiesterman luket...@apple.com wrote:
 
 Can you post your implementations -layoutAttributesForElementsInRect: as well 
 as -layoutAttributesForItemAtIndexPath:?
 
 Luke
 
 On Aug 6, 2015, at 8:09 AM, Ted Bradley earlte...@googlemail.com wrote:
 
 The effect I'm trying to achieve is a kind of sticky header cell. It's 
 important to me that the sticky cell floats over the top of the others. 
 Something a bit like this:
 
  ┌──┐ 
  │  │ 
  │  Cell 0  │ 
  │  ├┐
  └┬─┘│
   │  Cell 4  │
   │  │
   └──┘
   ┌──┐
   │  │
   │  Cell 5  │
   │  │
   └──┘
   ┌──┐
   │  │
   │  Cell 6  │
   │  │
   └──┘
 Cell 4, 5 and 6 would normally viewable and I'm constructing the attributes 
 for cell 0 in my UICollectionViewFlowLayout subclass during 
 layoutAttributesForElementsInRect:. All I do is call the super 
 implementation, determine which cell I need to add in and then construct the 
 UICollectionViewLayoutAttributes(forCellWithIndexPath:). I then set the 
 zIndex for it to 1 (default is `0`).
 
 The problem I'm getting is that the UICollectionView seems to always ignore 
 the `zIndex`
 
  ┌──┐ 
  │  │ 
  │  Cell 0  │ 
  │┌─┴┐
  └┤  │
   │  Cell 4  │
   │  │
   └──┘
   ┌──┐
   │  │
   │  Cell 5  │
   │  │
   └──┘
   ┌──┐
   │  │
   │  Cell 6  │
   │  │
   └──┘
 
 Now I believe it's possible to visually sort this out using a 3d transform, 
 but that doesn't work for me as I don't want any taps going to the cell 
 which is over the top. So in this example I don't want Cell 4 receiving taps 
 intended for Cell 0.
 
 Does anyone have any ideas? This is on iOS 8.4.
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UICollectionView not obeying zIndex of UICollectionViewLayoutAttributes

[Ted Bradley]

The effect I'm trying to achieve is a kind of sticky header cell. It's 
important to me that the sticky cell floats over the top of the others. 
Something a bit like this:

   ┌──┐ 
   │  │ 
   │  Cell 0  │ 
   │  ├┐
   └┬─┘│
│  Cell 4  │
│  │
└──┘
┌──┐
│  │
│  Cell 5  │
│  │
└──┘
┌──┐
│  │
│  Cell 6  │
│  │
└──┘
Cell 4, 5 and 6 would normally viewable and I'm constructing the attributes for 
cell 0 in my UICollectionViewFlowLayout subclass during 
layoutAttributesForElementsInRect:. All I do is call the super implementation, 
determine which cell I need to add in and then construct the 
UICollectionViewLayoutAttributes(forCellWithIndexPath:). I then set the zIndex 
for it to 1 (default is `0`).

The problem I'm getting is that the UICollectionView seems to always ignore the 
`zIndex`

   ┌──┐ 
   │  │ 
   │  Cell 0  │ 
   │┌─┴┐
   └┤  │
│  Cell 4  │
│  │
└──┘
┌──┐
│  │
│  Cell 5  │
│  │
└──┘
┌──┐
│  │
│  Cell 6  │
│  │
└──┘

Now I believe it's possible to visually sort this out using a 3d transform, but 
that doesn't work for me as I don't want any taps going to the cell which is 
over the top. So in this example I don't want Cell 4 receiving taps intended 
for Cell 0.

Does anyone have any ideas? This is on iOS 8.4.
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Re: UICollectionView not obeying zIndex of UICollectionViewLayoutAttributes

[Luke Hiesterman]

Can you post your implementations -layoutAttributesForElementsInRect: as well 
as -layoutAttributesForItemAtIndexPath:?

Luke

 On Aug 6, 2015, at 8:09 AM, Ted Bradley earlte...@googlemail.com wrote:
 
 The effect I'm trying to achieve is a kind of sticky header cell. It's 
 important to me that the sticky cell floats over the top of the others. 
 Something a bit like this:
 
   ┌──┐ 
   │  │ 
   │  Cell 0  │ 
   │  ├┐
   └┬─┘│
│  Cell 4  │
│  │
└──┘
┌──┐
│  │
│  Cell 5  │
│  │
└──┘
┌──┐
│  │
│  Cell 6  │
│  │
└──┘
 Cell 4, 5 and 6 would normally viewable and I'm constructing the attributes 
 for cell 0 in my UICollectionViewFlowLayout subclass during 
 layoutAttributesForElementsInRect:. All I do is call the super 
 implementation, determine which cell I need to add in and then construct the 
 UICollectionViewLayoutAttributes(forCellWithIndexPath:). I then set the 
 zIndex for it to 1 (default is `0`).
 
 The problem I'm getting is that the UICollectionView seems to always ignore 
 the `zIndex`
 
   ┌──┐ 
   │  │ 
   │  Cell 0  │ 
   │┌─┴┐
   └┤  │
│  Cell 4  │
│  │
└──┘
┌──┐
│  │
│  Cell 5  │
│  │
└──┘
┌──┐
│  │
│  Cell 6  │
│  │
└──┘
 
 Now I believe it's possible to visually sort this out using a 3d transform, 
 but that doesn't work for me as I don't want any taps going to the cell which 
 is over the top. So in this example I don't want Cell 4 receiving taps 
 intended for Cell 0.
 
 Does anyone have any ideas? This is on iOS 8.4.
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Serious bug for UICollectionView

[Colas B]

Dear cocoa-dev,

I am facing the following bug with `UICollectionView` in the **horizontal 
scrolling mode** (`iOS 8`, `iOS 7`, the only ones I have tested).

I would like to have your views on this bug and on how I could elegantly fix it 
(and possibly fix it so that when Apple fixes it, my fix won't bring unattended 
effects). The message is also for reporting the bug to the community. I have 
already sent a report to Apple.

I set up the collection view manually, and choose a flow layout with an 
horizontal scrolling.

UICollectionViewFlowLayout * layout = [[UICollectionViewFlowLayout alloc] 
init] ;
layout.scrollDirection = UICollectionViewScrollDirectionHorizontal ;
layout.minimumInteritemSpacing = 5 ;
layout.minimumLineSpacing = 100 ;

The bug happens when the cells in the UICollectionView does not have the same 
sizes.


-- when all the cells have the same size, 
  • minimumInteritemSpacing is for the vertical space between cells
  • minimumLineSpacing is for the horizontal space

-- BUT as soon as one of the cells have a different size, the roles are 
interchanged:
  • minimumInteritemSpacing is for the horizontal space between cells 
  • minimumLineSpacing is for the vertical space.

## Link to a minimal non-working example

https://github.com/colasjojo/TEST_COLLECTION_VIEW_BUG
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Set UICollectionView UIScrollViewDelegate delegate

[Mazzaroth M.]

Hi, I have a parent view controller that has two UICollectionViewController
subclasses as children in its view controller hierarchy. I'd like to set
the parentViewController as the Subclass1CollectionViewController and
Subclass2CollectionViewControllers' .colllectionView UIScrollView delegate.
However when I set the delegate, the compiler assumes I'm trying to assign
it as the UICollectionViewDelegate. UICollectionView is a subclass of
UIScrollView.. how do refer to its scrollview delegate pointer?

Xcode 6.0.1 iOS8.

self.bodyCollectionViewController.collectionView.backgroundColor =
UIColor.clearColor;

self.bodyCollectionViewController.collectionView.showsHorizontalScrollIndicator
= NO;

self.bodyCollectionViewController.collectionView.showsVerticalScrollIndicator
= NO;

self.bodyCollectionViewController.collectionView.delegate = self; //
warning -- Assigning to 'idUICollectionViewDelegate' from incompatible
type 'SCRPreviewViewController *const __strong'

@interface SCRPreviewViewController : UIViewController
UIScrollViewDelegate
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Re: Set UICollectionView UIScrollViewDelegate delegate

[Kyle Sluder]

On Oct 18, 2014, at 2:22 PM, Mazzaroth M. taomaili...@gmail.com wrote:
 
 Hi, I have a parent view controller that has two UICollectionViewController
 subclasses as children in its view controller hierarchy. I'd like to set
 the parentViewController as the Subclass1CollectionViewController and
 Subclass2CollectionViewControllers' .colllectionView UIScrollView delegate.
 However when I set the delegate, the compiler assumes I'm trying to assign
 it as the UICollectionViewDelegate. UICollectionView is a subclass of
 UIScrollView.. how do refer to its scrollview delegate pointer?

There is only one delegate property. UICollectionView redeclares the property 
it inherits from UIScrollView and retypes it as UICollectionViewDelegate, which 
extends UIScrollViewDelegate. Any object you assign as the collection view’s 
delegate *must* conform to UICollectionViewDelegate.

The good news is that every member of UICollectionViewDelegate is optional, so 
this is a trivial change.

--Kyle Sluder

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Re: UICollectionView parallax-like horizontal scrolling

[Luke Hiesterman]

There are multiple ways to skin this cat. One is to use two collection views 
and just modify the content offset of one of them in response to the scrolling 
of the other. 

The behavior can also be built into a layout if you want to use a single scroll 
view. You don’t need different types of cells - you just need your layout to 
make a choice about how it wants each index path to behave. As an example, I 
might create a two column layout where all the even numbered indexes are on the 
left and all the odd numbered indexes are on the right. Or maybe it would be 
something different than that - maybe the first section would go on the left 
and the second section would go on the right. Could be anything. Then if I 
decided I want the right column to scroll faster than normal to create the 
parallax effect, I would return YES from 
-shouldInvalidateLayoutForBoundsChange: and then modify the positions of the 
layout attributes for all the items in the right hand column based on some math 
relative to the content offset. This would accomplish updating the frames of 
the right hand column cells every frame that a scroll occurs and achieve the 
parallax effect.

Luke

 On Oct 15, 2014, at 10:01 PM, Mazzaroth M. taomaili...@gmail.com wrote:
 
 In the running apps view(double-tap Home button) there are two rows each
 which contain two different types of cells. How would one implement this
 using UICollectionView?
 
 I more or less want to do this where the lower row cells are slightly
 narrower than the upper row such that when you swipe to scroll, the items
 in both rows are centred on the screen at the same time but because the
 items in row 1 are slightly narrower, they will scroll slightly faster than
 the items in row 0 creating a parallax-like effect. An extreme example of
 this would be
 
 https://github.com/allaboutapps/A3ParallaxScrollView
 
 in the tree example, however this is done with a custom UIScrollView
 subclass.
 
 And so, I know that this is possible but not sure if I can do it with
 UICollectionView and may need to use UIScrollView instead(however would
 prefer to figure it out with UICollectionView).
 
 In my attempts for UICollectionView, I was thinking that I'd need to use
 one type of cell for row 0 and another type of cell for row 1, but it's not
 clear to me how to specify a different layout for each of the rows, which
 appears to be what I need to do.
 
 Any thoughts on this?
 
 maz
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Re: UICollectionView parallax-like horizontal scrolling

[Mazzaroth M.]

Thanks, will investigate your suggestions.

On Thu, Oct 16, 2014 at 10:54 AM, Luke Hiesterman luket...@apple.com
wrote:

 There are multiple ways to skin this cat. One is to use two collection
 views and just modify the content offset of one of them in response to the
 scrolling of the other.

 The behavior can also be built into a layout if you want to use a single
 scroll view. You don’t need different types of cells - you just need your
 layout to make a choice about how it wants each index path to behave. As an
 example, I might create a two column layout where all the even numbered
 indexes are on the left and all the odd numbered indexes are on the right.
 Or maybe it would be something different than that - maybe the first
 section would go on the left and the second section would go on the right.
 Could be anything. Then if I decided I want the right column to scroll
 faster than normal to create the parallax effect, I would return YES from
 -shouldInvalidateLayoutForBoundsChange: and then modify the positions of
 the layout attributes for all the items in the right hand column based on
 some math relative to the content offset. This would accomplish updating
 the frames of the right hand column cells every frame that a scroll occurs
 and achieve the parallax effect.

 Luke

  On Oct 15, 2014, at 10:01 PM, Mazzaroth M. taomaili...@gmail.com
 wrote:
 
  In the running apps view(double-tap Home button) there are two rows each
  which contain two different types of cells. How would one implement this
  using UICollectionView?
 
  I more or less want to do this where the lower row cells are slightly
  narrower than the upper row such that when you swipe to scroll, the items
  in both rows are centred on the screen at the same time but because the
  items in row 1 are slightly narrower, they will scroll slightly faster
 than
  the items in row 0 creating a parallax-like effect. An extreme example of
  this would be
 
  https://github.com/allaboutapps/A3ParallaxScrollView
 
  in the tree example, however this is done with a custom UIScrollView
  subclass.
 
  And so, I know that this is possible but not sure if I can do it with
  UICollectionView and may need to use UIScrollView instead(however would
  prefer to figure it out with UICollectionView).
 
  In my attempts for UICollectionView, I was thinking that I'd need to use
  one type of cell for row 0 and another type of cell for row 1, but it's
 not
  clear to me how to specify a different layout for each of the rows, which
  appears to be what I need to do.
 
  Any thoughts on this?
 
  maz
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UICollectionView parallax-like horizontal scrolling

[Mazzaroth M.]

In the running apps view(double-tap Home button) there are two rows each
which contain two different types of cells. How would one implement this
using UICollectionView?

I more or less want to do this where the lower row cells are slightly
narrower than the upper row such that when you swipe to scroll, the items
in both rows are centred on the screen at the same time but because the
items in row 1 are slightly narrower, they will scroll slightly faster than
the items in row 0 creating a parallax-like effect. An extreme example of
this would be

https://github.com/allaboutapps/A3ParallaxScrollView

in the tree example, however this is done with a custom UIScrollView
subclass.

And so, I know that this is possible but not sure if I can do it with
UICollectionView and may need to use UIScrollView instead(however would
prefer to figure it out with UICollectionView).

In my attempts for UICollectionView, I was thinking that I'd need to use
one type of cell for row 0 and another type of cell for row 1, but it's not
clear to me how to specify a different layout for each of the rows, which
appears to be what I need to do.

Any thoughts on this?

maz
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How to get variably sized header in a UICollectionView supporting both orientations

[David Hoerl]

Becoming increasingly adept at autolayout but currently stumped. What I 
am trying to do is design a UICollectionView header that using 
constraints is suitable for portrait and landscape.


I have a bunch of views in it, each grouped into a container view. What 
I'd like to do is when the view rotates, move the container views 
around. Currently this seems impossible because the size of the header 
(and footer) must be specified to the Flow Layout before the view is 
even created, and it appears to be fixed from them on.


As it stands now, what I'm doing is creating the header in code, and 
using knowledge of what orientation the view will be shown in, and 
varying the constraints on the container views. By reloading the 
collection view on every rotation, I can get a new (and properly) sized 
header.


This seems like driving a nail with a sledgehammer, but nothing else 
comes to mind. Very open to suggestions on better methods.


David
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Re: How to get variably sized header in a UICollectionView supporting both orientations

[David Duncan]

On Oct 4, 2013, at 11:35 AM, David Hoerl dho...@mac.com wrote:

 Becoming increasingly adept at autolayout but currently stumped. What I am 
 trying to do is design a UICollectionView header that using constraints is 
 suitable for portrait and landscape.
 
 I have a bunch of views in it, each grouped into a container view. What I'd 
 like to do is when the view rotates, move the container views around. 
 Currently this seems impossible because the size of the header (and footer) 
 must be specified to the Flow Layout before the view is even created, and it 
 appears to be fixed from them on.

Do you mean the header/footerReferenceSize properties? If so I would think this 
would just work, since the flow layout will automatically size the width or 
height (depending on the scrolling direction) to fill the width or height of 
the collection view, allowing your container to just specify its sizes relative 
to the parent view size without needing to know the orientation.

But maybe I just don’t understand exactly what you are running up against?

 
 As it stands now, what I'm doing is creating the header in code, and using 
 knowledge of what orientation the view will be shown in, and varying the 
 constraints on the container views. By reloading the collection view on every 
 rotation, I can get a new (and properly) sized header.
 
 This seems like driving a nail with a sledgehammer, but nothing else comes to 
 mind. Very open to suggestions on better methods.
 
 David
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--
David Duncan


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Re: How to get variably sized header in a UICollectionView supporting both orientations

[David Hoerl]

I have a bunch of views in it, each grouped into a container view. What I'd 
like to do is when the view rotates, move the container views around. Currently 
this seems impossible because the size of the header (and footer) must be 
specified to the Flow Layout before the view is even created, and it appears to 
be fixed from them on.


Do you mean the header/footerReferenceSize properties?


No

If so I would think this would just work, since the flow layout will 
automatically size the width or height (depending on the scrolling 
direction) to fill the width or height of the collection view, allowing 
your container to just specify its sizes relative to the parent view 
size without needing to know the orientation.


But maybe I just don’t understand exactly what you are running up against?


I have two sections, so have to use the Flow Delegate callback to supply 
the sizes:


  - (CGSize)collectionView:(UICollectionView *)collectionView 
layout:(UICollectionViewLayout*)collectionViewLayout 
referenceSizeForHeaderInSection:(NSInteger)section


The Flow Layout object asks for the sizes first, then the header (or 
footer if used). I tried returning one size in the above delegate 
method, then a larger header, but the collection view does not appear to 
look at the view's size, instead honoring the delegate returned value.


Hmmm - it looks like I overlooked sending the layout object 
invalidateLayout. I just did that in the willAnimate... rotation view 
controller method, and I observe the layout object asked again the the 
header height.


But its really odd - and I'm thinking about a bug report on this - that 
the delegate has to provide the size before the view is even created. So 
what I do now is create a header view in view did load, ask it for its 
size using systemLayoutSizeFittingSize, then release it, just to get the 
size (its using the new dynamic text so this is the only way to get its 
size). Later, Flow Layout asks for the size, then in another delegate 
call I dequeue a header view whose size I now know. I tried to cache the 
first view but that failed.



--
David Duncan






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Re: How to get variably sized header in a UICollectionView supporting both orientations

[Steve Christensen]

On Oct 4, 2013, at 1:52 PM, David Hoerl dho...@mac.com wrote:

 But its really odd - and I'm thinking about a bug report on this - that the 
 delegate has to provide the size before the view is even created.

It make sense if you think about it: it's asking for sizes so that scroll view 
contentSize can be set and the layout can be determined. It would be a lot more 
expensive to have to actually build each of the cells for the entire collection 
just to get their sizes. This sort of behavior also happens with UITableView 
and its various cells.


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Re: How to get variably sized header in a UICollectionView supporting both orientations

[David Hoerl]

On 10/4/13 5:09 PM, Steve Christensen wrote:

On Oct 4, 2013, at 1:52 PM, David Hoerl dho...@mac.com wrote:


But its really odd - and I'm thinking about a bug report on this - that the 
delegate has to provide the size before the view is even created.


It make sense if you think about it: it's asking for sizes so that scroll view 
contentSize can be set and the layout can be determined. It would be a lot more 
expensive to have to actually build each of the cells for the entire collection 
just to get their sizes. This sort of behavior also happens with UITableView 
and its various cells.



In the old days, you had static views. Now with dynamic type, and the 
ability to more easily support different dynamic portrait/landscape 
layouts (with autolayout), the views can change a lot. Also, for table 
headers and footers, you created the view then set or returned it.


With Collections you have to dequeue it, and ostensibly you can only 
do this when asked for a cell (since there is no way I know to dequeue a 
view then tell the collection that you don't really need it after all).


Maybe I could dequeue one early on, cache it to get the sizes, and the 
first time only I'm asked for the view, return the cached one (then nil 
out the reference). This seems like it might work but IMHO would be 
risky in terms of stretching the API.


I will probably at least try that out when I get everything else working.

David

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UICollectionView with NSFetchedResultsController; compatible?

[Michael Crawford]

I just finished watching Marcus Zarra's NSFetchedResultsController presentation 
from iDeveloper.tv .  At about 25 minutes into the presentation, Marcus says 
the NSFetchedResultsController only works well with table-view controllers.  I 
had planned to use it with a collection-view, which is why I reviewed the 
presentation in the first place.

What I'm looking for is more information on why it is not a good idea to mix 
these two classes.  What are the issues or pitfalls, in combining the two?

I did find think link to a project on GitHub where the author points out that:

 The trick is to queue the updates made through the 
 NSFetchedResultsControllerDelegate until the controller finishes its updates. 
 UICollectionView doesn't have the same beginUpdates and endUpdates that 
 UITableView has to let it work easily with NSFetchedResultsController, so you 
 have to queue them or you get internal consistency runtime exceptions.


Is this the only issue or are there other reasons to avoid combining these two 
types of controllers?

-Michael
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UICollectionView

[koko]

Given an array of UIImages as a data source I want to populate a UICollection 
with these images.

If I call -reloadData I see nothing in the view until the data source is 
exhausted then the view is displayed will all images.

How can the UICollectionView be told to display each cell / image as it is 
created? I want the user to see that something is happening.

-koko
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Re: UICollectionView

[David Duncan]

On May 8, 2013, at 11:06 AM, koko k...@highrolls.net wrote:

 Given an array of UIImages as a data source I want to populate a UICollection 
 with these images.
 
 If I call -reloadData I see nothing in the view until the data source is 
 exhausted then the view is displayed will all images.
 
 How can the UICollectionView be told to display each cell / image as it is 
 created? I want the user to see that something is happening.


Is the data source actually updating with new information? From the symptoms it 
sounds like that is not the case, and that it doesn't update until you've 
finished loading all of the images.
--
David Duncan


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