Re: Calculations in a tableview
Thanks to all who helped me on and off the list. After a good night sleep and a day off coding, I think I finally got it :-) On 28/07/2011, at 23:15 , Quincey Morris wrote: So how does the array controller enter this picture at all? It's a glue object (aka mediating controller) whose function is to sort and filter the model array property. It has no role in sourcing actual data to your table. This was the key! Thanks again, Andre Masse ___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Calculations in a tableview
Hi, For example, lets say I have a tableview with 3 columns: quantity, unit price and total. I want to calculate total using (quantity * unit price). Pretty simple using a datasource but I've no idea how to do that with bindings (using an NSArrayController). Any pointer to an example of this would be greatly appreciated. Thanks, Andre Masse ___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Calculations in a tableview
On 28 Jul 2011, at 23:48, Andre Masse wrote: Hi, For example, lets say I have a tableview with 3 columns: quantity, unit price and total. I want to calculate total using (quantity * unit price). Pretty simple using a datasource but I've no idea how to do that with bindings (using an NSArrayController). Any pointer to an example of this would be greatly appreciated. To be honest, this, along with the many debugging issues of bindings is exactly why I still use data sources. Bob___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Calculations in a tableview
Well, I may end up doing this… Thanks Andre Masse On 28/07/2011, at 18:52 , Thomas Davie wrote: On 28 Jul 2011, at 23:48, Andre Masse wrote: Hi, For example, lets say I have a tableview with 3 columns: quantity, unit price and total. I want to calculate total using (quantity * unit price). Pretty simple using a datasource but I've no idea how to do that with bindings (using an NSArrayController). Any pointer to an example of this would be greatly appreciated. To be honest, this, along with the many debugging issues of bindings is exactly why I still use data sources. Bob ___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Calculations in a tableview
Try value transformers Thanks Rajendran P On 7/29/11 6:18 AM, Andre Masse andre.ma...@videotron.ca wrote: Well, I may end up doing this... Thanks Andre Masse On 28/07/2011, at 18:52 , Thomas Davie wrote: On 28 Jul 2011, at 23:48, Andre Masse wrote: Hi, For example, lets say I have a tableview with 3 columns: quantity, unit price and total. I want to calculate total using (quantity * unit price). Pretty simple using a datasource but I've no idea how to do that with bindings (using an NSArrayController). Any pointer to an example of this would be greatly appreciated. To be honest, this, along with the many debugging issues of bindings is exactly why I still use data sources. Bob ___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/rpichaim%40juniper.net This email sent to rpich...@juniper.net ___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Calculations in a tableview
On Jul 28, 2011, at 15:48, Andre Masse wrote:
For example, lets say I have a tableview with 3 columns: quantity, unit price
and total. I want to calculate total using (quantity * unit price). Pretty
simple using a datasource but I've no idea how to do that with bindings
(using an NSArrayController).
Well, that's the problem right there. You seem to think bindings have something
to do with array controllers. They don't. (Bindings and array controllers are
often used together, of course, both on the content side of the array
controller and on the arrangedObjects side, but that's just a case of two
things being used to complement each other.)
When working with bindings, it helps to be very diligent in thinking in terms
of properties.
If you're supplying a table view's cells via bindings, then you must have a
model property for *each* column. In your case, your data model is (or
includes) an array property (say, invoiceItems), whose elements are objects
(of class, say, InvoiceItem) with properties quantity, unitPrice and
totalPrice.
If the total is always calculated from the other two properties, it is
typically a derived property (one whose value is derived on the fly, rather
than actually stored), but aside from that implementation detail, there's no
difference in how you use the properties to populate your table.
In code terms, the short answer to your question is:
+ (NSSet) keyPathsForValuesAffectingTotalPrice {
return [NSSet setWithObjects: @quantity, @unitPrice, nil];
}
- (NSInteger) totalPrice { // or whatever the correct data type is
return self.quantity * self.unitPrice;
}
The second method provides the derived property value. The first method
provides KVO compliance.
So how does the array controller enter this picture at all? It's a glue object
(aka mediating controller) whose function is to sort and filter the model
array property. It has no role in sourcing actual data to your table***.
*** It's certainly possible to *give* it a role, but I would argue that this is
a terrible idea.
___
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Re: Calculations in a tableview
Hi, On 29 Jul 11, at 10:51am, cocoa-dev-requ...@lists.apple.com wrote: For example, lets say I have a tableview with 3 columns: quantity, unit price and total. I want to calculate total using (quantity * unit price). Pretty simple using a datasource but I've no idea how to do that with bindings (using an NSArrayController). Any pointer to an example of this would be greatly appreciated. (Using Core Data with tables) I just write a method to calculate quantity * price and then bind the third column to that. Cheers, Steve___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Calculations in a tableview
Thanks a lot for the clarifications about the role of the NSArrayController. I
somehow got confused about the whole binding thing, its not so muddy now. Now,
the example I gave was a bad simplification of the real thing as the
totalPrice is more a proposedTotalPrice. It's based on a calculation but
can/will be changed by the user.
So, what I need is a way to calculate a property, but let the user change it if
he wants. For example, having 3 values a, b and c (a + b = c). The user
enters a value for a or b, then c is calculated. If the user changes c,
it now lose its dependance on a and b. This would be easy if the 3 values
were in an NSTextField instead of a tableview as I could add an action to the
first 2 fields and none to the third.
Is this can be done using bindings or should I stop fighting the framework and
and use a datasource?
Thanks,
Andre Masse
On 28/07/2011, at 22:13 , Quincey Morris wrote:
On Jul 28, 2011, at 15:48, Andre Masse wrote:
For example, lets say I have a tableview with 3 columns: quantity, unit
price and total. I want to calculate total using (quantity * unit price).
Pretty simple using a datasource but I've no idea how to do that with
bindings (using an NSArrayController).
Well, that's the problem right there. You seem to think bindings have
something to do with array controllers. They don't. (Bindings and array
controllers are often used together, of course, both on the content side of
the array controller and on the arrangedObjects side, but that's just a
case of two things being used to complement each other.)
When working with bindings, it helps to be very diligent in thinking in terms
of properties.
If you're supplying a table view's cells via bindings, then you must have a
model property for *each* column. In your case, your data model is (or
includes) an array property (say, invoiceItems), whose elements are objects
(of class, say, InvoiceItem) with properties quantity, unitPrice and
totalPrice.
If the total is always calculated from the other two properties, it is
typically a derived property (one whose value is derived on the fly, rather
than actually stored), but aside from that implementation detail, there's no
difference in how you use the properties to populate your table.
In code terms, the short answer to your question is:
+ (NSSet) keyPathsForValuesAffectingTotalPrice {
return [NSSet setWithObjects: @quantity, @unitPrice, nil];
}
- (NSInteger) totalPrice { // or whatever the correct data type is
return self.quantity * self.unitPrice;
}
The second method provides the derived property value. The first method
provides KVO compliance.
So how does the array controller enter this picture at all? It's a glue
object (aka mediating controller) whose function is to sort and filter the
model array property. It has no role in sourcing actual data to your table***.
*** It's certainly possible to *give* it a role, but I would argue that this
is a terrible idea.
___
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Re: Calculations in a tableview
On Jul 28, 2011, at 20:00, Andre Masse wrote: Is this can be done using bindings or should I stop fighting the framework and and use a datasource? It can be done with bindings***. All you've done is clarified that totalPrice isn't a derived property after all. So, you make a regular property (with getter and setter), and initialize the instance variable that backs it to the default value (items * price). Or, you can initialize the instance variable to a not set value (like 0 or NSNotFound, or something), but then you won't be able to just @synthesize the property -- you'll have to write code to return either the default or the explicit value, depending on the contents of the instance variable. (Or, you can have a BOOL instance variable that says whether the default has been overridden, but in that case you'll have to add code to the setter instead.) And, incidentally, what you are trying to do is in no way fighting the framework. You're doing exactly what you're supposed to be doing. :) *** Again, focus your thinking on *properties*. Ask yourself what properties your data model needs to support the user interaction, and it should become immediately clear what to do. Bindings are a way of hooking up (in this case) your UI to your data model's properties. They don't replace the data model design part of the process. ___ 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 Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
