On Dec 6, 2010, at 9:21 PM, Laurent Daudelin wrote:
> On Dec 6, 2010, at 17:16, davel...@mac.com wrote:
>
>> On Dec 6, 2010, at 5:37 PM, Gustavo Pizano wrote:
>>
>>> Hello.
>>>
>>> My application is saving some data, and it takes a while to do it, it can
>>> be 1 second to 10 sec around.. Im doing some image processing, The thing
>>> is..
>>>
>>> I send the saving operation in another thread using the NSThread +
>>> detachNewThreadSelector:toTarget:withObject: method, and in the main
>>> thread I update a UIActivityIndicator, and stop it when I receive the
>>> NSThreadWillExitNotification. The problem is that when it takes long to
>>> save, it may seem the app is somehow stuck, even the spinning indicator is
>>> running. I wanted to change the ActivityIndicator to a progressview, but
>>> then I can't make it work because the saving process not on the main
>>> thread, i think.. correct me if Im wrong, Im not so much familiar with
>>> multithreaded apps.
>>>
>>> As for the saving process, what I do is the following.
>>>
>>> I have a Parent view which contains subviews, these subviews are drawing
>>> images. The user can modify this images, (scale and rotate), so when I save
>>> i encode these views so it will save the view's transform, and then I
>>> archive the data I encoded for all these subviews.
>>
>>
>> <your code deleted>
>>
>> You are correct that you cannot call GUI methods from other threads, but
>> NSObject (which all your UI objects inherit from) has the method.
>>
>> - (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg
>>
>> So from your other thread, you can update the progress indicator by using it
>> to call a method that updates the progress.
>>
>>
>> This is even easier if you are targeting iOS 4.0 and higher using Blocks and
>> GrandCentral Dispatch.
>>
>> Code typed in email (i.e., not tested):
>>
>> dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
>> 0), ^{
>> // code you want implemented on another thread goes here:
>>
>> dispatch_async(dispatch_get_main_queue(), ^{
>> // code executed on main thread goes here (i.e., updating the
>> progress indicator in your case
>>
>> });
>> });
>>
>> HTH,
>> Dave
>
> Maybe I'm missing something but aren't the UI actions supposed to happen in
> the main thread, in this case, he should really call
> "performSelectorOnMainThread:withObject:waitUntilDone:"?
>
> -Laurent.
I copied and pasted the wrong method. Yes, the onMainThread version is the one
to use for this.
The Grand Central Dispatch code is ok though as Conrad pointed out.
Dave
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