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
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