Question

I have this code:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    [picker dismissModalViewControllerAnimated:YES];

...

}

Unfortunately, it runs the rest of the code (which can take a few seconds) before dismissing the modal view controller. How can i make it dismiss it first, and then run the rest of the code?

Answer 1

It won’t dismiss the modal view controller or do any other UI updates until it gets back to the main run loop (i.e. the function returns).

If you have a task that is going to take a noticeable amount of time to complete, you should perform it on a background thread instead of on the main thread. The usual thing is to use performSelectorInBackground:withObject:; but do remember that any UI updates (e.g. when the operation is complete) must be done on the main thread, so your background method may have to use performSelectorOnMainThread:withObject:waitUntilDone:.

If you prefer blocks, you could use dispatch_async instead:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{
    // background operation
});

If you have a number of background operations, you could also look into NSOperationQueue for the background operation.