How to know if several blocks have completed execution before taking action?

Question

I'm using animateWithDuration:animations:completion: to move several elements of my User Interface (about 4 elements) before removeFromSuperview: is called.

My question is, how can I know that all those animations have completed before calling removeFromSuperview:?

Answer 1

Ok, to answer my own question.

I ended up doing something like this:

    // Create dispatch queue & group
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_t group = dispatch_group_create();

    // Two group enters
    dispatch_group_enter(group);
    dispatch_group_enter(group);

    // (notice the group parameter in dispatch_group_leave)
    [UIView animateWithDuration:0.3 animations:^{
        self.pickerView.frame = CGRectMake( self.pickerView.frame.origin.x
                                           , self.view.bounds.size.height + self.pickerView.frame.size.height/2
                                           , self.pickerView.frame.size.width
                                           , self.pickerView.frame.size.height);
    } completion:^(BOOL finished){
        dispatch_group_leave(group);
    }]; 


    [UIView animateWithDuration:0.3 animations:^{
        self.navigationBar.frame = CGRectMake( self.navigationBar.frame.origin.x
                                              , -self.navigationBar.frame.size.height
                                              , self.navigationBar.frame.size.width
                                              , self.navigationBar.frame.size.height);
    } completion:^(BOOL finished){
        dispatch_group_leave(group);
    }];

    // Finishing callback
    dispatch_group_notify(group, queue, ^{
        [self.view removeFromSuperview];
    });

    // Release the group
    dispatch_release(group);

I hope this can serve as an example for someone else.

Answer 2

You can also use CATransaction. It will catch any embedded animations:

 [CATransaction begin];
 [CATransaction setCompletionBlock:^{ // all animations finished here }];
 [UIView animateWithDuration...
 [UIView animateWithDuration...
 ...
 [CATransaction commit];

This would allow you to not have to keep track of the animations yourself.