Forcing Consecutive Animations with CABasicAnimation

Question

I have a notification that fires in my model when certain properties change. As a result, a selector in a particular view object catches the notifications to change the position of the view accordingly.

The notifications causes a view on the window to move in a particular direction (always vertically or horizontally and always by a standard step size on the window). It's possible for the user-actions to cause several notifications to fire one after the other. For example, 3 notifications could be sent to move the view down three steps, then two more notifications could be sent to move the view to the right two steps.

The problem is that as I execute the animations, they don't happen consecutively. So, in the previous example, though I want the view to move slowly down three spaces and then move over two spaces as a result of the notifications, instead it ends up moving diagonally to the new position.

Here is the code for my two selectors (note that placePlayer sets the position of the view according to current information in the model):

- (void)moveEventHandler: (NSNotification *) notification
{
    [self placePlayer];

    CABasicAnimation* moveAnimation = [CABasicAnimation animationWithKeyPath:@"position"];
    moveAnimation.duration = 3;
    moveAnimation.fillMode = kCAFillModeForwards;  // probably not necessary
    moveAnimation.removedOnCompletion = NO;        // probably not necessary
    [[self layer] addAnimation:moveAnimation forKey:@"animatePosition"];
}

Any suggestions on how to make multiple calls to this methods force animation to execute step-by-step rather than all at once? Thanks!!

Answer 1

I think what you might want to do here is set up a queue of animations that need to happen consecutively and set the animations delegate so that you will receive the animationDidStop:finished: message. This way when one animation is completed you can set off the next one in the queue.