Objective-C – CABasicAnimation applying changes after animation?

by

When you add an animation to a layer, the animation does not change the layer’s properties. Instead, the system creates a copy of the layer. The original layer is called the model layer, and the duplicate is called the presentation layer. The presentation layer’s properties change as the animation progresses, but the model layer’s properties stay unchanged.

When you remove the animation, the system destroys the presentation layer, leaving only the model layer, and the model layer’s properties then control how the layer is drawn. So if the model layer’s properties don’t match the final animated values of the presentation layer’s properties, the layer will instantly reset to its appearance before the animation.

To fix this, you need to set the model layer’s properties to the final values of the animation, and then add the animation to the layer. You want to do it in this order because changing a layer property can add an implicit animation for the property, which would conflict with the animation you want to explicitly add. You want to make sure your explicit animation overrides the implicit animation.

So how do you do all this? The basic recipe looks like this:

CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"position"];
animation.fromValue = [NSValue valueWithCGPoint:myLayer.position];
layer.position = newPosition; // HERE I UPDATE THE MODEL LAYER'S PROPERTY
animation.toValue = [NSValue valueWithCGPoint:myLayer.position];
animation.duration = .5;
[myLayer addAnimation:animation forKey:animation.keyPath];

I haven’t used an animation group so I don’t know exactly what you might need to change. I just add each animation separately to the layer.

I also find it easier to use the +[CATransaction setCompletionBlock:] method to set a completion handler for one or several animations, instead of trying to use an animation’s delegate. You set the transaction’s completion block, then add the animations:

[CATransaction begin]; {
    [CATransaction setCompletionBlock:^{
        [self.imageView removeFromSuperview];
    }];
    [self addPositionAnimation];
    [self addScaleAnimation];
    [self addOpacityAnimation];
} [CATransaction commit];

More Related Contents:

  1. Does ARC work with Core Graphics objects?
  2. Chaining Core Animation animations
  3. How can I disable ARC for a single file in a project?
  4. @class vs. #import
  5. How do I use NSTimer?
  6. How to Check if an NSDate occurs between two other NSDates
  7. How does @synchronized lock/unlock in Objective-C?
  8. What exactly is a so called “Class Cluster” in Objective-C?
  9. Objective-C: Forward Class Declaration
  10. Regular expressions in an Objective-C Cocoa application
  11. How to Write OS X Finder plugin
  12. Best way to change the background color for an NSView
  13. Reading and writing images to an SQLite DB for iPhone use
  14. NavigationBar delay updating barTintColor iOS10
  15. Rotating a CGImage
  16. How to perform Callbacks in Objective-C
  17. iOS Background downloads when the app is not active
  18. ARC – The meaning of __unsafe_unretained?
  19. Dynamic forwarding: suppress Incomplete Implementation warning
  20. Monotonic clock on OSX
  21. How do I enable Local Storage in my WebKit-based application?
  22. #define vs const in Objective-C
  23. how to register the app to open the pdf file in my app in ipad
  24. Heart Rate data on apple Watch
  25. Is calling super in a category the same as calling it in a subclass?
  26. Xcode: Getting warning “implicit conversion from enumeration type UIDeviceOrientation”
  27. RestKit: How does one post an array of objects?
  28. When to use self on class properties?
  29. What’s the difference between declaring a variable “id” and “NSObject *”?
  30. viewDidLoad in NSViewController?

Leave a Comment