CABasicAnimation resets to initial value after animation completes

Question

Here's the answer, it's a combination of my answer and Krishnan's.

cabasicanimation.fillMode = kCAFillModeForwards;
cabasicanimation.removedOnCompletion = NO;

The default value is kCAFillModeRemoved. (Which is the reset behavior you're seeing.)

The problem with removedOnCompletion is the UI element does not allow user interaction.

I technique is to set the FROM value in the animation and the TO value on the object. The animation will auto fill the TO value before it starts, and when it's removed will leave the object at it's correct state.

// fade in
CABasicAnimation *alphaAnimation = [CABasicAnimation animationWithKeyPath: @"opacity"];
alphaAnimation.fillMode = kCAFillModeForwards;

alphaAnimation.fromValue = NUM_FLOAT(0);
self.view.layer.opacity = 1;

[self.view.layer addAnimation: alphaAnimation forKey: @"fade"];

Set the following property:

animationObject.removedOnCompletion = NO;

You can simply set the key of CABasicAnimation to position when you add it to the layer. By doing this, it will override implicit animation done on the position for the current pass in the run loop.

CGFloat yOffset = 30;
CGPoint endPosition = CGPointMake(someLayer.position.x,someLayer.position.y + yOffset);

someLayer.position = endPosition; // Implicit animation for position

CABasicAnimation * animation =[CABasicAnimation animationWithKeyPath:@"position.y"]; 

animation.fromValue = @(someLayer.position.y);
animation.toValue = @(someLayer.position.y + yOffset);

[someLayer addAnimation:animation forKey:@"position"]; // The explicit animation 'animation' override implicit animation

You can have more information on 2011 Apple WWDC Video Session 421 - Core Animation Essentials (middle of the video)