核心动画： 登录按钮的抖动效果：

CAKeyframeAnimation * kfAnimation = [CAKeyframeAnimation animationWithKeyPath:@"transform.translation.x"];        kfAnimation.values = @[@-10,@0,@10,@0];        kfAnimation.repeatCount = 2;        kfAnimation.duration = 0.2;        [loginButton.layer addAnimation:kfAnimation forKey:nil];