呼吸效果

比如想实现一个图片的放大缩小的呼吸效果
放大的动画时长是 2s、缩小的动画时长是 1s

output.gif

代码处理

采用 CAAnimationGroup 方式实现，但是需要注意起始时间 beginTime 的参数设置

代码块
        // 创建动画组
        CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
        animationGroup.duration = 3; /// 子动画的总时长
        animationGroup.repeatCount = MAXFLOAT; /// 循环次数
        animationGroup.removedOnCompletion = YES;
        animationGroup.fillMode = kCAFillModeForwards;
//      animationGroup.autoreverses = YES;   自动反向执行动画，不能打开否则会异常

        // 放大
        CABasicAnimation *scaleUpAnimation = [CABasicAnimation animation];
        scaleUpAnimation.keyPath = @"transform.scale";
        scaleUpAnimation.duration = 2;
        scaleUpAnimation.fromValue = @1.0;
        scaleUpAnimation.toValue = @3;

        // 缩小
        CABasicAnimation *scaleDownAnimation = [CABasicAnimation animation];
        scaleDownAnimation.keyPath = @"transform.scale";
        scaleDownAnimation.beginTime = 2;  ///  从第 2s 开始执行缩小
        scaleDownAnimation.duration = 1;
        scaleDownAnimation.fromValue = @3;
        scaleDownAnimation.toValue = @1.0;
        animationGroup.animations = @[scaleUpAnimation,scaleDownAnimation];
  
        // 图片
        [self.imageView.layer addAnimation:animationGroup forKey:@"groups"];