利用iOS动画来模拟音量振动条的实现

2.先创建一个音量振动条，并且设置好动画,动画是绕着底部缩放，设置锚点

 CALayer *bar = [CALayer layer];

 bar.backgroundColor = [UIColor redColor].CGColor;

 bar.bounds = CGRectMake(0, 0, 30, 100);

 bar.position = CGPointMake(15, 200);

 bar.anchorPoint = CGPointMake(0.5, 1);

 [layer addSublayer:bar];

 CABasicAnimation *anim = [CABasicAnimation animation];

 anim.keyPath = @"transform.scale.y";

 anim.toValue = @(0.1);

 anim.autoreverses = YES;

 anim.repeatCount = MAXFLOAT;

 [bar addAnimation:anim forKey:nil];

// 设置4个子层，3个复制层
 layer.instanceCount = 4;

 // 设置复制子层的相对位置，每个x轴相差40
 layer.instanceTransform = CATransform3DMakeTranslation(40, 0, 0);

 // 设置复制子层的延迟动画时长
 layer.instanceDelay = 0.3;