UIImageView 显示不规则图片，类似微信聊天气泡图片展示效果

微信聊天气泡，图片充满显示，效果：

-(void)layoutSubviews

{

    [super layoutSubviews];

    CAShapeLayer * _maskLayer = [CAShapeLayer layer];

    

    _maskLayer.fillColor = [UIColor blackColor].CGColor;

    

    _maskLayer.strokeColor = [UIColor clearColor].CGColor;

    

    _maskLayer.frame = self.bounds;

    //(0.5,0.5,0.1,0.1)

    _maskLayer.contentsCenter =CGRectMake(0.5,0.6,0.1,0.1);

    

    _maskLayer.contentsScale = [UIScreen mainScreen].scale;

    

    //非常关键设置自动拉伸的效果且不变形

    if (self.model.isSender) { _maskLayer.contents = (id)[UIImage imageNamed:BUBBLE_RIGHT_IMAGE_NAME].CGImage;//气泡聊天图片 消息发送者 右侧气泡

    }else{

        _maskLayer.contents = (id)[UIImage imageNamed:BUBBLE_LEFT_IMAGE_NAME].CGImage;//气泡聊天图片 消息接受者者 左侧气泡

    }

    

    

    self.imageView.layer.mask = _maskLayer;

    self.imageView.layer.frame = self.bounds;

   

}