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;

}