iOS实现View镂空效果

需要通过一个mask图显示部分UI或者Icon资源。ios的控件自带alpha的值，但是这个值都是整个icon或者UI的透明效果，不能做到自定义的透明或者镂空效果。我们必须借助于mask资源图。

具体的方法：修改imageview的layer，即可完成这个工作。

CALayer *mask = [CALayer layer];
mask.contents = (id)[[UIImage imageNamed:@"mask.png"] CGImage];
mask.frame = CGRectMake(0, 0, <img_width>, <img_height>);
yourImageView.layer.mask = mask;
yourImageView.layer.masksToBounds = YES;

 //MARK:1. maskView（maskLayer）基本原理CGFloat width = 120.f;//底图self.baseImageView = [[UIImageView alloc]initWithFrame:CGRectMake(20, 20, width, width)];[_baseImageView setImage:[UIImage imageNamed:@"base"]];[self.view addSubview:_baseImageView];//mask 是有透明的self.maskImageView = [[UIImageView alloc]initWithFrame:CGRectMake(20, 20 + width + 20, width, width)];[_maskImageView setImage:[UIImage imageNamed:@"mask"]];[self.view addSubview:_maskImageView];//使用maskView的情况self.addImageView  = [[UIImageView alloc]initWithFrame:CGRectMake(20, 20 + (width + 20) * 2, width, width)];[_addImageView setImage:[UIImage imageNamed:@"base"]];UIImageView *mask  = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, width, width)];[mask setImage:[UIImage imageNamed:@"mask"]];[_addImageView setMaskView:mask];//iOS8.0之后才有 maskView不能用addSubView的方式来添加遮罩!!!/*iOS 8之前//    CALayer *layer = [CALayer layer];//    [layer setFrame:CGRectMake(0, 0, width, width)];//    [layer setContents:(id)[UIImage imageNamed:@"mask"].CGImage];//    [_addImageView.layer setMask:layer];*/[self.view addSubview:_addImageView];