使用图层剪切

//图层处理
UIImage *image = [UIImage imageNamed:@"icon.png"];
UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(50, 100, 100,100)];
imageView.image = image;
imageView.layer.masksToBounds = YES;
imageView.layer.cornerRadius = imageView.frame.size.width/2;
[self.view addSubview:imageView];

通过Quartz2D将图形绘制出一张圆形图片

通常的解决的办法就是通过Quartz2D将图形绘制出一张圆形图片来进行显示。

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    UIImageView *imageView2 = [[UIImageView alloc] initWithFrame:CGRectMake(50, 250, 100, 100)];
    imageView2.image = [self imageWithSourceImage:image];
    [self.view addSubview:imageView2];
}

- (UIImage *)imageWithSourceImage:(UIImage *)sourceImage {
    UIGraphicsBeginImageContext(sourceImage.size);
    //bezierPathWithOvalInRect方法后面传的Rect,可以看作(x,y,width,height),前两个参数是裁剪的中心点,后面两个决定裁剪的区域是圆形还是椭圆.
    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height)];
    //把路径设置为裁剪区域(超出裁剪区域以外的内容会自动裁剪掉)
    [path addClip];
    //把图片绘制到上下文当中
    [sourceImage drawAtPoint:CGPointZero];
    //从上下文当中生成一张新的图片
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    //结束上下文
    UIGraphicsEndImageContext();
    //返回新的图片
    return newImage;
}