iOS 为ImageView设置圆角

1.最简单的是直接设置imageVIew的layer的圆角属性（_img是一个imageVIew）

    _img.layer.cornerRadius=_img.frame.size.width/3;// 将图层的边框设置为圆角
    _img.layer.masksToBounds=YES;// 隐藏边界

2.为imageVIew的layer层设置圆角背景图片（可以把image view设置成任何想要的形状）

    CALayer* maskLayer = [CALayer layer];
    maskLayer.frame = CGRectMake(0, 0,_imgView3.frame.size.width,_imgView3.frame.size.height);
    maskLayer.contents = (id)[[UIImage imageNamed:@"headerBg"] CGImage];//为图层设置背景图片
    [_imgView3.layer setMask:maskLayer];

headerBg图片为

3.可以把图片剪切成圆角形状

-(id)createRoundedRectImage:(UIImage*)image size:(CGSize)size
{
    // the size of CGContextRef
    int w = size.width;
    int h = size.height;
    
    UIImage *img = image;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace,kCGImageAlphaPremultipliedFirst);
    CGRect rect = CGRectMake(0, 0, w, h);
    
    CGContextBeginPath(context);
    addRoundedRectToPath(context, rect, size.width/3, size.height/3);
    CGContextClosePath(context);
    CGContextClip(context);
    CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);
    CGImageRef imageMasked = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    return [UIImage imageWithCGImage:imageMasked];
}
static void addRoundedRectToPath(CGContextRef context, CGRect rect, float ovalWidth,
                                 float ovalHeight)
{
    float fw, fh;
    if (ovalWidth == 0 || ovalHeight == 0) {
        CGContextAddRect(context, rect);
        return;
    }
    
    CGContextSaveGState(context);
    CGContextTranslateCTM(context, CGRectGetMinX(rect), CGRectGetMinY(rect));
    CGContextScaleCTM(context, ovalWidth, ovalHeight);
    fw = CGRectGetWidth(rect) / ovalWidth;
    fh = CGRectGetHeight(rect) / ovalHeight;
    
    CGContextMoveToPoint(context, fw, fh/2);  // Start at lower right corner
    CGContextAddArcToPoint(context, fw, fh, fw/2, fh, 1);  // Top right corner
    CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 1); // Top left corner
    CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 1); // Lower left corner
    CGContextAddArcToPoint(context, fw, 0, fw, fh/2, 1); // Back to lower right
    
    CGContextClosePath(context);
    CGContextRestoreGState(context);
}

4.也可以用的透明圆角矩形覆盖合成图片来形成

- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
    
    CGImageRef maskRef = maskImage.CGImage;
    
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);
    
    CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);
    return [UIImage imageWithCGImage:masked];
}

如果是要圆角矩形形状的图片，1和3的效果相同。如果退形状要求高的话2，4的效果要好很多