ios通过按钮点击异步加载图片代码详解手机开发

@interface UIButton (AsyncImage) 
   
//size by point 
- (void)setImageFromURL:(NSString *)urlString adjustToSize:(CGSize)size completion:(void (^)(void))completion logo:(UIImage *)logoImage; 
   
@end 
   
   
@implementation UIButton (AsyncImage) 
   
- (void)setImageFromURL:(NSString *)urlString adjustToSize:(CGSize)size completion:(void (^)(void))completion logo:(UIImage *)logoImage 
{ 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
        UIImage *image = nil; 
        NSURL *url = [NSURL URLWithString:urlString]; 
        NSData *data = [NSData dataWithContentsOfURL:url]; 
        image = [UIImage imageWithData:data]; 
           
        if (image) { 
            if (!CGSizeEqualToSize(size, CGSizeZero)) { 
                image = [UIImage imageWithCGImage:image.CGImage scale:[self scaleImage:image adjustToSize:size] orientation:image.imageOrientation]; 
            } 
            if (logoImage) { 
                image = [self addLogoImage:logoImage toImage:image]; 
            } 
               
            dispatch_async(dispatch_get_main_queue(), ^{ 
                [self setImage:image forState:UIControlStateNormal]; 
                completion(); 
            }); 
        } 
        else { 
            NSLog(@"async load error."); 
        } 
    }); 
} 
   
// 缩放图片以适应按钮大小 
- (CGFloat)scaleImage:(UIImage *)image adjustToSize:(CGSize)size 
{ 
    CGFloat xScale = size.width / image.size.width; 
    CGFloat yScale = size.height / image.size.height; 
       
    return 1.0 / MIN(xScale, yScale); 
} 
   
- (UIImage *)addLogoImage:(UIImage *)logo toImage:(UIImage *)img 
{ 
    //get image width and height 
    CGFloat scale = [UIScreen mainScreen].scale; 
    int w = scale * img.size.width; 
    int h = scale * img.size.height; 
    int logoWidth = logo.scale * logo.size.width; 
    int logoHeight = logo.scale * logo.size.height; 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
       
    //create a graphic context with CGBitmapContextCreate 
    CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst); 
    CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage); 
    CGContextDrawImage(context, CGRectMake(w - logoWidth, 0, logoWidth, logoHeight), [logo CGImage]); 
    CGImageRef imageMasked = CGBitmapContextCreateImage(context); 
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace); 
       
    return [UIImage imageWithCGImage:imageMasked scale:scale orientation:img.imageOrientation]; 
} 
   
@end