获取网络图片的大小

// 图片处理 0 半灰色  1 灰度   2 深棕色    3 反色  
+(UIImage*)imageWithImage:(UIImage*)image grayLevelType:(UIImageGrayLevelType)type;  
  
//色值 变暗多少 0.0 - 1.0  
+(UIImage*)imageWithImage:(UIImage*)image darkValue:(float)darkValue;  
  
/**  
    获取网络图片的Size, 先通过文件头来获取图片大小  
    如果失败 会下载完整的图片Data 来计算大小 所以最好别放在主线程 
    如果你有使用SDWebImage就会先看下 SDWebImage有缓存过改图片没有 
    支持文件头大小的格式 png、gif、jpg   http://www.cocoachina.com/bbs/read.php?tid=165823 
 */  
+(CGSize)downloadImageSizeWithURL:(id)imageURL; 

派生到我的代码片

    //讨厌警告  
    -(id)diskImageDataBySearchingAllPathsForKey:(id)key{return nil;}  
    +(CGSize)downloadImageSizeWithURL:(id)imageURL  
    {  
        NSURL* URL = nil;  
        if([imageURL isKindOfClass:[NSURL class]]){  
            URL = imageURL;  
        }  
        if([imageURL isKindOfClass:[NSString class]]){  
            URL = [NSURL URLWithString:imageURL];  
        }  
        if(URL == nil)  
            return CGSizeZero;  
          
        NSString* absoluteString = URL.absoluteString;  
          
    #ifdef dispatch_main_sync_safe  
        if([[SDImageCache sharedImageCache] diskImageExistsWithKey:absoluteString])  
        {  
            UIImage* image = [[SDImageCache sharedImageCache] imageFromMemoryCacheForKey:absoluteString];  
            if(!image)  
            {  
                NSData* data = [[SDImageCache sharedImageCache] performSelector:@selector(diskImageDataBySearchingAllPathsForKey:) withObject:URL.absoluteString];  
                image = [UIImage imageWithData:data];  
            }  
            if(image)  
            {  
                return image.size;  
            }  
        }  
    #endif  
          
        NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:URL];  
        NSString* pathExtendsion = [URL.pathExtension lowercaseString];  
          
        CGSize size = CGSizeZero;  
        if([pathExtendsion isEqualToString:@"png"]){  
            size =  [self downloadPNGImageSizeWithRequest:request];  
        }  
        else if([pathExtendsion isEqual:@"gif"])  
        {  
            size =  [self downloadGIFImageSizeWithRequest:request];  
        }  
        else{  
            size = [self downloadJPGImageSizeWithRequest:request];  
        }  
        if(CGSizeEqualToSize(CGSizeZero, size))  
        {  
            NSData* data = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:URL] returningResponse:nil error:nil];  
            UIImage* image = [UIImage imageWithData:data];  
            if(image)  
            {  
    #ifdef dispatch_main_sync_safe  
                [[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:YES imageData:data forKey:URL.absoluteString toDisk:YES];  
    #endif  
                size = image.size;  
            }  
        }  
        return size;  
    }  
    +(CGSize)downloadPNGImageSizeWithRequest:(NSMutableURLRequest*)request  
    {  
        [request setValue:@"bytes=16-23" forHTTPHeaderField:@"Range"];  
        NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];  
        if(data.length == 8)  
        {  
            int w1 = 0, w2 = 0, w3 = 0, w4 = 0;  
            [data getBytes:&w1 range:NSMakeRange(0, 1)];  
            [data getBytes:&w2 range:NSMakeRange(1, 1)];  
            [data getBytes:&w3 range:NSMakeRange(2, 1)];  
            [data getBytes:&w4 range:NSMakeRange(3, 1)];  
            int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;  
            int h1 = 0, h2 = 0, h3 = 0, h4 = 0;  
            [data getBytes:&h1 range:NSMakeRange(4, 1)];  
            [data getBytes:&h2 range:NSMakeRange(5, 1)];  
            [data getBytes:&h3 range:NSMakeRange(6, 1)];  
            [data getBytes:&h4 range:NSMakeRange(7, 1)];  
            int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;  
            return CGSizeMake(w, h);  
        }  
        return CGSizeZero;  
    }  
    +(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request  
    {  
        [request setValue:@"bytes=6-9" forHTTPHeaderField:@"Range"];  
        NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];  
        if(data.length == 4)  
        {  
            short w1 = 0, w2 = 0;  
            [data getBytes:&w1 range:NSMakeRange(0, 1)];  
            [data getBytes:&w2 range:NSMakeRange(1, 1)];  
            short w = w1 + (w2 << 8);  
            short h1 = 0, h2 = 0;  
            [data getBytes:&h1 range:NSMakeRange(2, 1)];  
            [data getBytes:&h2 range:NSMakeRange(3, 1)];  
            short h = h1 + (h2 << 8);  
            return CGSizeMake(w, h);  
        }  
        return CGSizeZero;  
    }  
    +(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request  
    {  
        [request setValue:@"bytes=0-209" forHTTPHeaderField:@"Range"];  
        NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];  
          
        if ([data length] <= 0x58) {  
            return CGSizeZero;  
        }  
          
        if ([data length] < 210) {// 肯定只有一个DQT字段  
            short w1 = 0, w2 = 0;  
            [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];  
            [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];  
            short w = (w1 << 8) + w2;  
            short h1 = 0, h2 = 0;  
            [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];  
            [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];  
            short h = (h1 << 8) + h2;  
            return CGSizeMake(w, h);  
        } else {  
            short word = 0x0;  
            [data getBytes:&word range:NSMakeRange(0x15, 0x1)];  
            if (word == 0xdb) {  
                [data getBytes:&word range:NSMakeRange(0x5a, 0x1)];  
                if (word == 0xdb) {// 两个DQT字段  
                    short w1 = 0, w2 = 0;  
                    [data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];  
                    [data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];  
                    short w = (w1 << 8) + w2;  
                    short h1 = 0, h2 = 0;  
                    [data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];  
                    [data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];  
                    short h = (h1 << 8) + h2;  
                    return CGSizeMake(w, h);  
                } else {// 一个DQT字段  
                    short w1 = 0, w2 = 0;  
                    [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];  
                    [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];  
                    short w = (w1 << 8) + w2;  
                    short h1 = 0, h2 = 0;  
                    [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];  
                    [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];  
                    short h = (h1 << 8) + h2;  
                    return CGSizeMake(w, h);  
                }  
            } else {  
                return CGSizeZero;  
            }  
        }  
    }