下载图片先获取图片尺寸

#pragma mark 获取图片大小

-(CGSize)downloadImageSizeWithURL:(id)imageURL

{

   NSURL* URL = nil;

   if([imageURL isKindOfClass:[NSURLclass]]){

        URL = imageURL;

    }

   if([imageURL isKindOfClass:[NSStringclass]]){

        URL = [NSURLURLWithString: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 = [[NSMutableURLRequestalloc] initWithURL:URL];

   NSString* pathExtendsion = [URL.pathExtensionlowercaseString];

    

    CGSize size = CGSizeZero;

   if([pathExtendsion isEqualToString:@"png"]){

        size =  [selfdownloadPNGImageSizeWithRequest:request];

    }

   else if([pathExtendsionisEqual:@"gif"])

    {

        size =  [selfdownloadGIFImageSizeWithRequest:request];

    }

   else{

        size = [selfdownloadJPGImageSizeWithRequest:request];

    }

    if(CGSizeEqualToSize(CGSizeZero, size))

    {

        NSData* data = [NSURLConnectionsendSynchronousRequest:[NSURLRequestrequestWithURL:URL] returningResponse:nilerror:nil];

       UIImage* image = [UIImageimageWithData: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 = [NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror:nil];

   if(data.length ==8)

    {

       int w1 = 0, w2 =0, w3 = 0, w4 =0;

        [datagetBytes:&w1 range:NSMakeRange(0,1)];

        [datagetBytes:&w2 range:NSMakeRange(1,1)];

        [datagetBytes:&w3 range:NSMakeRange(2,1)];

        [datagetBytes:&w4 range:NSMakeRange(3,1)];

       int w = (w1 << 24) + (w2 <<16) + (w3 << 8) + w4;

       int h1 = 0, h2 =0, h3 = 0, h4 =0;

        [datagetBytes:&h1 range:NSMakeRange(4,1)];

        [datagetBytes:&h2 range:NSMakeRange(5,1)];

        [datagetBytes:&h3 range:NSMakeRange(6,1)];

        [datagetBytes:&h4 range:NSMakeRange(7,1)];

       int h = (h1 << 24) + (h2 <<16) + (h3 << 8) + h4;

       return CGSizeMake(w, h);

    }

    returnCGSizeZero;

}

-(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=6-9"forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror:nil];

   if(data.length ==4)

    {

       short w1 = 0, w2 =0;

        [datagetBytes:&w1 range:NSMakeRange(0,1)];

        [datagetBytes:&w2 range:NSMakeRange(1,1)];

       short w = w1 + (w2 << 8);

       short h1 = 0, h2 =0;

        [datagetBytes:&h1 range:NSMakeRange(2,1)];

        [datagetBytes:&h2 range:NSMakeRange(3,1)];

       short h = h1 + (h2 << 8);

       return CGSizeMake(w, h);

    }

    returnCGSizeZero;

}

-(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=0-209"forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror: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;

        [datagetBytes:&w1 range:NSMakeRange(0x60,0x1)];

        [datagetBytes:&w2 range:NSMakeRange(0x61,0x1)];

       short w = (w1 << 8) + w2;

       short h1 = 0, h2 =0;

        [datagetBytes:&h1 range:NSMakeRange(0x5e,0x1)];

        [datagetBytes:&h2 range:NSMakeRange(0x5f,0x1)];

       short h = (h1 << 8) + h2;

       return CGSizeMake(w, h);

    }else {

       short word = 0x0;

        [datagetBytes:&word range:NSMakeRange(0x15,0x1)];

       if (word == 0xdb) {

            [datagetBytes:&word range:NSMakeRange(0x5a,0x1)];

           if (word == 0xdb) {//两个DQT字段

               short w1 = 0, w2 =0;

                [datagetBytes:&w1 range:NSMakeRange(0xa5,0x1)];

                [datagetBytes:&w2 range:NSMakeRange(0xa6,0x1)];

               short w = (w1 << 8) + w2;

               short h1 = 0, h2 =0;

                [datagetBytes:&h1 range:NSMakeRange(0xa3,0x1)];

                [datagetBytes:&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;

                [datagetBytes:&w1 range:NSMakeRange(0x60,0x1)];

                [datagetBytes:&w2 range:NSMakeRange(0x61,0x1)];

               short w = (w1 << 8) + w2;

               short h1 = 0, h2 =0;

                [datagetBytes:&h1 range:NSMakeRange(0x5e,0x1)];

                [datagetBytes:&h2 range:NSMakeRange(0x5f,0x1)];

               short h = (h1 << 8) + h2;

               return CGSizeMake(w, h);

            }

        }else {

           return CGSizeZero;

        }

    }

}