Ios 我使用rs/SDWebImage进行异步图像加载。但函数仅在第一次调用时返回图像

我使用rs/SDWebImage进行异步图像加载。我正在解析json提要中的图像url，并将该url打包到我的函数中。但函数仅在第一次调用时返回图像。当我再次打电话时。。。它返回空。。。。我怎样才能解决这个问题

   ........
    for (id key1 in tempfileLevel) 
      {
        NSMutableDictionary *tempfileLevel1 = [[NSMutableDictionary alloc] init];
        tempfileLevel1 = [tempfileLevel valueForKey:key1];
        NSLog(@" tumbfile name  = %@ " , [tempfileLevel1 valueForKey:@"tumbfile"]);

        NSString *thumbpath = [[NSString alloc] init];
        thumbpath = [tempfileLevel1 valueForKey:@"tumbfile"];
        NSURL *turl = [NSURL URLWithString:thumbpath];

        UIImage *imageDetail;
        imageDetail = [self getimage:turl];
        NSMutableArray *thumbs;
        [thumbs addObject:imageDetail];

     }
   .......
   ......

    - (UIImage*)getImage:(NSURL*)myurl
     {

        SDWebImageManager *manager = [SDWebImageManager sharedManager];
        UIImage *cachedImage = [manager imageWithURL:myurl];
        if (cachedImage)
        {
            // Use the cached image immediatly
        }
        else
        {
            // Start an async download
            [manager downloadWithURL:myurl delegate:self];
        }
        NSLog(@" image we got = %@",cachedImage);
    return cachedImage;

    }

我要做什么来修复这个