AFNetworking 异步下载 GIF 带占位符

Posted 2023-02-24

【中文标题】AFNetworking 异步下载 GIF 带占位符

【英文标题】：AFNetworking async download GIF with placeholder

【发布时间】：2013-10-26 16:15:34

【问题描述】：

我一直在使用 AFNetworking 与占位符异步下载 UIImage，它适用于 JPEG 和 PNG，但是我使用 library 来处理我的 GIF 图片。当我同步进行时效果很好。但是，我想使用 AFNetworking 异步下载图像，同时在 ImageView 中显示占位符图像。我怎样才能做到这一点？谢谢！

这是我的代码：

- (void) downloadAllImagesForComment

    if (_imageLinkList.count > 0)
    
        if (images == nil)
            images = [[NSMutableDictionary alloc] init];

        for (NSDictionary *URL in _imageLinkList) 
            if ([images objectForKey:[URL objectForKey:@"link"]] == nil)
            
                /*
                 * imageType = 0 <= other
                 * imageType = 1 <= gif
                 */
                int imageType = 0;

                NSURL *url = [NSURL URLWithString:[URL objectForKey:@"link"]];
                NSError *error = [[NSError alloc] init];
                NSLog(@"Retrieving imageData...");
                NSData *imageData = [NSData dataWithContentsOfURL:url options:NSDataReadingMappedIfSafe error:&error];
                NSLog(@"Retrived imageData.");
                uint8_t c;
                [imageData getBytes:&c length:1];

                switch (c) 
                    case 0xFF:
                        NSLog(@"image/jpeg");
                        imageType = 0;
                        break;
                    case 0x89:
                        NSLog(@"image/png");
                        imageType = 0;
                        break;
                    case 0x47:
                        NSLog(@"image/gif");
                        imageType = 1;
                        break;
                    case 0x49:
                        imageType = 0;
                        break;
                    case 0x4D:
                        NSLog(@"image/tiff");
                        imageType = 0;
                        break;
                

                UIImageView *temp_imageView;
                if (imageType == 1)
                
                // GIF IMAGE SHOULD BE INITIALIZED HERE!!!!!!
//                    image = [UIImage animatedImageWithAnimatedGIFData:imageData];
                
                else
                

                    temp_imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 280, 250)];
                    [temp_imageView setImageWithURL:url placeholderImage:[UIImage imageNamed:@"patch_la"]];
                

                [images setValue:temp_imageView forKey:[URL objectForKey:@"link"]];

                NSLog(@"Done downloading image: %@", [URL objectForKey:@"link"]);

            
        
    

【参考方案1】：

我建议使用SDWebImage library。它内置了异步动画 Gif 支持。

包含库后，就很简单了（只需将 NSURL 指向远程 Gif）：

[imageView setImageWithURL:[NSURL] completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType)];