iOS批量圖像下載完成和回調

Question

我有一個批量圖像網址，我想在所有圖像下載完成後調用一個自定義塊。

而我使用SDWebImage，下載圖像功能是異步的，所以我應該怎麼做？

Answer 1

您可以使用dispatch_group_t做到這一點：

dispatch_group_t group = dispatch_group_create(); 
for (NSURL *url in urls) { 
    dispatch_group_enter(group); 
    [[[SDWebImageManager sharedManager] imageDownloader] downloadImageWithURL:url options:SDWebImageDownloaderLowPriority progress:nil completed:^(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, BOOL finished) { 
     if (image) { 
      // download success 
     } 
     NSLog(@"download..."); 
     dispatch_group_leave(group); 
    }]; 
} 

dispatch_group_notify(group, dispatch_get_main_queue(), ^{ 
    NSLog(@"all download..."); 
});