ios - UITableViewCell imageView 没有得到更新

Question

为什么图像不会显示在单元格上？我想这与线程有关。

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
   static NSString *CellIdentifier = @"Cell";
   UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
   if (!cell) {
      cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
      cell.selectionStyle = UITableViewCellSelectionStyleNone;
   }
   GKTurnBasedMatch *match = [matches objectAtIndex:indexPath.row];
   GKTurnBasedParticipant *part = [match.participants objectAtIndex:0];

   [GKPlayer loadPlayersForIdentifiers:@[part.playerID] withCompletionHandler:^(NSArray *players, NSError *error) {
      if(error == nil && players.count == 1) {
         GKPlayer *player = [players lastObject];
         [player loadPhotoForSize:GKPhotoSizeSmall withCompletionHandler:^(UIImage *photo, NSError *error) {
            dispatch_async(dispatch_get_main_queue(), ^{
               cell.imageView.image = [UIImage imageNamed:@"coins.png"]; //Doesnt work
            });
         }];
      }
   }];
   //cell.imageView.image = [UIImage imageNamed:@"coins.png"]; //This Works
   [cell.textLabel setText:part.playerID];
   return cell;
}

下面的代码有效，谢谢

dispatch_async(dispatch_get_main_queue(), ^{
               UITableViewCell *cellToUpdate = [self.tableView cellForRowAtIndexPath:indexPath];
               if (cellToUpdate != nil && photo != nil) {
                  cellToUpdate.imageView.image = photo;
                  [cellToUpdate setNeedsLayout];

               }
            });