的cellForRowAtIndexPath始终无调用时从块内的tableView：的cellForRowAtIndexPath：

Question

我有从的tableView调用时的cellForRowAtIndexPath总是返回零一个问题：的cellForRowAtIndexPath：

事情是我实际调用的cellForRowAtIndexPath一个块内内的tableView ：cellForRowAtIndexPath：我想这可能是问题。

我使用加载（和缓存）ad hoc的远程图像填充单元格。当图像返回完全加载完成处理程序块（在tableView：cellForRowAtIndexPath :)内我需要再次获取该单元格，因为它可能已滚动出视图...所以我调用cellForRowAtIndexPath再次获取单元格 - cellForRowAtIndexPath将只返回一个单元如果它是可见的。在我的情况下，我从来没有得到它返回任何东西，但零。即使我滚动速度非常慢（或者速度很快，或者我试过的任何速度......）但我所得到的结果都是零。

我会尝试在这里得到一些代码，但在此之前有任何建议，为什么会发生这种情况 - 我想块的东西将是一个提示。

下面是代码：https://dl.dropboxusercontent.com/u/147970342/stackoverflow/appsappsappsappsapps.zip

的-tableView：的cellForRowAtIndexPath：实现：

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 
    NSNumber* numberAppleid = self.appids[indexPath.row]; 
    UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:@"Mycell" forIndexPath:indexPath]; 

    cell.textLabel.text = [NSString stringWithFormat:@"Appleid: %@", numberAppleid]; 

    NSString* appleidasstring = [NSString stringWithFormat:@"%@", numberAppleid]; 

    cell.imageView.hidden = YES; // Hide any previous until image loads 
    [self getAppIconForAppleid:appleidasstring handlerImage:^(UIImage *image) { 
     if (image == nil) { 
      return; 
     } 

     DLog(@"cellForRowAtIndexPath tableView: %@, indexPath: %@", tableView, indexPath); 
     UITableViewCell* localcell = [tableView cellForRowAtIndexPath:indexPath]; 
     if (localcell != nil) { 
      localcell.imageView.image = image; 
      localcell.imageView.hidden = NO; 
     } 
     else { 
      DLog(@"Nah indexpath is not visible for: %@ because localcell is nil.", appleidasstring); 
     } 
    }]; 


    return cell; 
} 

修正版本：

#define KEYAPPLEID @"keyappleid" 
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 
    NSNumber* numberAppleid = self.appids[indexPath.row]; 
    UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:@"Mycell" forIndexPath:indexPath]; 

    cell.textLabel.text = [NSString stringWithFormat:@"Appleid: %@", numberAppleid]; 

    NSString* appleidasstring = [NSString stringWithFormat:@"%@", numberAppleid]; 

    [cell setAssociativeObject:appleidasstring forKey:KEYAPPLEID]; 

    cell.imageView.hidden = YES; // Hide any previous until image loads 
    [self getAppIconForAppleid:appleidasstring handlerImage:^(UIImage *image) { 
     if (image == nil) { 
      return; 
     } 

     NSString* currentappleidofcell = [cell associativeObjectForKey:KEYAPPLEID]; 
     if ([currentappleidofcell isEqualToString:appleidasstring]) { 
      cell.imageView.image = image; 
      cell.imageView.hidden = NO; 
     } 
     else { 
      DLog(@"Returning appleid: %@ is not matching current appleid: %@", appleidasstring, currentappleidofcell); 
     } 
    }]; 


    return cell; 
} 

，并且需要这一类：https://stackoverflow.com/a/10319083/129202

Answer 1

如果该块位于tableView:cellForRowAtIndexPath:回调内，则可以直接在该块中引用单元格。该块将自动保持单元格，直到块消失。但是，请小心保留周期。如果块由单元所有，则必须使用对单元的弱引用。

所以您的实现应该是这样的：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    NSNumber* numberAppleid = self.appids[indexPath.row]; 

    // Create your own UITableViewCell subclass that has an "appleidasstring" property 
    MyTableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:@"Mycell" forIndexPath:indexPath]; 

    cell.textLabel.text = [NSString stringWithFormat:@"Appleid: %@", numberAppleid]; 

    NSString* appleidasstring = [NSString stringWithFormat:@"%@", numberAppleid]; 

    cell.imageView.hidden = YES; // Hide any previous until image loads 

    // Set the appleidasstring on the cell to be checked later 
    cell. getAppIconForAppleid:appleidasstring = appleidasstring; 

    // Modify the handler callback to also callback with the appleidasstring 
    [self 
     getAppIconForAppleid:appleidasstring 
     handlerImage:^(UIImage *image, NSString *imageAppleIdaString) 
     { 
      if (image == nil) { 
       return; 
      } 

      // Ensure the cell hasn't been repurposed for a 
      // different imageAppleIdaString 
      if ([cell.appleidasstring isEqualToString:imageAppleIdaString]) { 
       cell.imageView.image = image; 
       cell.imageView.hidden = NO; 
      } 
     } 
    ]; 

    return cell; 
}