viewWithTag在cellForRowAtIndexPath方法中返回nil

Question

我有一个带有自定义原型单元格的UITableViewController。在原型单元内部，我有2个标签和一个图像。这些标记为100，用于图像，101和102标记为标签。我试图访问此方法中的标签

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    if ([indexPath row] == 0) {
        static NSString *CellIdentifier = @"InfoCell";
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

        UIImageView *albumArtworkImageView = (UIImageView *)[cell viewWithTag:100];
        albumArtworkImageView.image = [self getAlbumArtworkWithSize:albumArtworkImageView.frame.size];

        UILabel *albumArtistLabel = (UILabel *)[cell viewWithTag:101];
        albumArtistLabel.text = [self getAlbumArtist];

        UILabel *albumInfoLabel = (UILabel *)[cell viewWithTag:102];
        albumInfoLabel.text = [self getAlbumInfo];

        return cell;
    } else {

        static NSString *CellIdentifier = @"Cell";
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];


        MPMediaQuery *audiobookQuery = [MPMediaQuery audiobooksQuery];
        MPMediaPropertyPredicate *albumPredicate = [MPMediaPropertyPredicate predicateWithValue: audiobookTitle forProperty: MPMediaItemPropertyAlbumTitle];
        [audiobookQuery addFilterPredicate:albumPredicate];
        NSArray *albumTracks = [audiobookQuery items];

        NSUInteger trackNumber = [[[albumTracks objectAtIndex:(indexPath.row-1)]  valueForProperty:MPMediaItemPropertyAlbumTrackNumber] unsignedIntegerValue];

        if (trackNumber) {
            cell.textLabel.text = [NSString stringWithFormat:@"%i. %@", trackNumber, [[[albumTracks objectAtIndex:(indexPath.row-1)] representativeItem] valueForProperty:MPMediaItemPropertyTitle]];
        } else {
            cell.textLabel.text = [[[albumTracks objectAtIndex:(indexPath.row-1)] representativeItem] valueForProperty:MPMediaItemPropertyTitle];
        }


        if ([self sameArtists]) {

            cell.detailTextLabel.text = @"";

        } else {

            if ([[[albumTracks objectAtIndex:(indexPath.row-1)] representativeItem] valueForProperty:MPMediaItemPropertyArtist]) {
                cell.detailTextLabel.text = [[[albumTracks objectAtIndex:(indexPath.row-1)] representativeItem] valueForProperty:MPMediaItemPropertyArtist];
            } else {
                cell.detailTextLabel.text = @"";
            }

        }

        return cell;
    }
}

继续看故事板

我遇到的问题是我从标签查看视图的行返回nil。我以前做过这种类型的查找，我无法弄清楚为什么他们返回nil。任何帮助将非常感激。我甚至不确定调试的好方法。我是一名C＃开发人员，试图学习objective-c / ios编程。谢谢！

Answer 1

我给你一个替代方案。为UITableViewCell创建一个自定义类并在那里声明它的视图;然后使用这些属性连接每个单元格的子视图并直接访问它们，而无需调用viewWithTag。

例如，在您的自定义单元格中：

@interface MyCustomCell : UITableViewCell

@property (strong, nonatomic) UIImageView *albumArtworkImageView;
@property (strong, nonatomic) UILabel *albumArtistLabel;
@property (strong, nonatomic) UILabel *albumInfoLabel;

并在您的cellForRowAtIndexPath方法中：

MyCustomCell *cell = (MyCustomCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
cell.albumArtworkImageView.image = [self getAlbumArtworkWithSize:albumArtworkImageView.frame.size];
cell.albumArtistLabel.text = [self getAlbumArtist];
cell.albumInfoLabel.text = [self getAlbumInfo];

请记住在故事板中的单元格中设置MyCustomCell。

希望这有帮助！