为什么我的自定义委托不工作？

Question

我正在尝试构建一个委托，以允许我将数据从子视图控制器传递给父视图控制器。我一直在网上查看各种教程/问题，但我的委托方法没有被触发。

你能看一下我下面的代码，看看我是否遗漏了什么吗？

TownListViewController.h

@protocol TownListViewControllerDelegate;

@interface TownListViewController : UITableViewController <NSFetchedResultsControllerDelegate> {

    id <TownListViewControllerDelegate> delegate;

}

@property (nonatomic, assign) id <TownListViewControllerDelegate> delegate;

@end

@protocol TownListViewControllerDelegate
@optional

- (void)didSelectTown:(Town *)town;

@end

TownListViewController.m

@implementation TownListViewController

@synthesize delegate;

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    [delegate didSelectTown:(Town *)[self.fetchedResultsController objectAtIndexPath:indexPath]];
    [self.navigationController popViewControllerAnimated:YES];
}

@end

SearchViewController.h

@interface SearchViewController : UITableViewController <TownListViewControllerDelegate> {

...

}

SearchViewController.m

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    TownListViewController * townViewController = [[TownListViewController alloc] initWithNibName:@"TownListViewController" bundle:nil];
    townViewController.delegate = self;
    [self.navigationController pushViewController:townViewController animated:YES];
}

- (void)didSelectTown:(Town *)town
{
    NSLog(@"didSelectTown fired");
    self.selectedTown = town;
}

非常感谢任何帮助。

Answer 1

设置委托后尝试重新加载数据。我认为对表的 reloadData 的第一次调用发生在 TownListViewController 的 initWithNibName 期间...无论如何，您可以在此方法上发布 delegate 值吗：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath

我打赌是 nil...

顺便说一下，这是一个很好的方法练习检查变量 delegate 是否符合协议，尝试在假设该方法是可选的情况下添加此行：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    if([delegate conformsToProtocol(TownListViewControllerDelegate)] && [delegate respondsToSelector:@selector(didSelectTown:objectAtIndexPath:)])
        [delegate didSelectTown:(Town *)[self.fetchedResultsController objectAtIndexPath:indexPath]];
    [self.navigationController popViewControllerAnimated:YES];
}