使用故事板在两个控制器之间传递数据 [英] Passing data between two controllers using storyboards

问题描述

我正在尝试将数据从一个 UITableViewController 传递给另一个。这是我在初始视图控制器中的代码：

I am trying to pass data from one UITableViewController to another. This is my code in the initial view controller:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
Subject *subject = (Subject *)[self.fetchedResultsController objectAtIndexPath:indexPath];
[self showList:subject animated:YES];
[self.tableView deselectRowAtIndexPath:indexPath animated:YES];
}

- (void)showList:(Subject *)subject animated:(BOOL)animated {
ListsViewController *lists = [[ListsViewController alloc] initWithStyle:UITableViewStyleGrouped];
lists.subject = subject;
NSLog(@"%@", lists.subject);

[self performSegueWithIdentifier:@"showDetail" sender:self];
}

日志输出显示它已经传递了我想要的数据。但是，当我执行segue并在中记录主题时，ListsViewController 显示为null。

The log output was showing that it had the data I wanted had been passed over. However when I perform the segue and log the subject in the ListsViewController is shows null.

任何想法？

推荐答案

您需要覆盖 prepareForSegue：sender： 方法。快速解决方案是

You need to overwrite prepareForSegue:sender: method. The quick fix would be

- (void)showList:(Subject *)subject animated:(BOOL)animated
{
     [self performSegueWithIdentifier:@"showDetail" sender:subject];
}

...

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"showDetail"]) {
        ListsViewController *controller = ([segue.destinationViewController isKindOfClass:[ListsViewController class]]) ? segue.destinationViewController : nil;
        controller.subject = ([sender isKindOfClass:[Subject class]]) ? subject : nil;
    }
}

你的代码不起作用的原因是你的 showList：animated：方法你创建了一个 ListsViewController 实例，并为它分配了一个主题，但这个视图控制器从未出现过。相反， performSegueWithIdentifier：sender 创建 ListsViewController 类的另一个实例，该类对主题<一无所知/ code>。这就是为什么你需要等待UIStoryboardSegue从故事板中实例化目标视图控制器，然后按照你想要的方式配置它，你可以在 prepareForSegue：sender：方法中进行配置。

The reason why your code did not work is that in your showList:animated: method you created a ListsViewController instance and assigned it a subject, but this view controller was never presented. Instead performSegueWithIdentifier:sender creates another instance of your ListsViewController class which knows nothing about your subject. That's why you need to wait for UIStoryboardSegue to instantiate a destination view controller from the storyboard and then configure it the way you want, which you can do in prepareForSegue:sender: method.

在 performSegueWithIdentifier中使用 subject 作为发件人可能不是最佳选择：sender 方法，因为它不是发送者:)。我要做的是在视图控制器类中创建一个属性主题并使用它 prepareForSegue：sender：

Also it might be not the best idea to use subject as a sender in performSegueWithIdentifier:sender method, because it's just not the sender :). What I would do is create a property subject in your view controller class and use it prepareForSegue:sender:

@interface MyViewController ()

@property (strong, nonatomic) Subject *subject;

@end


@implementation MyViewController

- (void)showList:(Subject *)subject animated:(BOOL)animated
{
    self.subject = subject;
    [self performSegueWithIdentifier:@"showDetail" sender:self];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"showDetail"]) {
        ListsViewController *controller = ([segue.destinationViewController isKindOfClass:[ListsViewController class]]) ? segue.destinationViewController : nil;
        controller.subject = self.subject;
    }
}

...
@end

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