使用故事板在两个控制器之间传递数据

我正在尝试从一个传递数据UITableViewController到另一个。这是我在初始视图控制器中的代码：

- (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];
}

日志输出显示我想要的数据已被传递。但是，当我执行 segue 并记录时subject in the ListsViewController显示为空。

有任何想法吗？

你需要覆盖prepareForSegue:sender:方法。快速解决办法是

- (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;
    }
}

您的代码不起作用的原因是在您的showList:animated:您创建的方法ListsViewController实例并为其分配了一个subject，但这个视图控制器从未出现过。反而performSegueWithIdentifier:sender创建你的另一个实例ListsViewController类对你一无所知subject。这就是为什么您需要等待 UIStoryboardSegue 从故事板实例化目标视图控制器，然后按照您想要的方式配置它，您可以在prepareForSegue:sender: method.

另外，这可能不是使用的最佳主意subject作为发件人performSegueWithIdentifier:sender方法，因为它不是发件人:)。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:

@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