Objective c segue数据传递返回nil

我需要将NSString传递给另一个ViewController，但它始终返回nil

//prepareForSegue is called from didSelectRowAtIndexPath
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if([[segue identifier] isEqualToString:@"chat"]) {
        NSString *userName = (NSString *) [toUsersArray objectAtIndex:[self.chatsTableView indexPathForSelectedRow].row];

        UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];

    ChatViewController *chatViewController = [storyboard instantiateViewControllerWithIdentifier:@"ChatViewController"];
    //[chatViewController setChatWithUser:userName]; EVEN TRIED:
    chatViewController.chatWithUser = username;
    }

}

下面是我声明NSString的地方：

@interface ChatViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, MessageDelegate> {
UITextField     *messageField;
NSString        *chatWithUser;
UITableView     *chatTableView;
NSMutableArray  *messagesArray;
}

@property (nonatomic,retain) IBOutlet UITextField *messageField;
@property (nonatomic,retain) NSString *chatWithUser;
@property (nonatomic,retain) IBOutlet UITableView *chatTableView;

- (IBAction) sendMessage;

@end

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在这两个视图控制器之间传递数据的正确方式是什么？我的变量保持为零。

问题是您正在实例化一个新的ChatViewController，而这不是segue将要使用的。您应该从segue的destinationViewController属性获取该控制器

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if([[segue identifier] isEqualToString:@"chat"]) {
        NSString *userName = (NSString *) [toUsersArray objectAtIndex:[self.chatsTableView indexPathForSelectedRow].row];

    ChatViewController *chatViewController = segue.destinationViewController;
    chatViewController.chatWithUser = username;
    }
}

---

问题是您正在实例化一个新的ChatViewController，而这不是segue将要使用的。您应该从segue的destinationViewController属性获取该控制器

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if([[segue identifier] isEqualToString:@"chat"]) {
        NSString *userName = (NSString *) [toUsersArray objectAtIndex:[self.chatsTableView indexPathForSelectedRow].row];

    ChatViewController *chatViewController = segue.destinationViewController;
    chatViewController.chatWithUser = username;
    }
}

---

//获取对目标视图控制器的引用

---

ChatViewController*ChatViewController=[segue destinationViewController]

//获取对目标视图控制器的引用

ChatViewController*ChatViewController=[segue destinationViewController]