如何在呈现之前设置根视图控制器的属性？

Posted 2023-03-22

【中文标题】如何在呈现之前设置根视图控制器的属性？

【英文标题】：How to set properties of a root view controller before being presented?

【发布时间】：2015-09-12 08:23:17

【问题描述】：

我在storyboard 中有某个UINavigationController 我从另一个视图控制器模态呈现：

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UINavigationController *myNavController = [storyboard instantiateViewControllerWithIdentifier:@"myNavController"];
[self presentViewController:myNavController animated:YES completion:nil];

这个导航控制器在storyboard 中设置了另一个UIViewController 作为它的根视图控制器。我想在这个根视图控制器显示之前为其设置一些属性，但我尝试了这个：

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UINavigationController *myNavController = [storyboard instantiateViewControllerWithIdentifier:@"myNavController"];
[self presentViewController:myNavController animated:YES completion:nil];
 MyRootViewController *myRootViewController = [storyboard instantiateViewControllerWithIdentifier:@"myRootViewController"];
[myRootViewController setSelectedItem:selectedItem];
[myRootViewController setDelegate:self];

但是当我尝试设置它的属性时，似乎还没有加载根视图控制器...

我怎么能这样做？谢谢

【参考方案1】：

如果你调试过，你会发现MyRootViewController *myRootViewController = [storyboard instantiateViewControllerWithIdentifier:@"myRootViewController"]; 制作的myRootViewController并不是myNavController真正的rootViewController。

这个方法-instantiateViewControllerWithIdentifier: 只是给你一个全新的 UIViewController 实例。

所以，如果你想获得真正的 rootViewController，只需将其替换为以下内容：

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UINavigationController *myNavController = [storyboard instantiateViewControllerWithIdentifier:@"myNavController"];

 MyRootViewController *myRootViewController = myNavController.viewControllers[0];
[myRootViewController setSelectedItem:selectedItem];
[myRootViewController setDelegate:self];

[self presentViewController:myNavController animated:YES completion:nil];