在呈現之前如何設置根視圖控制器的屬性？

Question

我在storyboard有一個UINavigationController ，是我從另一個視圖控制器以模態形式呈現的：

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

此導航控制器已將另一個UIViewController設置為storyboard UIViewController中的根視圖控制器。 我想在顯示該根視圖控制器之前為其設置一些屬性，但是我嘗試了以下操作：

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];

但是當我嘗試設置它的屬性時，似乎尚未加載根視圖控制器。

我該怎么辦？ 謝謝

Answer 1

如果已調試，則將找到myRootViewController制造的MyRootViewController *myRootViewController = [storyboard instantiateViewControllerWithIdentifier:@"myRootViewController"]; 不是myNavController的實際rootViewController。

此方法-instantiateViewControllerWithIdentifier:只是給您一個全新的UIViewController實例。

因此，如果要獲取真正的rootViewController，只需將其替換為以下內容：

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];