iPhone - topViewController和其他表单之间的区别 [英] iPhone - difference between topViewController and other forms

问题描述

我正在使用基于NavigationControl的应用程序的代理。

当我尝试使用

<时访问rootViewController pre> RootViewController * rootViewController =（RootViewController *）[navigationController topViewController];


运行一个方法，崩溃，说rootViewController上的方法是未知。

当我使用此访问rootViewController时

  RootViewController * rootViewController =（RootViewController） *）[navigationController.viewControllers objectAtIndex：0]; 
  

它有效。

哪一个对象是第一行访问？

谢谢

解决方案

导航控制器的topViewController 表示堆栈顶部的视图控制器。索引 0 是底部。 topViewController 只有当一个视图控制器在堆栈上时才是索引 0 的对象。如果你有多个，那就不一样了。我猜这是因为它崩溃，因为 topViewController 不知道如何响应用于 RootViewController的消息实例。

I am on a delegate of a NavigationControl based app.

when I try to access the rootViewController using

RootViewController *rootViewController = (RootViewController *)[navigationController topViewController];

to run a method, it crashes, saying the method is "unknown" on the rootViewController.

When I access the rootViewController using this

RootViewController *rootViewController = (RootViewController *)[navigationController.viewControllers objectAtIndex:0];

it works.

Which object is the first line accessing?

thanks

解决方案

topViewController of a navigation controller represents the view controller at the top of the stack. Index 0 is the bottom. topViewController is the object at index 0 only when one view controller is on the stack. If you have more than one, it is not the same. I am guessing that it is the case as it's crashing because the topViewController doesn't know how to respond to messages intended for a RootViewController instance.

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