navigationController.navigationItem vs navigationItem [英] navigationController.navigationItem vs navigationItem

问题描述

好奇，为什么设置 self.navigationItem = ... 有效，但 self.navigationController.navigationItem 失败？这同样适用于 self.toolbarItems vs self.navigationController.toobarItems 。

Just curious, why setting self.navigationItem = ... works, but self.navigationController.navigationItem fails? The same applies for self.toolbarItems vs self.navigationController.toobarItems.

何时使用 self.navigationController.navigationItem ？

也许你会说，他们指向不同的东西。但为什么 self.navigationController.navigationBarHidden = YES 隐藏了导航栏。是不是意味着 self.navigationController.navigationItem 指向我想要的酒吧？

Maybe you will say, they point to different things. but why self.navigationController.navigationBarHidden = YES the navigation bar is hidden. doesn't it means self.navigationController.navigationItem point to the bar i wanted?

推荐答案

类 UIViewController 有一个属性 navigationItem 。

对于所有子类也是如此，无论它是 UICollectionViewController ， UITableViewController ， UINavigationViewController 或任何自定义子类。

This is true of all the subclasses too whether it is a UICollectionViewController, UITableViewController, UINavigationViewController or any custom subclass.

当由 UINavigationController 导航时controller将创建此属性，因此每个视图控制器都有自己的 navigationItem 。如果你没有从导航控制器中显示它，那么navigationItem是零。

When presented by a UINavigationController the nav controller will create this property and so each view controller gets its own navigationItem. If you do not present it from a navigation controller then the navigationItem is nil.

现在，使用 UINavigationController 你很可能使用它作为您的初始视图控制器。因此，导航控制器不会被另一个导航控制器呈现，其 navigationItem 属性为零。

Now, with a UINavigationController you are more than likely using this as your initial view controller. Therefore, the navigation controller is NOT being presented by another navigation controller and its navigationItem property is nil.

导航bar略有不同，因为这是另一种方式。

The navigation bar is slightly different as this is managed the other way around.

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