访问父视图控制器（自定义）属性

问题描述

我编写了一个 UITabBarController 子类（名为 MainViewController ）并添加了一些实例变量，特别是一个类型地点。 MainViewController 的每个选项卡都需要访问 MainViewController 的场地变量。在第一个选项卡中，一个名为 HomeViewController 的 UIViewController 子类，我写了 viewDidLoad 方法并试图用两个输出到NSLog ...

I have written a UITabBarController subclass (called MainViewController) and added a few instance variables, specifically a venue of type Venue. Each tab of the MainViewController needs to access the venue variable of the MainViewController. In the first tab, a UIViewController subclass named HomeViewController, I wrote my viewDidLoad method and tried to output to NSLog with both...

NSLog(@"%@", self.parentViewController.venue.name);

和

NSLog(@"%@", self.tabBarController.venue.name);

但是XCode给出错误

But XCode gives the error

error: request for member 'venue' in something not a structure or union

我可以从 MainViewController 中访问场地属性，所以在那里排除了错误。 iPhone模拟器确实看到 self.parentViewController 和 self.tabBarController 作为 MainViewController的实例。该行......

I can access the venue property from within MainViewController just fine so have ruled out an error there. The iPhone simulator does see both self.parentViewController and self.tabBarController as an instance of MainViewController. The line...

NSLog(@"%@", self.tabBarController);

输出......

2009-06-05 17:54:46.502 Venue[29729:20b] <MainViewController: 0x536600>

因为它被视为 MainViewController 实例，我怀疑使用铸造会有所帮助。我唯一的另一个选择是使用场地副本初始化 HomeViewController ，或者我只是做了' self.parentViewController.venue的完全错误。名称'？谢谢，Rob

Since it's seen as a MainViewController instance, I doubt using casting would help. Is my only other option to initialize the HomeViewController with a copy of the venue or am I just doing something completely wrong with 'self.parentViewController.venue.name'? Thanks, Rob

推荐答案

你做错了什么。 parentViewController 被声明为 UIViewController 。 NSLog 由于多态性的奇迹，它输出它的真实类型。

You're doing something completely wrong. parentViewController is declared as a UIViewController. NSLoging it outputs its real type due to the wonders of polymorphism.

UIViewController 没有 Venue 成员。您的 MainViewController 可以。事实上，铸造它是正确的答案。确保也导入 MainViewController.h 。

UIViewController doesn't have a Venue member. Your MainViewController does. Casting it is, in fact, the right answer. Make sure to import MainViewController.h as well.

#import "MainViewController.h"
[...]
NSString *name = ((MainViewController *)self.parentViewController)).venue.name;

当然，还要确保场地被声明为MainViewController的 @property ， name 是 @property Venue 。

Also make sure, of course, that venue is declared as a @property of MainViewController, and name is a @property of Venue.

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