如何检查当前viewController或根viewController？

Question

我已经用UITabBarDelegate设置了我的class，并实现了它的method didSelectItem来检测某个tabBar项何时被按下。效果很好。在每个tabBar项中，我有一个containerView，如果用户没有登录，它可以显示“您必须登录”-page，另一个containerView表示嵌入在navigationController中的viewControllers。

我想跟踪当前tab项中显示的viewController，和/或该tab的root viewController。

我已经尝试了许多不同的方法，但大多数方法都返回nil，或者我无法让它工作。我认为整个container的情况让它更难处理。

它看起来像这样：

@interface MyTabBarController () <UITabBarDelegate> 

- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item {

    NSUInteger indexOfTab = [[tabBar items] indexOfObject:item];

    switch (indexOfTab) {
        case 0: {
            NSLog(@"?PRESSIIING %lu", (unsigned long)[[tabBar items] indexOfObject:item]);
            break;
        }
        case 1: {
           NSLog(@"?PRESSIIING %lu", (unsigned long)[[tabBar items] indexOfObject:item]);
           break;
        }
        case 2: {
           NSLog(@"?PRESSIIING %lu", (unsigned long)[[tabBar items] indexOfObject:item]);

//These return nil
            NSLog(@"?AAAAAA %@", ((UINavigationController*)_appD.window.rootViewController).visibleViewController);
            NSLog(@"?AAAAAA %@", ((UITabBarController*)_appD.window.rootViewController).selectedViewController);
            NSLog(@"?AAAAAA %@", self.navigationController.topViewController);
            NSLog(@"?AAAAAA %@", self.navigationController.visibleViewController);

//This returns with a value, but can't get it to work with conditionals, that is, when I'm in root, the else is triggered
            NSLog(@"?AAAAAA %@", self.tabBar.window.rootViewController);

            if(!self.tabBar.window.rootViewController) {
                NSLog(@"???THIS IS NOT ROOT???");

            }else {
                NSLog(@"???this is ROOT???");
            }

// This returns nil
            ((UINavigationController*)_appD.window.rootViewController).visibleViewController;
            ((UITabBarController*)_appD.window.rootViewController).selectedViewController;

            //Doesn't work
            if([self.navigationController.viewControllers[0] isKindOfClass:[ExperiencesListViewController class]]) {
                           NSLog(@"?IS KIND OF CLASS LIST");
                       }
                       if([self.navigationController.viewControllers[0].childViewControllers isKindOfClass:[ExperiencesContainerViewController class]]) {
                           NSLog(@"?IS KIND OF CLASS CONTAINER");
                     }
           break;
       }
        case 3: {
           NSLog(@"?PRESSIIING %lu", (unsigned long)[[tabBar items] indexOfObject:item]);
           break;
       }
        case 4: {
           NSLog(@"?PRESSIIING %lu", (unsigned long)[[tabBar items] indexOfObject:item]);
           break;
       }
        default:
            break;
    }
}

So, what else can I try? Seems like I have to use `self.tabBar.window.rootViewController` in some way, no?

***EDIT*** 
Oh, and I have tried the `tabBarController` delegate but that doesn't trigger. Also, the `tabBar` is constructed programmatically if that helps.

Answer 1

很抱歉，没有正确阅读您的问题。这是我建议你做的。

所有这些您有兴趣跟踪的视图控制器:您应该让它们从它们的-viewDidAppear: (或-viewWillAppear:)方法中发送一个自定义通知。然后让您的ApolloTabBarController对象注册该通知。当它收到通知时，您可以存储对视图控制器的引用。该引用将始终指向活动视图控制器。

在您的单个视图控制器中，执行类似以下操作：

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];

    [nc postNotificationName:@"XYZViewControllerDidBecomeActiveNotification"
                      object:self];
}

当然，您可能希望使用某种常量作为通知名称。

在您的ApolloTabBarController类中，注册XYZViewControllerDidBecomeActiveNotification并实现如下内容：

- (void)viewControllerDidBecomeActive:(NSNotification *)notification
{
    self.activeViewController = [notification object];
}

我希望这对你有帮助！

Answer 2

在为每个选项卡设置每个视图控制器时，将UITabBarItem的tag属性设置为与选项卡栏的viewControllers数组中的视图控制器的索引相对应。

UIViewController* myFirstVC = [[UIViewController alloc] init];
UIViewController* mySecondVC = [[UIViewController alloc] init];

// "self" is your ApolloTabBarController.
[self setViewControllers:@[myFirstVC, mySecondVC]];

myFirstVC.tabBarItem = 
    [[UITabBarItem alloc] initWithTitle:@"First" image:nil tag:0];

mySecondVC.tabBarItem = 
    [[UITabBarItem alloc] initWithTitle:@"Second" image:nil tag:1];

然后，您将能够获取对视图控制器的引用。

// In your example, your ApolloTabBarController acts as its own delegate.
- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item
{
    UIViewController* activeVC = 
        [[self viewControllers] objectAtIndex:[item tag]];
}