如何檢查當前視圖控制器或根視圖控制器？

Question

我已經使用UITabBarDelegate設置了我的class並實現了它的method didSelectItem以檢測何時按下某個tabBar項目。 效果很好。 在每個tabBar項目中，我有一個containerView ，如果用戶未登錄，它可以顯示“您必須登錄”頁面，另一個containerView顯示嵌入在navigationController viewControllers 。

我想跟蹤當前tab項中顯示的viewController和/或該tab的root viewController 。

我嘗試了許多不同的方法，但大多數都返回 nil 或者我無法讓它工作。 我認為整個container情況使它更難處理。

它看起來像這樣：

@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

很抱歉沒有正確閱讀您的問題。 這是我建議你做的。

您有興趣跟蹤的所有這些視圖控制器：您應該讓他們從-viewDidAppear:或-viewWillAppear:方法中發送自定義通知。 然后讓您的 ApolloTabBarController 對象注冊該通知。 當它收到通知時，您可以存儲對視圖控制器的引用。 該引用將始終指向活動視圖控制器。

在您的各個視圖控制器中，執行以下操作：

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

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

當然，您可能希望對通知名稱使用某種常量。

在您的 ApolloTabBarController 類中，注冊XYZViewControllerDidBecomeActiveNotification並實現如下內容：

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

我希望這有幫助！

Answer 2

當您為每個選項卡設置每個視圖控制器時，將UITabBarItem的tag屬性設置為對應於選項卡欄viewControllers數組中視圖控制器的索引。

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，您將能夠獲取對視圖控制器的引用。

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