在 TabBarController 中显示模态视图控制器

Question

我有一个主要的tabBarController，并且想在点击某个tabBarItem 时显示一个viewController modally。

我正在将viewControllers 加载到我的tabBarController 中...

func setupViewControllers() {
    self.tabBar.isHidden = false

    if let firstVC = storyboard?.instantiateViewController(withIdentifier: "first") as? FirstViewController, let secondVC = storyboard?.instantiateViewController(withIdentifier: "second") as? SecondViewController, let thirdVC = storyboard?.instantiateViewController(withIdentifier: "third") as? ThirdViewController, let fourthVC = storyboard?.instantiateViewController(withIdentifier: "fourth") as? FourthViewController, let fifthVC = storyboard?.instantiateViewController(withIdentifier: "fifth") as? FifthViewController {

        let firstNavController = UINavigationController(rootViewController: firstVC)
        let secondNavController = UINavigationController(rootViewController: secondVC)
        let fourthNavController = UINavigationController(rootViewController: fourthVC)
        let fifthNavController = UINavigationController(rootViewController: fifthVC)

        firstNavController.tabBarItem.image = image
        secondNavController.tabBarItem.image = image
        fourthNavController.tabBarItem.image = image
        fifthNavController.tabBarItem.image = image     
        thirdVC.tabBarItem.image = image

        tabBar.tintColor = nil

        //Load tabBar viewControllers
        viewControllers = [homeNavController, postNavController, plusMenuVC, meetupNavController, profileNavController]
    }
}

然后我将tabBarViewController 与UITabBarControllerDelegate 一致以调用该方法...

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
    if tabBarController.selectedIndex == 2, let thirdVC = viewController as? ThirdViewController {
        thirdVC.modalPresentationStyle = .overFullScreen
        thirdVC.modalTransitionStyle = .crossDissolve
        present(thirdVC, animated: true, completion: nil)
        return false
    } else { return true }
}

然而，上述内容永远不会被触发。我尝试设置viewDidLoad

self.delegate = self

我尝试将根导航控制器及其祖先 tabBarController 委托设置为 self。

似乎没有任何工作，我希望有人可以指导我，因为我无法调试并找到现有的解决方案......

更新 所以我创建了一个dummyThirdVC 来替换setupViewControllers() 函数中的thirdVC。在dummyThirdVC 中，我符合UITabBarControllerDelegate 并在viewDidLoad 中设置self.tabBarController.delegate = self。然后我把delegate方法输入到这个dummyThirdVC中，在这个delegate方法里面，我实例化了真正的thirdVC来呈现。

delegate 方法终于正确触发了，但我现在的问题是，dummyThirdVC 及其视图必须首先加载并出现，然后才能设置和触发delegate。

我怎么能不显示dummyThirdVC 并立即显示实例化的真实thirdVC？我在setupViewControllers 函数中尝试过dummyThirdVC.viewDidLoad() 无济于事......

Answer 1

我相信你的支票是错的。您正在检查 selectedIndex 是否为 2，但 selectedIndex 的值将始终是实际选项卡栏的选定索引，而不是将要选择的索引，因此您基本上永远不会到达selectedIndex 为 2。

你也不能展示一个已经处于活动状态的视图控制器，并且thirdVC 在你的tabBar 中已经处于活动状态，因此你会得到一个错误。一种解决方法是使用 viewController 作为标签栏中图像和标题的占位符，并实例化另一个用于呈现。

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
    if viewController is ThirdViewController {
        let vcToPresent = storyboard?.instantiateViewController(withIdentifier: "third") as? ThirdViewController
        vcToPresent.modalPresentationStyle = .overFullScreen
        vcToPresent.modalTransitionStyle = .crossDissolve
        present(vcToPresent, animated: true, completion: nil)
        return false
    }
    return true
}