点击 UITabBarItem 像 Instagram 和 Twitter 一样滚动到顶部

Question

我在使用此功能时遇到问题，我想获得一些帮助。

我的层次结构是TabBarController -> Navigation Controller -> TableViewController

我想要的是，如果您在当前选项卡上并且向下滚动，您将能够点击当前视图的 UITabBarItem，您将被滚动回顶部，例如 Instagram 和 Twitter。

我在这里尝试了很多东西：

Older Question

但遗憾的是，没有一个答案对我有用。

对于这种方式的任何帮助，我将不胜感激， 提前谢谢！

这是我的 TableView`控制器的代码：

import UIKit

class BarsViewController: UITableViewController,UISearchResultsUpdating,UISearchBarDelegate,UISearchDisplayDelegate,UITabBarControllerDelegate{

//TableView Data & non related stuff....

override func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        self.searchController.searchBar.resignFirstResponder()
        self.searchController.searchBar.endEditing(true)
    }

 func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        let tabBarIndex = tabBarController.selectedIndex
        if tabBarIndex == 0 {

            let indexPath = IndexPath(row: 0, section: 0)
            let navigVC = viewController as? UINavigationController
            let finalVC = navigVC?.viewControllers[0] as? BarsViewController
            finalVC?.tableView.scrollToRow(at: indexPath as IndexPath, at: .top, animated: true)

        } 
    }

}

TabBarController.Swift 代码（代码不起作用）：

import UIKit

class TabBarController: UITabBarController,UITabBarControllerDelegate {

       override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
    self.delegate = self
}


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
        guard let viewControllers = viewControllers else { return false }
        if viewController == viewControllers[selectedIndex] {
            if let nav = viewController as? UINavigationController {
                guard let topController = nav.viewControllers.last else { return true }
                if !topController.isScrolledToTop {
                    topController.scrollToTop()
                    return false
                } else {
                    nav.popViewController(animated: true)
                }
                return true
            }
        }

        return true
    }

}
extension UIViewController {
    func scrollToTop() {
        func scrollToTop(view: UIView?) {
            guard let view = view else { return }

            switch view {
            case let scrollView as UIScrollView:
                if scrollView.scrollsToTop == true {
                    scrollView.setContentOffset(CGPoint(x: 0.0, y: -scrollView.contentInset.top), animated: true)
                    return
                }
            default:
                break
            }

            for subView in view.subviews {
                scrollToTop(view: subView)
            }
        }

        scrollToTop(view: view)
    }

    var isScrolledToTop: Bool {
        for subView in view.subviews {
            if let scrollView = subView as? UIScrollView {
                return (scrollView.contentOffset.y == 0)
            }
        }
        return true
    }

}

Answer 1

给你，这应该可以：

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
    guard let viewControllers = viewControllers else { return false }
    if viewController == viewControllers[selectedIndex] {
        if let nav = viewController as? ZBNavigationController {
            guard let topController = nav.viewControllers.last else { return true }
            if !topController.isScrolledToTop {
                topController.scrollToTop()
                return false
            } else {
                nav.popViewController(animated: true)
            }
            return true
        }
    }

    return true
}

然后……

extension UIViewController {
    func scrollToTop() {
        func scrollToTop(view: UIView?) {
            guard let view = view else { return }

            switch view {
            case let scrollView as UIScrollView:
                if scrollView.scrollsToTop == true {
                    scrollView.setContentOffset(CGPoint(x: 0.0, y: -scrollView.contentInset.top), animated: true)
                    return
                }
            default:
                break
            }

            for subView in view.subviews {
                scrollToTop(view: subView)
            }
        }

        scrollToTop(view: view)
    }

    // Changed this

    var isScrolledToTop: Bool {
        if self is UITableViewController {
            return (self as! UITableViewController).tableView.contentOffset.y == 0
        }
        for subView in view.subviews {
            if let scrollView = subView as? UIScrollView {
                return (scrollView.contentOffset.y == 0)
            }
        }
        return true
    }
}

这个函数有一点额外的，如果UIViewController已经在顶部，它会弹出到前一个控制器

Answer 2

在您的 TabViewController 中尝试此代码：

func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
    let tabBarIndex = tabBarController.selectedIndex
    if tabBarIndex == 0 {

        let indexPath = NSIndexPath(row: 0, section: 0)
        let navigVC = viewController as? UINavigationController
        let finalVC = navigVC?.viewControllers[0] as? YourVC
        finalVC?.tableView.scrollToRow(at: indexPath as IndexPath, at: .top, animated: true)

    } 
}

另外，你的 TabViewController 应该继承自 UITabBarControllerDelegate

最终代码：

import UIKit

class tabViewController: UITabBarController, UITabBarControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.delegate = self
        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        let tabBarIndex = tabBarController.selectedIndex
        if tabBarIndex == 0 {

            let indexPath = NSIndexPath(row: 0, section: 0)
            let navigVC = viewController as? UINavigationController
            let finalVC = navigVC?.viewControllers[0] as? YourVC
            finalVC?.tableView.scrollToRow(at: indexPath as IndexPath, at: .top, animated: true)

        } 
    }


}

记得更改 tabBarIndex 并在 viewDidLoad 中设置 self.delegate = self

Answer 3

您只需使用以下代码创建一个文件TabBarViewController：

class TabBarController: UITabBarController, UITabBarControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        self.delegate = self
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
        guard let viewControllers = viewControllers else { return false }
        if viewController == viewControllers[selectedIndex] {
            if let nav = viewController as? UINavigationController {
                guard let topController = nav.viewControllers.last else { return true }
                if !topController.isScrolledToTop {
                    topController.scrollToTop()
                    return false
                } else {
                    nav.popViewController(animated: true)
                }
                return true
            }
        }

        return true
    }
}

extension UIViewController {
    func scrollToTop() {
        func scrollToTop(view: UIView?) {
            guard let view = view else { return }

            switch view {
            case let scrollView as UIScrollView:
                if scrollView.scrollsToTop == true {
                    scrollView.setContentOffset(CGPoint(x: 0.0, y: -scrollView.contentInset.top), animated: true)
                    return
                }
            default:
                break
            }

            for subView in view.subviews {
                scrollToTop(view: subView)
            }
        }

        scrollToTop(view: view)
    }

    var isScrolledToTop: Bool {
        if self is UITableViewController {
            return (self as! UITableViewController).tableView.contentOffset.y == 0
        }
        for subView in view.subviews {
            if let scrollView = subView as? UIScrollView {
                return (scrollView.contentOffset.y == 0)
            }
        }
        return true
    }
}

然后在你的故事板中，像这样设置自定义类TabBarController：

Answer 4

很好的例子！我也尝试了一些东西，我想我们的委托的这一小段代码就是我们所需要的：

extension AppDelegate: UITabBarControllerDelegate {

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
    // Scroll to top when corresponding view controller was already selected and no other viewcontrollers are pushed
    guard tabBarController.viewControllers?[tabBarController.selectedIndex] == viewController,
          let navigationController = viewController as? UINavigationController, navigationController.viewControllers.count == 1,
          let topViewController = navigationController.viewControllers.first,
          let scrollView = topViewController.view.subviews.first(where: { $0 is UIScrollView }) as? UIScrollView else {
        return true
    }

    scrollView.scrollRectToVisible(CGRect(origin: .zero, size: CGSize(width: 1, height: 1)), animated: true)
    return false
}

}

Answer 5

我只需要实现它，然后惊讶地发现它并不像我想象的那么容易。这就是我实现它的方式：

关于我的应用程序设置的一些注意事项

• MainTabBarcontroller 是我们的根视图控制器，我们通常从 UISharedApplication 访问它。
• 我们的导航结构是 MainTabBarController -> Nav Controller -> Visible View Controller

我发现实现此功能的主要问题是，如果我已经在标签栏的第一个屏幕上，我只想滚动到顶部，但是一旦您尝试从 tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) 进行此检查，您已经失去了引用在您点击它之前可见的视图控制器。在切换选项卡时比较视图控制器也是一个问题，因为可见视图控制器可能位于另一个选项卡中。

所以我在我的 TabBar 类中创建了一个属性来保存对 previousTopVC 的引用，并创建了一个协议来帮助我从当前可见的 VC 中设置此属性。

protocol TopScreenFindable {
    func setVisibleViewController()
}

extension TopScreenFindable where Self: UIViewController {
    func setVisibleViewController() {
        guard let tabController = UIApplication.shared.keyWindow?.rootViewController as? MainTabBarController else { return }
        tabController.previousTopVC = self
    }
}

然后我从视图控制器的 viewDidAppear 调用符合此协议和 setVisibleViewController 并且现在在任何屏幕出现时都引用了以前的可见 VC。

我为我的 MainTabBarController 类创建了一个委托

protocol MainTabBarDelegate: class {
    func firstScreenShouldScrollToTop()
}

然后从 UITabBarControllerDelegate 方法调用它

func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        guard let navController = viewController as? UINavigationController, let firstVC = navController.viewControllers.first, let previousVC = previousTopController else { return }
        if firstVC == previousVC {
            mainTabBarDelegate?.firstScreenShouldScrollToTop()
        }
    } 

并且在第一个视图中控制器符合 MainTabBarDelegate

extension FirstViewController: MainTabBarDelegate {
    func firstScreenShouldScrollToTop() {
        collectionView.setContentOffset(CGPoint(x: 0, y: collectionView.contentInset.top), animated: true)
    }

我在 FirstViewController 的 viewDidAppear 上设置了tabBar.mainTabBarDelegate = self，这样每次屏幕出现时都会设置委托。如果我在 viewDidLoad 上执行此操作，则切换选项卡时将无法正常工作。

我不喜欢我的方法的几件事。

• 在我的视图控制器中引用标签栏，以便它可以将自己设置为其委托。
• 使应用中的每个相关屏幕都符合TopScreenFindable 协议