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。

我的等级是 TabBarController -> Navigation Controller -> TableViewController

我想要的是，如果您在当前选项卡上并向下滚动，您将能够点击当前视图的 UITabBarItem，然后您将滚动回到顶部，例如 Instagram 和 Twitter 所做的.

我在这里尝试了很多东西:

Older Question

但遗憾的是，没有一个答案适合我。

对于这种方式的任何帮助，我将不胜感激，提前致谢！

这是我的 TableView`controller 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（代码无效）：

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

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)

    } 
}

此外，您的 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)

        } 
    }


}

记得修改tabBarIndex，在viewDidLoad

中设置self.delegate = self

Answer 2

给你，这应该有效：

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
    }
}

这个函数有一些额外的东西，所以如果 UIViewController 已经在顶部，它将弹出到前一个控制器

Answer 3

我只需要实现它，并惊讶地发现它并不像我想象的那么容易。我是这样实现的：

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

我在实现这个过程中发现的主要问题是，如果我已经在标签栏的第一个屏幕上，我只想滚动到顶部，但是一旦你尝试从 tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) 进行检查，你'在您点击它之前，您已经丢失了对可见视图控制器的引用。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 class 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设置属性可见 VC。

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 中调用了 conformed to this protocol 和 setVisibleViewController，现在在任何屏幕出现时都有对先前可见 VC 的引用。

我为我的 MainTabBarController 创建了一个委托 class

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()
        }
    }

并且在第一个视图控制器中符合 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，以便每次出现屏幕时都设置委托。如果我在 viewDidLoad 上执行它，则在切换选项卡时将不起作用。

有几点我不喜欢我的方法。

在我的视图控制器中引用选项卡栏，以便它可以将自己设置为它的委托。
使应用程序中的每个相关屏幕都符合 TopScreenFindable 协议

Answer 4

您只需使用以下代码创建文件 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 class TabBarController :

Answer 5

很好的例子！我也尝试了一些东西，我想我们的委托的这段小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: { [=10=] is UIScrollView }) as? UIScrollView else {
        return true
    }

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

}

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

Tap UITabBarItem To Scroll To Top Like Instagram and Twitter

ios

swift

uitableview

scrolltop

uitabbaritem

这是我的 TableView`controller 代码：

TabBarController.Swift 代码（代码无效）：