ios - 如何像 Facebook 一样向下滚动后从顶部滚动 - Swift 4.2

Question

我想实现像 Facebook 应用程序一样的滚动功能，如果向下滚动页面，请点击选项卡栏项目，然后点击相同的选项卡栏项目，它会从顶部开始滚动。

这是我的代码 -

override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {

        let indexOfTab = tabBar.items?.index(of: item)
        if indexOfTab == 0{
            let feed = HomeFeedViewController()
            feed.scrollToTop()
            print("pressed tabBar: \(String(describing: indexOfTab))")
        }else if indexOfTab == 1{
            print("pressed tabBar: \(String(describing: indexOfTab))")

        }else if indexOfTab == 2{
            print("pressed tabBar: \(String(describing: indexOfTab))")

        }else if indexOfTab == 3{
            let feed = QueueViewController()
            print("pressed tabBar: \(String(describing: indexOfTab))")

        }else if indexOfTab == 4{
            print("pressed tabBar: \(String(describing: indexOfTab))")

        }

    }


 func scrollToTop(){

        feedsTableView.setContentOffset(.zero, animated: true)
    }

Answer 1

对于 swift

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: self.view)
    }
}

使用

var previousController: UIViewController?

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {

        //when user is in FeedViewController and scroll at last record and want to
        if previousController == viewController {
            if let navVC = viewController as? UINavigationController, let vc = navVC.viewControllers.first as? HomeViewController {

                if vc.isViewLoaded && (vc.view.window != nil) {
                    vc.scrollToTop()
                }
                print("same")
            }
        }
        else{
            print("No same")
        }

        previousController = viewController
        return true;
    }