在选项卡之间切换时如何创建交叉溶解动画

Question

如何在标签之间切换时执行的标签控制器类中编写简单的交叉溶解动画。

以下是显示此类动画的应用示例。

我对自定义过渡动画还很陌生，我知道它必须在 didSelect 中进行

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

}

更新

我似乎有些困惑：

我创建了一个名为 TabBarClass.swift 的新 Swift 文件

我在里面添加了如下代码：

    class MyFadeTransition: NSObject, UIViewControllerAnimatedTransitioning {
        func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
            if let fromVC = transitionContext.viewController(forKey: .from), let toVC = transitionContext.viewController(forKey: .to) {
                toVC.view.frame = fromVC.view.frame
                toVC.view.alpha = 0
                fromVC.view.alpha = 1
                transitionContext.containerView.addSubview(fromVC.view)
                transitionContext.containerView.addSubview(toVC.view)

                UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                    toVC.view.alpha = 1
                }) { (finished) in
                    transitionContext.completeTransition(finished)
                }
            }
        }

        func animationEnded(_ transitionCompleted: Bool) {
            // no-op
        }

        func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
            return 0.3
        }
    }


**And in the AppDelegate I added:**

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
            let fade = MyFadeTransition()
            return fade
        }

What is the issue?

更新 2

这就是我的 AppDelegate 的编写方式：

import UIKit

@UIApplicationMain


class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    var tabBarController: UITabBarController!

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {


        let tab = window!.rootViewController as! UITabBarController
        tab.delegate = self


        return true
    }



    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }


}
extension AppDelegate: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        let fade = MyFadeTransition()

        return fade
    }
}

Answer 1

利用UITabBarControllerDelegate方法：

func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning?

大部分工作都在符合UIViewControllerAnimatedTransitioning的类中。

这是一个交叉淡入淡出两个控制器的实现。

MyFadeTransition.swift：

import UIKit

class MyFadeTransition: NSObject, UIViewControllerAnimatedTransitioning {
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        if let fromVC = transitionContext.viewController(forKey: .from), let toVC = transitionContext.viewController(forKey: .to) {
            toVC.view.frame = fromVC.view.frame
            toVC.view.alpha = 0
            fromVC.view.alpha = 1
            transitionContext.containerView.addSubview(fromVC.view)
            transitionContext.containerView.addSubview(toVC.view)

            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                toVC.view.alpha = 1
            }) { (finished) in
                transitionContext.completeTransition(finished)
            }
        }
    }

    func animationEnded(_ transitionCompleted: Bool) {
        // no-op
    }

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.3
    }
}

您的代码中的某些内容必须是标签栏控制器的delegate。设置它，然后在该类中实现委托方法。

func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    let fade = MyFadeTransition()
    return fade
}

请注意，同样的MyFadeTransition 类可以与UINavigationController 一起使用。 UINavigationControllerDelegate 具有相同的基本方法，因此您可以为标签栏控制器和导航控制器重用转换类。

假设您的标签栏控制器是您应用的根视图控制器，您可以将以下代码添加到您的 AppDelegate 的 didFinishLaunchingWithOptions：

let tab = window!.rootViewController as! UITabBarController
tab.delegate = self

然后添加：

extension AppDelegate: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        let fade = MyFadeTransition()

        return fade
    }
}

到 AppDelegate.swift。