让 AVPlayer 的 SwiftUI 包装器在视图消失时暂停

Question

TL;DR

似乎无法使用绑定来告诉包装 AVPlayer 停止 — 为什么不呢？ Vlad 中的 "one weird trick" 对我有用，没有状态和绑定，但为什么呢？

另请参阅

我的问题类似于 this one，但发帖人想要包装一个 AVPlayerViewController 而我想以编程方式控制播放。

This guy 也想知道什么时候调用了 updateUIView()。

发生了什么（如下所示的控制台日志。）

使用此处所示的代码，

用户点击 "Go to Movie"
- MovieView 出现并且视频播放
- 这是因为 updateUIView(_:context:) 被调用
用户点击 "Go back Home"
- HomeView重现
- 播放停止
- 再次调用 updateUIView。
- 查看控制台日志 1
但是...删除###行，然后
- 即使主视图returns
- updateUIView 到达时被调用但离开时不被调用
- 查看控制台日志 2
如果您取消注释 %%% 代码（并注释掉它前面的内容）
- 你得到的代码我认为在逻辑上和惯用上都是正确的 SwiftUI...
- ...但是 "it doesn't work"。 IE。视频在到达时播放，但在离开时继续播放。
- 查看控制台日志 3

代码

我做使用@EnvironmentObject所以是一些状态共享正在进行。

主要内容视图（此处无争议）：

struct HomeView: View {
    @EnvironmentObject var router: ViewRouter

    var body: some View {
        ZStack() {  // +++ Weird trick ### fails if this is Group(). Wtf?
            if router.page == .home {
                Button(action: { self.router.page = .movie }) {
                    Text("Go to Movie")
                }
            } else if router.page == .movie {
                MovieView()
            }
        }
    }
}

它使用其中之一（仍然是常规声明式 SwiftUI）：

struct MovieView: View {
    @EnvironmentObject var router: ViewRouter
    // @State private var isPlaying: Bool = false  // %%%

    var body: some View {
        VStack() {
            PlayerView()
            // PlayerView(isPlaying: $isPlaying) // %%%
            Button(action: { self.router.page = .home }) {
                Text("Go back Home")
            }
        }.onAppear {
            print("> onAppear()")
            self.router.isPlayingAV = true
            // self.isPlaying = true  // %%%
            print("< onAppear()")
        }.onDisappear {
            print("> onDisappear()")
            self.router.isPlayingAV = false
            // self.isPlaying = false  // %%%
            print("< onDisappear()")
        }
    }
}

现在我们进入 AVKit 特定的内容。我使用 Chris Mash.

描述的方法

前面提到的PlayerView，wrappER:

struct PlayerView: UIViewRepresentable {
    @EnvironmentObject var router: ViewRouter
    // @Binding var isPlaying: Bool     // %%%

    private var myUrl : URL?   { Bundle.main.url(forResource: "myVid", withExtension: "mp4") }

    func makeUIView(context: Context) -> PlayerView {
        PlayerUIView(frame: .zero , url  : myUrl)
    }

    // ### This one weird trick makes OS call updateUIView when view is disappearing.
    class DummyClass { } ; let x = DummyClass()

    func updateUIView(_ v: PlayerView, context: UIViewRepresentableContext<PlayerView>) {
        print("> updateUIView()")
        print("  router.isPlayingAV = \(router.isPlayingAV)")
        // print("  isPlaying = \(isPlaying)") // %%%

        // This does work. But *only* with the Dummy code ### included.
        // See also +++ comment in HomeView
        if router.isPlayingAV  { v.player?.pause() }
        else                   { v.player?.play() }

        // This logic looks reversed, but is correct.
        // If it's the other way around, vid never plays. Try it!
        //   if isPlaying { v?.player?.play()   }   // %%%
        //   else         { v?.player?.pause()  }   // %%%

        print("< updateUIView()")
    }
}

和 wrappED UIView:

class PlayerUIView: UIView {
    private let playerLayer = AVPlayerLayer()
    var player: AVPlayer?

    init(frame: CGRect, url: URL?) {
        super.init(frame: frame)
        guard let u = url else { return }

        self.player = AVPlayer(url: u)
        self.playerLayer.player = player
        self.layer.addSublayer(playerLayer)
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        playerLayer.frame = bounds
    }

    required init?(coder: NSCoder) { fatalError("not implemented") }
}

当然还有视图路由器，基于 Blckbirds 示例

class ViewRouter : ObservableObject {
    let objectWillChange = PassthroughSubject<ViewRouter, Never>()

    enum Page { case home, movie }

    var page = Page.home { didSet { objectWillChange.send(self) } }

    // Claim: App will never play more than one vid at a time.
    var isPlayingAV = false  // No didSet necessary.
}

控制台日志

控制台日志 1（根据需要播放停止）

> updateUIView()                // First call
  router.isPlayingAV = false    // Vid is not playing => play it.
< updateUIView()
> onAppear()
< onAppear()
> updateUIView()                // Second call
  router.isPlayingAV = true     // Vid is playing => pause it.
< updateUIView()
> onDisappear()                 // After the fact, we clear
< onDisappear()                 // the isPlayingAV flag.

控制台日志 2（禁用怪异技巧；继续播放）

> updateUIView()                // First call
  router.isPlayingAV = false
< updateUIView()
> onAppear()
< onAppear()
                                // No second call.
> onDisappear()
< onDisappear()

控制台日志 3（尝试使用状态和绑定；播放继续）

> updateUIView()
  isPlaying = false
< updateUIView()
> onAppear()
< onAppear()
> updateUIView()
  isPlaying = true
< updateUIView()
> updateUIView()
  isPlaying = true
< updateUIView()
> onDisappear()
< onDisappear()

Answer 1

嗯...在

}.onDisappear {
    print("> onDisappear()")
    self.router.isPlayingAV = false
    print("< onDisappear()")
}

这在删除视图后称为（类似于didRemoveFromSuperview，而不是will...），所以我什么都看不到bad/wrong/unexpected 中的子视图（甚至它本身）没有更新（在这种情况下 updateUIView）...如果是这样我会感到惊讶（为什么更新视图, 哪个不在视图层次结构中？！）。

所以这个

class DummyClass { } ; let x = DummyClass()

是一些野生错误，或...错误。算了，别再用这种东西发产品了。

好的，现在有人会问，这个怎么办？我在这里看到的主要问题是由设计引起的，特别是 PlayerUIView 中模型和视图的紧密耦合，因此无法管理工作流。 AVPlayer 这里不是视图的一部分 - 它是模型并根据其状态 AVPlayerLayer 绘制内容。因此，解决方案是将这些实体分开并分别管理：一个视图一个视图，一个模型一个模型。

这是一个修改和简化方法的演示，它的行为符合预期（w/o 奇怪的东西和 w/o Group/ZStack 限制），并且可以很容易地扩展或改进它（在 model/viewmodel 层）

测试 Xcode 11.2 / iOS 13.2

完整的模块代码（可以从模板复制粘贴到项目的ContentView.swift中）

import SwiftUI import Combine import AVKit struct MovieView: View { @EnvironmentObject var router: ViewRouter // just for demo, but can be interchangable/modifiable let playerModel = PlayerViewModel(url: Bundle.main.url(forResource: "myVid", withExtension: "mp4")!) var body: some View { VStack() { PlayerView(viewModel: playerModel) Button(action: { self.router.page = .home }) { Text("Go back Home") } }.onAppear { self.playerModel.player?.play() // << changes state of player, ie model }.onDisappear { self.playerModel.player?.pause() // << changes state of player, ie model } } } class PlayerViewModel: ObservableObject { @Published var player: AVPlayer? // can be changable depending on modified URL, etc. init(url: URL) { self.player = AVPlayer(url: url) } } struct PlayerView: UIViewRepresentable { // just thing wrapper, as intended var viewModel: PlayerViewModel func makeUIView(context: Context) -> PlayerUIView { PlayerUIView(frame: .zero , player: viewModel.player) // if needed viewModel can be passed completely } func updateUIView(_ v: PlayerUIView, context: UIViewRepresentableContext<PlayerView>) { } } class ViewRouter : ObservableObject { enum Page { case home, movie } @Published var page = Page.home // used native publisher } class PlayerUIView: UIView { private let playerLayer = AVPlayerLayer() var player: AVPlayer? init(frame: CGRect, player: AVPlayer?) { // player is a model so inject it here super.init(frame: frame) self.player = player self.playerLayer.player = player self.layer.addSublayer(playerLayer) } override func layoutSubviews() { super.layoutSubviews() playerLayer.frame = bounds } required init?(coder: NSCoder) { fatalError("not implemented") } } struct ContentView: View { @EnvironmentObject var router: ViewRouter var body: some View { Group { if router.page == .home { Button(action: { self.router.page = .movie }) { Text("Go to Movie") } } else if router.page == .movie { MovieView() } } } }

backup

让 AVPlayer 的 SwiftUI 包装器在视图消失时暂停

Getting SwiftUI wrapper of AVPlayer to pause when view disappears

data-binding

wrapper

avplayer

swiftui