不能在属性初始化程序中使用实例成员“videoName”；属性初始化程序在 'self' 可用之前运行答案

【问题标题】：Cannot use instance member 'videoName' within property initializer; property initializers run before 'self' is available不能在属性初始化程序中使用实例成员“videoName”；属性初始化程序在 'self' 可用之前运行
【发布时间】：2021-10-02 14:03:27
【问题描述】：

我对 SwiftUI 很陌生，当我尝试使用 Model 中的 videoName 显示视频时遇到了这个问题。在 player = AVPlayer(...)(line 4) 中，我不想通过字符串“squats”查找资源，而是想使用 Model 中的 videoName。如果我替换它们，我会收到错误

不能在属性初始化器中使用实例成员“videoName”；属性初始化器在“self”可用之前运行

谁能帮帮我？

这是我的代码：

struct ExercisingSessionView: View {
    
    let exerciseName: String
    let videoName: String
    
    @State var player = AVPlayer(url: URL(fileURLWithPath: Bundle.main.path(forResource: "squats", ofType: "mov")!))
    @State var isplaying = false
    @State var showcontrols = false
    
    var body: some View {
        
        CustomVideoPlayer(player: $player)
            .frame(width: 390, height: 219)
            .onTapGesture {
                self.showcontrols = true
                
            }
    }
    
    struct CustomVideoPlayer : UIViewControllerRepresentable {
        
        @Binding var player: AVPlayer
        
        func makeUIViewController(context: UIViewControllerRepresentableContext<CustomVideoPlayer>) -> AVPlayerViewController {
            
            let controller = AVPlayerViewController()
            controller.player = player
            controller.showsPlaybackControls = false
            return controller
        }
        
        func updateUIViewController(_ uiViewController: AVPlayerViewController, context: UIViewControllerRepresentableContext<CustomVideoPlayer>) {
            
        }
    }
}

【问题讨论】：

标签： swiftui model video-player

【解决方案1】：

选项1：

为您的 View 创建一个初始化程序，用于创建您的 @State 初始值：

struct ExercisingSessionView: View {
    
    let exerciseName: String
    let videoName: String
    
    @State var player : AVPlayer
    @State var isplaying = false
    @State var showcontrols = false
    
    init(exerciseName: String, videoName: String) {
        self.exerciseName = exerciseName
        self.videoName = videoName
        self._player = State(initialValue: AVPlayer(url: URL(fileURLWithPath: Bundle.main.path(forResource: videoName, ofType: "mov")!)))
    }
    
    var body: some View {
        CustomVideoPlayer(player: $player)
            .frame(width: 390, height: 219)
            .onTapGesture {
                self.showcontrols = true
            }
    }
}

这样做的缺点是如果ExercisingSessionView 经常被初始化（即使它实际上并没有被重新渲染到视图层次结构中），那么你在init 内部做了大量的工作，这通常是一个非常糟糕的事情性能理念。

选项2：

将player声明为可选，并在onAppear中加载初始值：



struct ExercisingSessionView: View {
    
    let exerciseName: String
    let videoName: String
    
    @State var player : AVPlayer?
    @State var isplaying = false
    @State var showcontrols = false
    
    var body: some View {
        Group {
            if let player = player {
                CustomVideoPlayer(player: player)
                    .frame(width: 390, height: 219)
                    .onTapGesture {
                        self.showcontrols = true
                    }
            }
        }.onAppear {
            player = AVPlayer(url: URL(fileURLWithPath: Bundle.main.path(forResource: videoName, ofType: "mov")!))
        }
    }
}

struct CustomVideoPlayer : UIViewControllerRepresentable {
    var player: AVPlayer
    
    func makeUIViewController(context: UIViewControllerRepresentableContext<CustomVideoPlayer>) -> AVPlayerViewController {
        
        let controller = AVPlayerViewController()
        controller.player = player
        controller.showsPlaybackControls = false
        return controller
    }
    
    func updateUIViewController(_ uiViewController: AVPlayerViewController, context: UIViewControllerRepresentableContext<CustomVideoPlayer>) {
        
    }
}

这避免了选项 1 中的问题，因为 onAppear 只会被调用一次。

请注意，在这里，我在 CustomVideoPlayer 中创建了 player 一个常规的、非绑定属性——因为 AVPlayer 是一个类，通过引用传递，没有理由与它一起使用 @Binding .

【讨论】：

【解决方案2】：

您可以将您的名字传递给您的自定义视图。

struct ExercisingSessionView: View {
    
    let exerciseName: String
    let videoName: String
    
    @State var isplaying = false
    @State var showcontrols = false
    
    var body: some View {
        
        CustomVideoPlayer(player: videoName)
            .frame(width: 390, height: 219)
            .onTapGesture {
                self.showcontrols = true
                
            }
    }
    
    struct CustomVideoPlayer : UIViewControllerRepresentable {
        
        let videoName: String
        
        func makeUIViewController(context: UIViewControllerRepresentableContext<CustomVideoPlayer>) -> AVPlayerViewController {
            
            let controller = AVPlayerViewController()
            controller.player = AVPlayer(url: URL(fileURLWithPath: Bundle.main.path(forResource: videoName, ofType: "mov")!))
            controller.showsPlaybackControls = false
            return controller
        }
}

【讨论】：

【解决方案3】：

当您将 squats 替换为 videoName 时，我假设此行发生了错误：

@State var player = AVPlayer(url: URL(fileURLWithPath: Bundle.main.path(forResource: "squats", ofType: "mov")!))

您收到错误的原因是因为在您调用这行代码时未定义videoName。

要解决此问题，您可以在您定义的自定义 init 方法中设置您的属性。像这样：

    let videoName: String
    @State var player: AVPlayer
    
    init(exerciseName: String, videoName: String) {
        self.exerciseName = exerciseName
        self.videoName = videoName
        self.player = AVPlayer(url: URL(fileURLWithPath: Bundle.main.path(forResource: videoName, ofType: "mov")!))
    }

记住，你必须添加

【讨论】：