ios - 变量不在范围内，即使它出现在 Swift 中同一范围内的其他地方

Question

我正在 Swift 中测试 Prafulla Singh 的字幕文本，我目前遇到一个错误，即变量声称不在范围内，即使在其他地方看起来是相同的范围内，它也被调用和工作。我附上了整个代码，因为我觉得好像有必要查看变量范围。

struct test_marquee: App {
    var body: some Scene {
        WindowGroup {
            struct Marque: View {
                let text: String
                @State private var moveView = false
                @State private var stopAnimation = false
                // ####
                @State private var textFrame: CGRect = CGRect() //DECLARATION FOR ERROR VARIABLE
                public init(text: String) {
                    self.text = text
                }
                var body: some View {
                    GeometryReader { proxy in
                        ScrollView(.horizontal, showsIndicators: false, content: {
                            Text(text)
                                .lineLimit(1)
                                .background(GeometryGetter(rect: $textFrame)).offset(moveView ? CGSize(width: -1 * textFrame.width, height: 0) : CGSize(width: proxy.size.width, height: 0))
                                .onAppear() {
                                    self.stopAnimation = false
                                    animateView()
                                    moveViewOnAnimationEnd()///scrollViewProxy.scrollTo("Identifier") /// does not animate
                                }.onDisappear() {
                                    self.stopAnimation = true
                                }
                        }).mask(LinearGradient(gradient: Gradient(colors: [Color.clear, Color.black, Color.black, Color.clear]), startPoint: .leading, endPoint: .trailing))
                        .padding([.top, .bottom], 100)
                    }
                }
                private func animateView() {
                    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1, execute: { //after 0.5 sec
                        withAnimation(Animation.linear(duration: Double(textFrame.width) * 0.01)) {
                            // ######
                            //textFrame IS CALLED HERE WITH NO ISSUES
                            moveView = true
                        }//no on completion so need to add another time bound method to restart animation from start
                    })
                }
                private func moveViewOnAnimationEnd() {
                    // ######
                    let timeToAnimate = (Double(textFrame.width) * 0.01) + 0.2
                    // ERROR OCCURS ON THIS LINE ON THE textFrame rect
                    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + timeToAnimate, execute: { //after 0.5 sec
                        moveView = false
                        if stopAnimation == false {
                            animateView()
                            moveViewOnAnimationEnd()
                        }
                    })
                }
                
                
                struct GeometryGetter: View {
                    @Binding var rect: CGRect
                    
                    var body: some View {
                        GeometryReader { (proxy) -> Path in
                            DispatchQueue.main.async {
                                self.rect = proxy.frame(in: .global)
                            }
                            return Path()
                        }
                    }
                }
                
                struct Marque_Previews: PreviewProvider {
                    
                    static var previews: some View {
                        Marque(text: "If you don't provide your own init with an explicit public modifier the generated constructor will be marked internal")
                    }
                }
            }
        }
    }
}

Answer 1

这可能是 ViewBuilder(或 _functionBuilder)的错误，这就是 WindowGroup正在使用它的内容...但是你为什么要声明 Marque类型 里面 WindowGroup { }内容关闭？
正常声明，在 WindowGroup 之外的闭包，但在外部结构内部，如果您愿意:

struct TestMarquee: App {
   struct Marque: View {
      // the rest of your code...
   }

   var body: some Scene {
      WindowGroup {
         Marque(text: "whatever") // instantiate here; don't declare
      }
   }
}

{ }的 WindowGroup表示尾随闭包语法。但这是 @ViewBuilder 使用的“特殊”类型的闭包。提取( read here for more info) View s 来自闭包内的每个代码块。这些不是 { }用于定义类似结构或函数的范围。