Swift UI 将绑定传递给另一个视图以通过 init 发出警报

Question

我可以在没有初始化的情况下将绑定传递给另一个视图，并且它工作得很好。但是，如果我尝试使用具有 init 的视图，我将无法克服错误。

struct ContentView: View {
    // MARK: - PROPERTIES
    @State private var showAlert = false
    @State private var alert: Alert? = nil
    @State private var alertTitle = ""
    @State private var alertMessage = ""
    
    // MARK: - BODY
    var body: some View {
        VStack {
            Button(action: {
                alertTitle = "Alert 1"
                alertMessage = "From Main View"
                showAlert.toggle()
            }, label: {
                Text("Show Parent Alert")
            })
            
            // MARK: - TESTVIEW1
            TestView1(showAlert: $showAlert, alert: $alert, alertTitle: $alertTitle, alertMessage: $alertMessage)
        } // END:VSTACK
        .alert(isPresented: $showAlert, content: {
            Alert(title: Text(alertTitle), message: Text(alertMessage), dismissButton: .default(Text("Close")))
        })
    }
}

struct TestView1: View {
    // MARK: - PROPERTIES
    @Binding var showAlert: Bool
    @Binding var alert: Alert?
    @Binding var alertTitle: String
    @Binding var alertMessage: String
    
    // MARK: - BODY
    var body: some View {
        VStack {
            Button(action: {
                alertTitle = "Alert 2"
                alertMessage = "From TestView1"
                showAlert.toggle()
            }, label: {
                Text("Show View-1 Alert")
            })
            
            TestView2(showAlert: $showAlert, alert: $alert, alertTitle: $alertTitle, alertMessage: $alertMessage)
        } // END:VSTACK
    }
}

这很好，但如果我有一个 init，我会收到错误“无法将 'Alert?.Type' 类型的值分配给类型 'Alert'”

struct TestView1: View {
    // MARK: - PROPERTIES
    @Binding var showAlert: Bool
    @Binding var alert: Alert?
    @Binding var alertTitle: String
    @Binding var alertMessage: String
    
    init(showAlert: Binding<Bool>, alert: Binding<Alert>, alertTitle: Binding<String>, alertMessage: Binding<String>) {
        self.showAlert = false
        self.alert = Alert?
        self.alertTitle = ""
        self.alertMessage = ""
    }

Answer 1

如果您有一个接受 Binding 的 init，则需要将 Binding（而不是值）分配给 @Binding 属性。您可以使用 _ 前缀来做到这一点。

init(showAlert: Binding<Bool>, 
     alert: Binding<Alert>, 
     alertTitle: Binding<String>, 
     alertMessage: Binding<String>) {

   self._showAlert = showAlert
   self._alert = alert
   self._alertTitle = alertTitle
   self._alertMessage = alertMessage
}