SwiftUI Xcode 11 beta 5/6:没有更多上下文的表达式类型不明确 [英] SwiftUI Xcode 11 beta 5 / 6: Type of expression is ambiguous without more context

问题描述

从 beta 5 开始，我的项目将不再编译.对于该按钮的文本，错误是 没有更多上下文的表达式类型不明确".我认为它可能会在 beta 6 中修复，但事实并非如此.macOS 也更新到 Catalina beta 7.

Since beta 5 my Project won't compile anymore. The error is "Type of expression is ambiguous without more context"for that Button's Text. I thought it would be fixed with beta 6 maybe, but it wasn't. macOS is also updated to Catalina beta 7.

 class ClPassport : ObservableObject , Identifiable {


    @Published var mrz : String =  "" //{ didSet { update() } } 
    var isValid : Bool {
        return true
    }

    func update() {
        objectWillChange.send(())
    }

    func getMRZKey() -> String {
     return ""
    }
}


struct ContentView : View {

    @ObservedObject var passportDetails = ClPassport()
      var body: some View {

         ZStack{
           VStack(alignment: .leading){
             HStack{
                  Spacer()
                  Button(action: {
                      self.scanPassport( mrzKey: self.passportDetails.getMRZKey() )
                    }) {
                        Text("Read Chip") // <-  "Type of expression is ambiguous without more context"
                            .font(.largeTitle)
                        .foregroundColor(passportDetails.isValid ? .primary : Color.secondary.opacity(0.25))
                            .padding()
                        }.padding()
                        .background(Color.white.opacity(passportDetails.isValid ? 1 : 0.5))
                        .cornerRadius(15)
                        .padding()
                        .disabled( !passportDetails.isValid )
                   Spacer()
              }
            TextField($passportDetails.mrz, placeholder: Text("MRZ"))
            }
          }
        }

 func scanPassport( mrzKey: String ) {
   //do stuff with mrzKey
 }
}

推荐答案

在您更新答案后，我发现需要进行一些更改:

After your update in your answer, I see some changes needed:

• 使用ObservableObject(无需使用Combine.ObservableObject)
• 缺少功能scanPassport，我添加了一个假的.
• willChange 不再存在，现在是 objectWillChange.它是为您自动合成的.

• Use ObservableObject (no need to use Combine.ObservableObject)
• Missing function scanPassport, I added a bogus one.
• willChange no longer exists, it is now objectWillChange. And it is autosynthesize for you.

import SwiftUI

class ClPassport : ObservableObject , Identifiable {


    @Published var mrz : String =  "" //{ didSet { update() } }
    var isValid : Bool {
        return true
    }

    func update() {
        objectWillChange.send()
    }

    func getMRZKey() -> String {
     return ""
    }
}


struct ContentView : View {

    @ObservedObject var passportDetails = ClPassport()
      var body: some View {

         ZStack{
           VStack(alignment: .leading){
             HStack{
                  Spacer()
                  Button(action: {
                      self.scanPassport( mrzKey: self.passportDetails.getMRZKey() )
                    }) {
                        Text("Read Chip")
                            .font(.largeTitle)
                        .foregroundColor(passportDetails.isValid ? .primary : Color.secondary.opacity(0.25))
                            .padding()
                        }.padding()
                        .background(Color.white.opacity(passportDetails.isValid ? 1 : 0.5))
                        .cornerRadius(15)
                        .padding()
                        .disabled( !passportDetails.isValid )
                   Spacer()
              }
            TextField("MRZ", text: $passportDetails.mrz)
            }
          }
        }

 func scanPassport( mrzKey: String ) {
   //do stuff with mrzKey
 }
}

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