调用中缺少参数 'message' 的参数

Question

我带着另一个问题回来了。我遵循了这个指南：https://medium.com/@fs.dolphin/passing-data-between-views-in-swiftui-793817bba7b1

一切正常，但 SecondView_Previews 抛出错误 Missing argument for parameter 'message' in call。这是我的 ContentView 和 SecondView

// ContentView
import SwiftUI

struct ContentView: View {
    @State private var showSecondView = false
    @State var message = "Hello from ContentView"
    
    var body: some View {
        VStack {
            Button(action: {
                self.showSecondView.toggle()
            }){
               Text("Go to Second View")
            }.sheet(isPresented: $showSecondView){
                SecondView(message: self.message)
        }
            Button(action: {
                self.message = "hi"
            }) {
                Text("click me")
            }
        }
    }
}
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

import SwiftUI

struct SecondView: View {
    @State var message: String
    
    var body: some View {
        Text("\(message)")
    }
}
 struct SecondView_Previews: PreviewProvider {
    static var previews: some View {
        SecondView() // Error here: Missing argument for parameter 'message' in call.
    }
 }

它尝试将其更改为 SecondView(message: String)，错误更改为“无法将类型 'String.Type' 的值转换为预期的参数类型 'String'”

谁能解释一下我做错了什么，或者如何正确设置预览。没有预览时一切正常。提前致谢！

Answer 1

struct ContentView: View {
    @State var message: String //Define type here 
        var body: some View {
            Text("\(message)")
        }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView(message: "Some text") //Passing value here 
    }
}

调用中缺少参数 'message' 的参数

Missing argument for parameter 'message' in call

xcode

swift

swiftui

xcode12

xcode-previews