如何预览依赖于PresentationMode的SwiftUI按钮？

Question

如何预览依赖于PresentationMode的SwiftUI按钮？

4

如何预览需要PresentationMode才能构建的此按钮？在包含该按钮的主视图中，通过声明一个环境PresentationMode对象来创建它，该按钮可以正常工作：

@Environment(\.presentationMode) var presentationMode:Binding<PresentationMode>

struct BackButton: View {
  @Binding var presentationMode: PresentationMode
  var color: Color
  var body: some View {
    Button(action: {
      self.$presentationMode.wrappedValue.dismiss()
    }, label: { Image(systemName: "chevron.left")
      .scaleEffect(1.3)
      .foregroundColor(color)
      .offset(x: -17)
      .frame(width: 43, height: 43)
    }
    )
  }
}

struct BackButton_Previews: PreviewProvider {
    static var previews: some View {
        let pres = PresentationMode()
      return BackButton(presentationMode: pres, color: .black) // Compiler Error: PresentationMode cannot be constructed because it has no accessible initializers
    }
}

- onthemoon

1个回答

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- davidev · Accepted Answer

我认为PresentationMode应该被声明为环境变量。所以像这样声明它。

@Environment(\.presentationMode) var presentationMode

然后在操作中进行更改，因为它不再是绑定。

Button(action: {
    self.presentationMode.wrappedValue.dismiss()

编辑：

这里有一个可工作的示例/预览，展示了BackButton View和如何使用PresentationMode。

struct MainView: View {
    var body: some View {
    
        NavigationView
        {
            VStack()
            {
                Text("Hello World")
                
                NavigationLink("Go to Detail View", destination: BackButton(color: .black))
        
            }.navigationBarTitle(Text("Main View"))
        }
    }
}


struct BackButton : View
{
    //Environment variable here
    @Environment(\.presentationMode) var presentationMode
    
    var color: Color
    
    var body: some View
    {
        Button(action: {
            //Dismiss the View
            self.presentationMode.wrappedValue.dismiss()
        }, label: { Image(systemName: "chevron.left")
          .scaleEffect(1.3)
          .foregroundColor(color)
          .offset(x: -17)
          .frame(width: 43, height: 43)
        })
    }
}

struct BackButton_Previews: PreviewProvider {
    static var previews: some View {
        //Preview here is working, no need to pass environment variable
        //Going back from this view in Preview won't work
        BackButton(color: .black)
    }
}