In SwiftUI, is it possible to use a modifier only for a certain os target?

问题

Good day! In SwiftUI, is it possible to use a modifier only for a certain os target? In the following code I would like to use the modifier .listStyle(SidebarListStyle()) only for the MacOS target because it does not exist for the iOS target. Thanks for you help.

import SwiftUI

struct ContentView: View {

  @State var selection: Int?

  var body: some View {

    HStack() {
      NavigationView {
        List () {
          NavigationLink(destination: FirstView(), tag: 0, selection: self.$selection) {
            Text("Click Me To Display The First View")
          } // End Navigation Link

          NavigationLink(destination: SecondView(), tag: 1, selection: self.$selection) {
            Text("Click Me To Display The Second View")
          } // End Navigation Link

        } // End list
        .frame(minWidth: 350, maxWidth: 350)
        .onAppear {
            self.selection = 0
        }

      } // End NavigationView
        .listStyle(SidebarListStyle())
        .frame(maxWidth: .infinity, maxHeight: .infinity)

    } // End HStack
  } // End some View
} // End ContentView

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

回答1:

your better off doing this:

 import SwiftUI

 struct ContentView: View {

@State var selection: Int?

var body: some View {
    #if targetEnvironment(macCatalyst)
    return theList.listStyle(SidebarListStyle())
    #else
    return theList.navigationViewStyle(DefaultNavigationViewStyle())
    #endif
}

 var theList: some View {
 HStack() {
   NavigationView {
     List () {
       NavigationLink(destination: FirstView(), tag: 0, selection: self.$selection) {
         Text("Click Me To Display The First View")
       } // End Navigation Link

       NavigationLink(destination: SecondView(), tag: 1, selection: self.$selection) {
         Text("Click Me To Display The Second View")
       } // End Navigation Link

     } // End list
     .frame(minWidth: 350, maxWidth: 350)
     .onAppear {
         self.selection = 0
     }

   } // End NavigationView
     .frame(maxWidth: .infinity, maxHeight: .infinity)

 } // End HStack
 } // End some View
 } // End ContentView
 }

回答2:

Thanks DoesData for giving me the direction.

The solution was to use #is os(macOS) around the entire code and not only around the modifier itself.

import SwiftUI

struct ContentView: View {

  @State var selection: Int?

  var body: some View {

    #if os(macOS)
    HStack() {
      NavigationView {
        List () {
          NavigationLink(destination: FirstView(), tag: 0, selection: self.$selection) {
            Text("Click Me To Display The First View")
          } // End Navigation Link

          NavigationLink(destination: SecondView(), tag: 1, selection: self.$selection) {
            Text("Click Me To Display The Second View")
          } // End Navigation Link

        } // End list
          .frame(minWidth: 350, maxWidth: 350)
          .onAppear {
            self.selection = 0
        }

      } // End NavigationView
        .listStyle(SidebarListStyle())
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    } // End HStack

    #elseif os(iOS)
    HStack() {
      NavigationView {
        List () {
          NavigationLink(destination: FirstView(), tag: 0, selection: self.$selection) {
            Text("Click Me To Display The First View")
          } // End Navigation Link

          NavigationLink(destination: SecondView(), tag: 1, selection: self.$selection) {
            Text("Click Me To Display The Second View")
          } // End Navigation Link

        } // End list
          .frame(minWidth: 350, maxWidth: 350)
          .onAppear {
            self.selection = 0
        }

      } // End NavigationView
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    } // End HStack
    #endif

  } // End some View
} // End ContentView

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

回答3:

WorkingDog, I try your elegante code with a very simple code to change the text color depending on the Target... but the text stays blue on both target and does not go red on MacOS!

import SwiftUI

struct ContentView: View {

    var body: some View {

      #if os(macOS)
      return monText.foregroundColor(Color.red)
      #elseif os(iOS)
       return monText.foregroundColor(Color.blue)
      #endif
      }

  var monText: some View {
    Text("Hello, World!")
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

来源：https://stackoverflow.com/questions/61386877/in-swiftui-is-it-possible-to-use-a-modifier-only-for-a-certain-os-target