How-To: Display a Message Dialog

This topic walks through using Navigation to display a prompt using a MessageDialog. This can also be used for simple user interactions, such as a confirmation dialog, where the user is prompted with an Ok/Cancel, or Yes/No, question.

Step-by-steps

Important

This guide assumes you used the template wizard or dotnet new unoapp to create your solution. If not, it is recommended that you follow the instructions for creating an application from the template.

1. Show an ad-hoc MessageDialog

• Update the existing Button on MainPage.xaml

  <Button Content="Show Simple Message Dialog"
          Click="{x:Bind ViewModel.ShowSimpleDialog}"
          Grid.Row="1"
          HorizontalAlignment="Center"
          VerticalAlignment="Center" />
  

• Add ShowSimpleDialog method to MainViewModel

  public async Task ShowSimpleDialog()
  {
      _ = _navigator.ShowMessageDialogAsync(this, title: "This is Uno", content: "Hello Uno.Extensions!");
  }
  

  Run the application to see a MessageDialog displayed when you click the Button.

  

2. Accessing the MessageDialog response

• Change code in the ShowSimpleDialog method to await response

  public async Task ShowSimpleDialog()
  {
      var result = await _navigator.ShowMessageDialogAsync<string>(this, title: "This is Uno", content: "Hello Uno.Extensions!");
  }
  

• Modify the ShowMessageDialogAsync method call to specify multiple buttons.

  public async Task ShowSimpleDialog()
  {
   var result = await _navigator.ShowMessageDialogAsync<string>(this,
    title: "This is Uno",
    content: "Hello Uno.Extensions!",
    buttons: new[]
          {
     new DialogAction("Ok"),
     new DialogAction("Cancel")
          });
  }
  

  The result variable will be set to the label of the selected button.

  

3. Using predefined MessageDialog

If you want to use the same MessageDialog in different places in your application you can define a MessageDialogViewMap and then reference it by the route you assign to it.

• Create a MessageDialogViewMap instance and register it with both views and routes in App.xaml.host.cs

  private static void RegisterRoutes(IViewRegistry views, IRouteRegistry routes)
  {
      var messageDialog = new MessageDialogViewMap(
          title: "This is Uno",
          Content: "Hello Uno.Extensions",
          Buttons: new[]
          {
              new DialogAction(Label:"Yes"),
              new DialogAction(Label:"No")
          }
      );
  
  
   views.Register(
    new ViewMap<ShellControl,ShellViewModel>(),
    new ViewMap<MainPage, MainViewModel>(),
    new ViewMap<SecondPage, SecondViewModel>(),
          messageDialog
    );
  
   routes
    .Register(
     new RouteMap("", View: views.FindByViewModel<ShellViewModel>() ,
                  Nested: new RouteMap[]
                  {
                   new RouteMap("Main", View: views.FindByViewModel<MainViewModel>()),
                   new RouteMap("Second", View: views.FindByViewModel<SecondViewModel>()),
                      new RouteMap("MyMessage", View: messageDialog)
                  }));
  }
  

• In MainViewModel change the ShowMessageDialogAsync method to specify the route argument, which should be the route specified in the the RouteMap

  var result = await _navigator.ShowMessageDialogAsync<string>(this, route: "MyMessage");
  

4. Localize the MessageDialog

• For a localized MessageDialog create a LocalizableMessageDialogViewMap instance and register it with both views and routes (as per previous step). Note that each of the properties in the LocalizableMessageDialogViewMap that were a simple string in the MessageDialogViewMap, are now call-back methods that provide an IStringLocalizer instance.

  var localizedMessageDialog = new LocalizableMessageDialogViewMap(
      Content: localizer => localizer?["MyDialog_Content"]??string.Empty,
   Buttons: new[]
      {
    new LocalizableDialogAction( LabelProvider:localizer=>localizer?["Dialog_Ok"]??string.Empty),
          new LocalizableDialogAction( LabelProvider:localizer=>localizer?["Dialog_Cancel"]??string.Empty)
      }
  );
  

• Add resources for MyDialog_Content, Dialog_Ok and Dialog_Cancel to Resources.resw

• Make sure the UseLocalization extension method is called in the BuildAppHost method in App.xaml.host.cs

  private static IHost BuildAppHost()
  { 
   return UnoHost
     .CreateDefaultBuilder()
     // ... omitted for brevity
     .UseLocalization()
     .Build(enableUnoLogging: true);
  
  }
  

• In MainViewModel change the ShowMessageDialogAsync method to use the MyLocalizedMessage route (this route should match the name of the route that was added to the routes earlier).

  var result = await _navigator.ShowMessageDialogAsync<string>(this, route: "MyLocalizedMessage");