Introduction

What is Navigation?

Navigation needs to encompass a range of UI concepts:

• Navigation between pages in a Frame (forward and backwards)
• Switching between menu items in a NavigationView, or between tab items in a TabBar
• Loading content into a ContentControl
• Loading and toggling visibility of child elements in a Grid
• Displaying a Popup or Flyout
• Prompt a ContentDialog or MessageDialog

What triggers Navigation?

Navigation can be triggered for a number of reasons:

• Change view
  Either based on the type of View or the type of ViewModel to show
• Display data
  The view to show is based on the type of data to display (eg display ProductX)
• Prompt, or request, for data
  The view to show is based on the type of data being requested (eg Country picker)
  Prompt the user using a flyout or content dialog to get a response

Architecture Objectives

Navigation needs to be accessible from anywhere

• View (Code behind)
  i.e. in context of a page/usercontrol
• View (XAML)
  i.e. using attached properties
• ViewModel (Presentation)
  i.e. in a context that doesn't have access to the UI layer

Navigation needs to make use of available data

• Uri
  Used to share links to the app (eg deeplink)
• DTO
  If an instance of an entity is already in memory, navigation should support passing the existing entity between views
• ViewModel
  The type of viewmodel (associated with the view) to navigate to
• View
  The type of view to navigate to

Common Scenarios

1. Navigating between pages (code behind)

• Navigate forward to a new page by calling NavigateRouteAsync with the route to navigate to

  XAML

  <Page x:Class="Playground.Views.HomePage">
      <Button Click="{x:Bind GoToSecondPageClick}"
              Content="Go to Second Page - Code behind" />
  </Page>
  

  C#

  public sealed partial class HomePage : Page
  {
      public async void GoToSecondPageClick()
      {
          var nav = this.Navigator();
          await nav.NavigateRouteAsync(this, "Second");
      }
  }
  

• Navigate back to the previous page by calling NavigateBackAsync

  XAML

  <Page x:Class="Playground.Views.SecondPage">
      <Button Click="{x:Bind GoBackClick}"
              Content="Go Back" />
  </Page>
  

  C#

  public sealed partial class SecondPage : Page
  {
      public async void GoBackClick()
      {
          var nav = this.Navigator();
          await nav.NavigateBackAsync(this);
      }
  }
  

2. Navigating between view models

• Navigate forward to a new page by calling NavigateViewModelAsync with the route to navigate to

  XAML

  <Page x:Class="Playground.Views.HomePage">
      <Button Click="{x:Bind ViewModel.GoToSecondPageClick}"
              Content="Go to Second Page - View Model" />
  </Page>
  

  C#

  public sealed partial class HomeViewModel
  {
      private readonly INavigator _navigator;
      public HomeViewModel(INavigator navigator)
      {
          _navigator = navigator;
      }
  
      public async void GoToSecondPageClick()
      {
          await _navigator.NavigateViewModelAsync<SecondViewModel>(this);
      }
  }
  

• Navigate back to the previous page by calling NavigateBackAsync

  XAML

  <Page x:Class="Playground.Views.SecondPage">
      <Button Click="{x:Bind ViewModel.GoBackClick}"
              Content="Go Back" />
  </Page>
  

  C#

  public sealed partial class SecondViewModel
  {
      private readonly INavigator _navigator;
      public SecondViewModel(INavigator navigator)
      {
          _navigator = navigator;
      }
  
      public async void GoBackClick()
      {
          await _navigator.NavigateBackAsync(this);
      }
  }
  

3. Navigating between pages (XAML)

• Navigate forward to new page by specifying the route in the Navigation.Request attached property

  XAML

  <Page x:Class="Playground.Views.HomePage">
      <Button uen:Navigation.Request="Second"
              Content="Go to Second Page - XAML" />
  </Page>
  

• Navigate to previous page by specifying the back qualifier in the Navigation.Request attached property
  XAML

  <Page x:Class="Playground.Views.SecondPage">
      <Button uen:Navigation.Request="-"
              Content="Go Back" />
  </Page>
  

4. Navigating between pages (XAML)

• Navigate forward to new page and clearing back-stack by specifying the route in the Navigation.Request attached property with the clear back-stack qualifier ("-/")
  XAML

  <Page x:Class="Playground.Views.HomePage">
      <Button uen:Navigation.Request="-/Second"
              Content="Go to Second Page - XAML" />
  </Page>
  

5. Prompt user - Message Dialog

• Prompt the user with a message using the ShowMessageDialogAsync method.
  C#

  public sealed partial class HomePage : Page
  {
      public async void PromptWithMessageDialogClick()
      {
          var nav = this.Navigator();
          var messageResult = await nav.ShowMessageDialogAsync(this,"Warning about something","Alert");
      }
  }
  

6. Switching items in NavigationView

• Define selectable navigation view items by setting the Region.Name. When an item is selected, the child element of the Grid with the same Region.Name will be set to Visible (and the others set back to Collapsed)
  XAML

  <Page x:Class="Playground.Views.NavigationViewPage">
  
      <Grid>
          <muxc:NavigationView uen:Region.Attached="true">
              <muxc:NavigationView.MenuItems>
                  <muxc:NavigationViewItem Content="Products"
                                           uen:Region.Name="Products" />
                  <muxc:NavigationViewItem Content="Deals"
                                           uen:Region.Name="Deals" />
                  <muxc:NavigationViewItem Content="Profile"
                                           uen:Region.Name="Profile" />
              </muxc:NavigationView.MenuItems>
              <Grid uen:Region.Attached="True">
                  <StackPanel uen:Region.Name="Products"
                              Visibility="Collapsed">
                      <TextBlock Text="Products" />
                  </StackPanel>
                  <StackPanel uen:Region.Name="Deals"
                              Visibility="Collapsed">
                      <TextBlock Text="Deals" />
                  </StackPanel>
                  <StackPanel uen:Region.Name="Profile"
                              Visibility="Collapsed">
                      <TextBlock Text="Profile" />
                  </StackPanel>
              </Grid>
          </muxc:NavigationView>
      </Grid>
  </Page>
  

7. Displaying content in a ContentControl

• Specify the Region.Name of the nested control and the route of the UserControl to display in the Navigation.Request attached property
  XAML

  <Page x:Class="Playground.Views.ContentControlPage">
      <Grid>
          <Grid.RowDefinitions>
              <RowDefinition />
              <RowDefinition Height="Auto" />
          </Grid.RowDefinitions>
              <Button Content="Show profile"
                      uen:Navigation.Request="./Info/Profile" />
              <ContentControl uen:Region.Attached="True"
                              uen:Region.Name="Info"
                              Grid.Row="1" />
      </Grid>
  </Page>
  
  <UserControl x:Class="Playground.Views.ProfileUserControl">
  …
  </UserControl>