Xaml Navigation

Prism allows you to declare your navigation directly inside your Xaml via a Markup Extension. This approach really helps with basic navigation scenarios, and can also help clean up your ViewModels.

Defining your navigation path in Xaml

To define navigation from within your Xaml, simply add the prism namespace to your Page

<Page xmlns:prism="http://prismlibrary.com">

And then add the Markup Extension to any Command property (buttons, tap gesture recognizers, etc.)

<!-- normal navigation -->
<Button Command="{prism:NavigateTo 'path/to/navigate'}" />

<!-- replace a page on the stack -->
<Button Command="{prism:NavigateTo '../navigate'}" />

Navigating back OR back to the root page will be done via the GoBack extension

<!-- go back one -->
<Button Command="{prism:GoBack}" />

<!-- go back to the root -->
<Button Command="{prism:GoBack ToRoot}" />

Adding NavigationParameters via Xaml

You can also define NavigationParameters to your Xaml in one of three ways.

1: Directly as a CommandParameter Binding.

Note: in order to access it, you need to lookup xamlParam from your NavigationParameters property. This is also statically defined in KnownNavigationParameters.XamlParam

<Button Command="{prism:NavigateTo 'path/to/navigate'}"
        CommandParameter="{Binding Foo}" />

public override void OnNavigatingTo(INavigationParameters parameters)
{
    if(parameters.TryGetValue(KnownNavigationParameters.XamlParam, out object fooObject))
    {
        // do something with fooObject
    }
}

2: As a single navigation parameter

<Button Command="{prism:NavigateTo 'path/to/navigate'}">
    <Button.CommandParameter>
        <prism:NavigationParameter Key="Foo" Value="Some Value" />
    </Button.CommandParameter>
</Button>

3: As a collection of navigation parameters

<Button Command="{prism:NavigateTo 'path/to/navigate'}">
    <Button.CommandParameter>
        <prism:NavigationParameters>
            <prism:NavigationParameter Key="Foo" Value="{Binding SomeBarValue}" />
            <prism:NavigationParameter Key="Fizz" Value="Some Buzz Value" />
        </prism:NavigationParameters>
    </Button.CommandParameter>
</Button>

note: you can also optionally specify a BindingContext on either your NavigationParameters or NavigationParameter.

Controlling CanNavigate

You can control whether or not the user CanNavigate via an attached property. This attached property can be set on any parent object, and Prism will walk the tree until it finds the value. If Prism cannot find a CanNavigate property, it simply assumes true with a single caveat. In order to prevent double-tap issues, Prism's Xaml Navigation tracks if the user has already initiated navigation, if they have, then it prevents them from initiating it again.

<Page>
    <StackLayout prism:Navigation.CanNavigate="{Binding MyCanNavigateProperty}">
        <ContentView>
            <Button Command="{prism:NavigateTo 'path/to/navigate'}"
                    CommandParameter="{Binding Foo}" />
        </ContentView>
    </StackLayout>
</Page>

Defining your Source Page

In the rare case that you need to tell the NavigationService to use a different Page from the one that Xamarin Forms passes into the Markup Extension, you can override the SourcePage

<Button Command="{prism:NavigateTo 'path/to/navigate', SourcePage={x:Reference SomeOtherPage}}" />

One possible scenario is one which you want your Master to use a NavigationPage for the aesthetics of having a title bar, and want to make sure that your Navigation references are navigating from the MasterDetailPage rather than inside of the NavigationPage. In order to achieve this, you'll give your MasterDetailPage an x:Name and supply that to the SourcePage property of the NavigateTo extension.

<MasterDetailPage x:Name="mdp">
  <MasterDetailPage.Master>
    <NavigationPage Title="Menu">
      <x:Arguments>
        <ContentPage Title="Foo">
          <Button Text="ClickMe"
                  Command="{prism:NavigateTo 'NavigationPage/ViewA', SourcePage={x:Reference mdp}}" />
        </ContentPage>
      <x:Arguments>
    </NavigationPage>
  </MasterDetailPage.Master>
</MasterDetailPage>

Extending the markup extensions

If you wish to add additional functionality to your xaml navigation, Prism has made it easy for you to extend both the NavigateTo and GoBack extensions. Some reasons you might want to do this would be to add additional options or simply add debug logging.

public class ExNavigateToExtension : NavigateToExtension
{
    protected override async Task HandleNavigation(INavigationParameters parameters, INavigationService navigationService)
    {
        Debug.WriteLine($"Navigating to: {Name}");
        await base.HandleNavigation(parameters, navigationService);
    }
}