Native Frame Navigation

Introduction

This article discusses the particularities of the native Frame navigation in detail.

It is recommended to be familiar with the concept of navigation in UWP, here are some good starting points:

Native Frame Navigation

On Android and iOS, there is the option to enable native frame navigation. Enabling this feature replaces the default styles and templates of the controls below:

  • Windows.UI.Xaml.Controls.Frame*
  • Windows.UI.Xaml.Controls.CommandBar
  • Windows.UI.Xaml.Controls.AppBarButton

This feature can be enabled by calling the method below, typically in the constructor of your App class in App.xaml.cs:

#if __IOS__ || __ANDROID__
    Uno.UI.FeatureConfiguration.Style.ConfigureNativeFrameNavigation();
#endif
Note

It is recommended to enable this feature in order to provide a more native user experience.

CommandBar and AppBarButton

In essence, by enabling this, a custom renderer will be used as the control template. This renderer injects the native control into the app, and maps dependency properties (colors, content/icon, ...) and events (clicked), between the UWP controls and the native ones:

UWP Control Native Android Control Native iOS Control
CommandBar android.widget.Toolbar UIKit.UINavigationBar
AppBarButton android.view.MenuItem UIKit.UIBarButtonItem

As such, you can have the look and feel of the native control, including features like native swipe to go back on iOS, while programming against the UWP API. However, you are no longer able to customize the control template.

Frame

The Frame also uses a custom presenter for its control template. On iOS, this presenter creates an UINavigationController, and keeps its states in sync with its Frame. It also creates a UIViewController for each Page that gets navigated. On iOS and on Android, it also manages the state of back button on the CommandBar, if it is presents on a Page.

Helpers

There is a FrameNavigationHelper that is in place to expose useful properties and methods related to Frame-based navigation logic. It contains the following helper methods:

Method Return Type Description
GetCurrentEntry(Frame) PageStackEntry Returns the PageStackEntry for the currently displayed Page within the given frame.
GetInstance(PageStackEntry) Page Returns the actual Page instance of the given entry.
CreateNavigationEventArgs(...) NavigationEventArgs Creates a new instance of NavigationEventArgs/>

Platform Specifics

  • Android: Tapping the CommandBar's back button, system back button, or performing the sweep gesture will trigger SystemNavigationService.BackRequested. It's the responsibility of the application's navigation controller to eventually call Frame.GoBack().
  • iOS: Tapping the back button automatically triggers a back navigation on the native UINavigationController (which is part of the native Frame implementation). The Frame will raise the Navigated event, and its state will automatically be updated to reflect the navigation. The navigation can't be intercepted or canceled.
  • all non-Windows platforms: Uno.UI.FeatureConfiguration.Page.IsPoolingEnabled can be set to enable reuse of Page instances. Enabling this allows the pages in the forward stack to be recycled when stack is modified, which can improve performance of Frame navigation.
  • Android: On mobile, the pages in the back stack are still preserved in the visual tree for performance reasons. This feature can be disabled on Android by setting Uno.UI.FeatureConfiguration.NativeFramePresenter.AndroidUnloadInactivePages = true.
  • WASM: SystemNavigationManager.AppViewBackButtonVisibility needs to be set to Visible to intercept the browser back navigation. The intercepted event is forwarded to SystemNavigationService.BackRequested. It's the responsibility of the application's navigation controller to eventually call Frame.GoBack().

Additional Resources