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Navigate with feature modules

The Dynamic Navigator library extends the functionality of the Jetpack Navigation component to work with destinations that are defined in feature modules. This library also provides seamless installation of on-demand feature modules when navigating to these destinations.

Setup

To support feature modules, use the following dependencies in your app module's build.gradle file:

dependencies {
    def nav_version = "2.3.1"

    api "androidx.navigation:navigation-fragment-ktx:$nav_version"
    api "androidx.navigation:navigation-ui-ktx:$nav_version"
    api "androidx.navigation:navigation-dynamic-features-fragment:$nav_version"
}

Note that the other Navigation dependencies should use api configurations so that they are available to your feature modules.

Basic usage

To support feature modules, first change all instances of NavHostFragment in your app to androidx.navigation.dynamicfeatures.fragment.DynamicNavHostFragment:

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/nav_host_fragment"
    android:name="androidx.navigation.dynamicfeatures.fragment.DynamicNavHostFragment"
    app:navGraph="@navigation/nav_graph"
    ... />

Next, add an app:moduleName attribute to any <activity>, <fragment>, or <navigation> destinations in your com.android.dynamic-feature module's navigation graphs that are associated with a DynamicNavHostFragment. This attribute tells the Dynamic Navigator library that the destination belongs to a feature module with the name that you specify.

<fragment
    app:moduleName="myDynamicFeature"
    android:id="@+id/featureFragment"
    android:name="com.google.android.samples.feature.FeatureFragment"
    ... />

When you navigate to one of these destinations, the Dynamic Navigator library first checks if the feature module is installed. If the feature module is already present, your app navigates to the destination as expected. If the module isn't present, your app shows an intermediate progress fragment destination as it installs the module. The default implementation of the progress fragment shows a basic UI with a progress bar and handles any installation errors.

two loading screens that show UI with a progress bar when navigating
         to a feature module for the first time
Figure 1. UI showing a progress bar when a user navigates to an on-demand feature for the first time. The app displays this screen as the corresponding module downloads.

To customize this UI, or to manually handle installation progress from within your own app screen, see the Customize the progress fragment and Monitor the request state sections in this topic.

Destinations that don't specify app:moduleName continue to work without changes and behave as though your app uses a regular NavHostFragment.

Customize the progress fragment

You can override the progress fragment implementation for each navigation graph by setting the app:progressDestination attribute to the ID of the destination you want to use for handling installation progress. Your custom progress destination should be a Fragment that derives from AbstractProgressFragment. You must override the abstract methods for notifications about installation progress, errors, and other events. You can then show installation progress in a UI of your choice.

The default implementation's DefaultProgressFragment class uses this API to show installation progress.

Monitor the request state

The Dynamic Navigator library enables you to implement a UX flow similar to the one in UX best practices for on-demand delivery, in which a user stays in the context of a previous screen while waiting for installation to finish. This means that you don't need to show an intermediate UI or progress fragment at all.

screen that shows a bottom nav bar with an icon that indicates
         that a feature module is downloading
Figure 2. Screen that shows download progress from a bottom navigation bar.

In this scenario, you are responsible for monitoring and handling all installation states, progress changes, errors, and so on.

To initiate this non-blocking navigation flow, pass a DynamicExtras object that contains a DynamicInstallMonitor to NavController.navigate(), as shown in the following example:

Kotlin

val navController = ...
val installMonitor = DynamicInstallMonitor()

navController.navigate(
    destinationId,
    null,
    null,
    DynamicExtras(installMonitor)
)

Java

NavController navController = ...
DynamicInstallMonitor installMonitor = new DynamicInstallMonitor();

navController.navigate(
    destinationId,
    null,
    null,
    new DynamicExtras(installMonitor);
)

Immediately after calling navigate(), you should check the value of installMonitor.isInstallRequired to see if the attempted navigation resulted in a feature module installation.

  • If the value is false, you're navigating to a normal destination and don't need to do anything else.
  • If the value is true, you should start observing the LiveData object that is now in installMonitor.status. This LiveData object emits SplitInstallSessionState updates from the Play Core library. These updates contain installation progress events that you can use to update the UI. Remember to handle all relevant statuses as outlined in the Play Core guide, including asking for user confirmation if necessary.

    Kotlin

    val navController = ...
    val installMonitor = DynamicInstallMonitor()
    
    navController.navigate(
      destinationId,
      null,
      null,
      DynamicExtras(installMonitor)
    )
    
    if (installMonitor.isInstallRequired) {
      installMonitor.status.observe(this, object : Observer<SplitInstallSessionState> {
          override fun onChanged(sessionState: SplitInstallSessionState) {
              when (sessionState.status()) {
                  SplitInstallSessionStatus.INSTALLED -> {
                      // Call navigate again here or after user taps again in the UI:
                      // navController.navigate(destinationId, destinationArgs, null, null)
                  }
                  SplitInstallSessionStatus.REQUIRES_USER_CONFIRMATION -> {
                      SplitInstallManager.startConfirmationDialogForResult(...)
                  }
    
                  // Handle all remaining states:
                  SplitInstallSessionStatus.FAILED -> {}
                  SplitInstallSessionStatus.CANCELED -> {}
              }
    
              if (sessionState.hasTerminalStatus()) {
                  installMonitor.status.removeObserver(this);
              }
          }
      });
    }
    

    Java

    NavController navController = ...
    DynamicInstallMonitor installMonitor = new DynamicInstallMonitor();
    
    navController.navigate(
      destinationId,
      null,
      null,
      new DynamicExtras(installMonitor);
    )
    
    if (installMonitor.isInstallRequired()) {
      installMonitor.getStatus().observe(this, new Observer<SplitInstallSessionState>() {
          @Override
          public void onChanged(SplitInstallSessionState sessionState) {
              switch (sessionState.status()) {
                  case SplitInstallSessionStatus.INSTALLED:
                      // Call navigate again here or after user taps again in the UI:
                      // navController.navigate(mDestinationId, mDestinationArgs, null, null);
                      break;
                  case SplitInstallSessionStatus.REQUIRES_USER_CONFIRMATION:
                      SplitInstallManager.startConfirmationDialogForResult(...)
                      break;
    
                  // Handle all remaining states:
                  case SplitInstallSessionStatus.FAILED:
                      break;
                  case SplitInstallSessionStatus.CANCELED:
                      break;
              }
    
              if (sessionState.hasTerminalStatus()) {
                  installMonitor.getStatus().removeObserver(this);
              }
          }
      });
    }
    

When the installation finishes, the LiveData object emits a SplitInstallSessionStatus.INSTALLED status. You should then call NavController.navigate() again. Since the module is now installed, the call now succeeds, and the app navigates to the destination as expected.

After reaching a terminal state, such as when installation completes or when installation fails, you should remove your LiveData observer to avoid memory leaks. You can check if the status represents a terminal state by using SplitInstallSessionStatus.hasTerminalStatus().

See AbstractProgressFragment for an example implementation of this observer.

Included graphs

The Dynamic Navigator library supports including graphs that are defined in feature modules. To include a graph that is defined in a feature module, do the following:

  1. Use <include-dynamic/> instead of <include/>, as shown in the following example:

    <include-dynamic
        android:id="@+id/includedGraph"
        app:moduleName="includedgraphfeature"
        app:graphResName="included_feature_nav"
        app:graphPackage="com.google.android.samples.dynamic_navigator.included_graph_feature" />
    
  2. Inside <include-dynamic ... />, you must specify the following attributes:

    • app:graphResName: the name of the navigation graph resource file. The name is derived from the graph's file name. For example, if the graph is in res/navigation/nav_graph.xml, the resource name is nav_graph.
    • android:id - the graph destination ID. The Dynamic Navigator library ignores any android:id values that are found in the root element of the included graph.
    • app:moduleName: the feature module name.

Limitations

  • Dynamically-included graphs don't currently support deep links.
  • Dynamically-loaded nested graphs (that is, a <navigation> element with an app:moduleName) don't currently support deep links.

Android Studio support

To use the Navigation editor with the Dynamic Navigator library, you must use version 4.0 or higher of Android Studio.

In older versions of Android Studio, you should work directly with the XML for the navigation graph. Opening a navigation graph that contains any of the tags or attributes described in this topic might otherwise cause exceptions and other undefined behavior.