The Navigation component uses a navigation graph to manage your app's navigation. A navigation graph is a resource file that contains all of your app's destinations along with the logical connections, or actions, that users can take to navigate from one destination to another. You can manage your app's navigation graph using the Navigation Editor in Android Studio.
This topic contains best practices and recommendations for designing your app's navigation graphs.
Top-level navigation graph
Your app’s top-level navigation graph should start with the initial destination the user sees when launching the app and should include the destinations that they see as they move about your app.
Figure 1. A top-level navigation graph.
Login flows, wizards, or other sub-flows within your app are usually best
nested navigation graphs.
By nesting self-contained sub-navigation flows in this way, the main flow of
your app’s UI is easier to comprehend and manage. In addition, nested graphs are
reusable. They also provide a level of encapsulation—destinations outside of the
nested graph do not have direct access to any of the destinations within the
nested graph. Instead, they should
to the nested graph itself, where the internal logic can change without
affecting the rest of the graph.
Using the top-level navigation graph from figure 1 as an example, suppose you wanted to require the user to see the title_screen and register screens only when the app is launched for the first time. Afterwards, the user information is stored, and in subsequent launches of the app, you should take them straight to the match screen. As a best practice, you should set the match screen as the start destination of the top-level navigation graph and move the title and register screens into a nested graph, as shown in figure 2:
Figure 2. The top-level navigation graph now contains a nested graph.
When the match screen launches, you can check to see if there is a registered user. If the user isn't registered, you can navigate the user to the registration screen. For more information on conditional navigation scenarios, see Conditional navigation.
Another way to modularize your graph structure is to include one graph within
<include> element in the parent navigation graph. This allows the
included graph to be defined in a separate module or project altogether, which
Navigation across library modules
If your app depends on library modules,
which have a navigation graph contained therein, you can reference these
navigation graphs using an
For more information, see Navigation best practices for multi-module projects.
Any destination in your app that can be reached through more than one path should have a corresponding global action defined to navigate to that destination. Global actions can be used to navigate to a destination from anywhere.
Let's apply this to our library module sample, which has the same action defined in both the win and game over destinations. You should extract these common actions to a single global action and reference them from both destinations, as shown in the following example:
<?xml version="1.0" encoding="utf-8"?> <navigation xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:id="@+id/in_game_nav_graph" app:startDestination="@id/in_game"> <!-- Action back to destination which launched into this in_game_nav_graph--> <action android:id="@+id/action_pop_out_of_game" app:popUpTo="@id/in_game_nav_graph" app:popUpToInclusive="true" /> <fragment android:id="@+id/in_game" android:name="com.example.android.gamemodule.InGame" android:label="Game"> <action android:id="@+id/action_in_game_to_resultsWinner" app:destination="@id/results_winner" /> <action android:id="@+id/action_in_game_to_gameOver" app:destination="@id/game_over" /> </fragment> <fragment android:id="@+id/results_winner" android:name="com.example.android.gamemodule.ResultsWinner" /> <fragment android:id="@+id/game_over" android:name="com.example.android.gamemodule.GameOver" android:label="fragment_game_over" tools:layout="@layout/fragment_game_over" /> </navigation>
See Global actions in the navigation docs to learn more and examples of how to use global actions in your fragments.