Android Navigation Component: Introduction, Usage, and Source Code Analysis

Google I/O 2018 introduced Android Jetpack, which includes the Navigation component to simplify fragment stack management, enable deep links, and provide type‑safe argument passing.

Why use Navigation? It eliminates IllegalStateException errors, supports direct fragment navigation via deeplinks, and offers safer parameter transmission.

Setup – Add the following Gradle dependencies (replace the version as needed):

dependencies {
    nav_version = '1.0.0-alpha01'
    implementation "android.arch.navigation:navigation-fragment:$nav_version"
    implementation "android.arch.navigation:navigation-ui:$nav_version"
}

Define a navigation graph (nav_graph.xml) that declares fragments and actions:

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_graph"
    app:startDestination="@id/mainFragment">

    <fragment
        android:id="@+id/mainFragment"
        android:name="com.jd.demo.ui.main.MainFragment"
        android:label="main_fragment"
        tools:layout="@layout/main_fragment_2">
        <action
            android:id="@+id/action_to_mainFragment2"
            app:destination="@+id/mainFragment2"
            app:enterAnim="@anim/slide_in_right"
            app:exitAnim="@anim/slide_out_left"
            app:popEnterAnim="@anim/slide_in_left"
            app:popExitAnim="@animslide_out_right" />
    </fragment>

    <fragment
        android:id="@+id/mainFragment2"
        android:name="com.jd.demo.ui.main.MainFragment2"
        android:label="main_fragment_2"
        tools:layout="@layout/main_fragment_2" />
</navigation>

In the activity layout, host the navigation graph with NavHostFragment:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/my_nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph" />
</LinearLayout>

Navigate between fragments in Kotlin:

val view = inflater.inflate(R.layout.main_fragment_3, container, false)
val button1 = view.findViewById<Button>(R.id.button3)
button1.setOnClickListener { v ->
    Navigation.findNavController(v).navigate(R.id.action_mainFragment2_to_mainFragment1)
}
return view

Pass data using a Bundle:

Bundle bundle = new Bundle()
bundle.putString("amount", amount)
Navigation.findNavController(view).navigate(R.id.confirmationAction, bundle)

Or use the Safe Args Gradle plugin for type‑safe arguments:

val action = SpecifyAmountFragmentDirections.confirmationAction()
action.setAmount(amount)
Navigation.findNavController(view).navigate(action)

Configure deep links in the navigation XML:

<deepLink app:uri="www.jd.com" />
<deepLink app:uri="www.jd.com.*" />
<deepLink app:uri="www.jd.com/{myarg}" android:autoVerify="true" />

Override onSupportNavigateUp in the host activity to handle back navigation correctly:

@Override
public boolean onSupportNavigateUp() {
    return Navigation.findNavController(this, R.id.my_nav_host_fragment).navigateUp();
}

Source‑code analysis – NavHostFragment creates a NavController in onCreate and a FrameLayout in onCreateView to host destinations. It registers the controller with the view hierarchy so that Navigation.findNavController can locate it.

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Context context = getContext();
    mNavController = new NavController(context);
    mNavController.getNavigatorProvider().addNavigator(createFragmentNavigator());
}

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    FrameLayout frameLayout = new FrameLayout(inflater.getContext());
    frameLayout.setId(getId());
    return frameLayout;
}

The NavController parses the navigation XML, builds a graph of NavDestination objects, and delegates actual navigation actions to concrete implementations such as FragmentNavigator and ActivityNavigator. The article concludes that Navigation offers powerful, safe, and visual navigation capabilities, including deep links, and encourages developers to adopt Kotlin and KTX extensions.