androidandroid-jetpackandroid-architecture-componentsandroid-architecture-navigation

Android Navigation Component load 2 nested Fragments into Parent Fragment


I have a Comparator Screen which is a Fragment that is splitted into 2 sub-screens. Before using Navigation Component I could easily just:

 private void initializeFragments() {

        FoodComparatorFragment comparatorFragment1 = new FoodComparatorFragment();
        FoodComparatorFragment comparatorFragment2 = new FoodComparatorFragment();

        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.comparator_fragment_1, comparatorFragment1);
        transaction.add(R.id.comparator_fragment_2, comparatorFragment2);

        transaction.commit();
    }

However, I don't know how I should perform this operation with the Navigation Component WITHOUT using explicitly the FragmentManager.


Solution

  • By default with navigation components there is one NavHostFragment hosted by the main activity for one activity/many fragments model. For many activities/fragments model, each activity has its own NavHostFragment/NavGraph.

    Here we'll consider one activity, many fragments model, where one of these fragments is the Comparator Screen (parent fragment) that is splitted into 2 sub-screens/fragments.

    But the NavHostFragment can only host a single fragment at a time; so the idea here is to have two NavHostFragments within the comparator/parent fragment.


    Considering the below example:

    • We have a MainActivity that hosts two fragments (HomeFragment, ParentFragment).
    • The ParentFragment is the comparator with two NavHostFragments, each can host a single fragment; the top one is TopFragment, the bottom is BottomFragment.
    • There is an action to go from the HomeFragment to the ParentFragment
    • There is int argument sent to each sub-screen, the Top/Bottom fragments, done by sending arguments to the sub-screens along with the action from the HomeFragment to the ParentFragment; they will be displayed on TextViews on the screen.
    MainActivity (1 NavHostFragments/NavGraph) ->> nav_host_fragment_activity_main
        |
        |---- HomeFragment
        |
        |---- ParentFragment (2 NavHostFragments/NavGraphs) ->> top_nav_host_fragment & bottom_nav_host_fragment
        |       |
        |       |---- TopFragment
        |       |
        |       |---- BottomFragment
    

    Now we have 3 NavGraphs:

    Main (mobile_navigation.xml):

    <?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/mobile_navigation"
        app:startDestination="@+id/navigation_home">
    
        <fragment
            android:id="@+id/navigation_home"
            android:name="com.example....HomeFragment"
            android:label="@string/title_home"
            tools:layout="@layout/fragment_home">
    
            <action
                android:id="@+id/action_homeFragment_to_parentFragment"
                app:destination="@id/navigation_parent"
                app:popUpTo="@id/navigation_home"
                app:popUpToInclusive="false" />
    
        </fragment>
    
        <fragment
            android:id="@+id/navigation_parent"
            android:name="com.example....ParentFragment"
            android:label="@string/title_parent"
            tools:layout="@layout/fragment_parent">
    
            <argument
                android:name="top_arg"
                android:defaultValue="-1"
                app:argType="integer" />
    
            <argument
                android:name="bottom_arg"
                android:defaultValue="-1"
                app:argType="integer" />
    
        </fragment>
    
    </navigation>
    

    enter image description here

    And in ParentFragment, another two NavGraphs, each for a sub-screen:

    For the 1st sub-screen (top_navigation.xml):

    <?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/top_navigation"
        app:startDestination="@+id/top_fragment">
    
        <fragment
            android:id="@+id/top_fragment"
            android:name="com.example.....TopFragment"
            tools:layout="@layout/fragment_top">
    
            <argument
                android:name="arg"
                android:defaultValue="-1"
                app:argType="integer" />
    
        </fragment>
    
    </navigation>
    

    For the 2nd sub-screen (bottom_navigation.xml):

    <?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/bottom_navigation"
        app:startDestination="@+id/bottom_fragment">
    
        <fragment
            android:id="@+id/bottom_fragment"
            android:name="com.example.....BottomFragment"
            tools:layout="@layout/fragment_bottom">
    
            <argument
                android:name="arg"
                android:defaultValue="-1"
                app:argType="integer" />
    
        </fragment>
    
    </navigation>
    

    Layouts:

    activity_main.xml

    <?xml version="1.0" encoding="utf-8"?>
    <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    
        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/nav_host_fragment_activity_main"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:defaultNavHost="true"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:navGraph="@navigation/mobile_navigation" />
    
    </androidx.constraintlayout.widget.ConstraintLayout>
    

    fragment_parent.xml

    <?xml version="1.0" encoding="utf-8"?>
    <androidx.constraintlayout.widget.ConstraintLayout 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=".ui.fragments.HomeFragment">
    
        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/top_nav_host_fragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:background="@color/teal_200"
            app:layout_constraintBottom_toTopOf="@id/bottom_nav_host_fragment"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    
        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/bottom_nav_host_fragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:background="@color/purple_200"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/top_nav_host_fragment" />
    
    
    </androidx.constraintlayout.widget.ConstraintLayout>
    

    fragment_top/bottom.xml are straightforward

    fragment_top.xml:

    <?xml version="1.0" encoding="utf-8"?>
    <androidx.constraintlayout.widget.ConstraintLayout 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=".ui.fragments.ParentFragment">
    
        <TextView
            android:id="@+id/textview"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:textAlignment="center"
            android:text="top fragment"
            android:textSize="20sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    
    </androidx.constraintlayout.widget.ConstraintLayout>
    

    The NavGraph of the Top & Bottom fragments will be set programmatically in order to allow passing the arguments from the main NavGraph to the sub-screens' NavGraphs.

    Now in the HomeFragment, there is a button to go to the ParentFragment with the action defined in the NavGraph, which sends the arguments needed for both sub-screens:

    findNavController().navigate(
        HomeFragmentDirections.actionHomeFragmentToParentFragment()
        .setTopArg(100)
        .setBottomArg(200))
    

    Then receive the arguments at the ParentFragment with the SafeArgs:

    // get fragment arguments through SafeArgs
    val args = ParentFragmentArgs.fromBundle(requireArguments()) 
    val bottomBundle = Bundle()
    bottomBundle.putInt("arg", args.bottomArg)
    val topBundle = Bundle()
    topBundle.putInt("arg", args.topArg)
    // setting the navGraph of the top/bottom NavHostFragments, 
    // and pass the argument along as a bundle.
    val bottomNavHostFragment =
        childFragmentManager.findFragmentById(R.id.bottom_nav_host_fragment)
                as NavHostFragment
    bottomNavHostFragment.navController.setGraph(R.navigation.bottom_navigation, bottomBundle)
    
    val topNavHostFragment = childFragmentManager.findFragmentById(R.id.top_nav_host_fragment)
            as NavHostFragment
    topNavHostFragment.navController.setGraph(R.navigation.top_navigation, topBundle)
    

    Once more at the destination top/bottom sub-screens, get the argument with safeArgs, and set it to the TextView:

    // TopFragment
    textView.text = TopFragmentArgs.fromBundle(
        requireArguments()
    ).arg.toString()
    
    // BottomFragment
    textView.text = BottomFragmentArgs.fromBundle(
        requireArguments()
    ).arg.toString()
    

    enter image description here