Passing an argument between two fragments each of them in a different Navigation Graph

Question

Using Android Navigation Component. I have two Navigation Graphs (each of them with their own flow), lets say navigation graphs A and B. I navigate successfully from A to B, but I can't manage to pass an argument from the last Fragment included in graph A to the start Fragment that belongs to graph B.

I am able to pass arguments between fragments that belong to the same graph, but the function to set the arguments is not been generated when navigating between to navigation graphs.

I am trying to accomplish that using safeargs.

Here is the navigation graphs code:

Navigation Graph A:

<navigation android:id="@+id/nav_graph_a"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        app:startDestination="@id/fragment1">

<fragment
    android:id="@+id/fragment1"
    android:name="com.mypackage.fragments.Fragment1"
    android:label="Fragment1">
    <action
        android:id="@+id/action_fragment1_to_fragment2"
        app:destination="@id/fragment2"/>

</fragment>

<fragment
    android:id="@+id/fragment2"
    android:name="com.mypackage.fragments.Fragment2"
    android:label="Fragment2">
    <argument
        android:name="thisArgumentAlwaysArrive"
        android:defaultValue="null"
        app:argType="string"/>
    <action
        android:id="@+id/action_fragment2_to_nav_graph_b"
        app:destination="@id/nav_graph_b"/>
</fragment>

<include app:graph="@navigation/nav_graph_b"/>

Navigation Graph B:

<navigation android:id="@+id/nav_graph_b"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        app:startDestination="@id/fragment3">

<fragment
    android:id="@+id/fragment3"
    android:name="com.mypackage.fragments.Fragment3"
    android:label="Fragment3">

    <argument
        android:name="thisArgumentNeverArrive"
        app:argType="string"/>
</fragment>

Any idea on how to accomplish this?

Answer 1

As stated in the documentation:

Note: Safe Args do not support cross-module navigation, as there is no direct action to the destination. In the previous example, although a Directions class would be generated for the target destination in settings, you aren't able to access the generated class from the classpath of the list module.

But you can use a bundle instead of nav_args like this:

From

FristFragmentDirections.actionFirstFragmentToSecondFragment(your_parameter).let { action ->
    findNavController().navigate(action)
}

To

FristFragmentDirections.actionFirstFragmentToSecondFragment().let { action ->
    findNavController().navigate(
        action.actionId,
        Bundle().apply { putString("parameter_key", your_parameter) }
    )
}

Answer 2

Safe Args is the plugin for Gradle that creates the classes ClassArgs for the destinations. The default controller provides a way to navigate to another NavGraph, in this case there is an implementation of a Navigator called NavGraphNavigator. This navigator provides you with a navigate(NavGraph destination,Bundle args) function that passes the arguments to the start fragment.

So, the best way I have found to do what you are trying to achieve is to use the generated class to generate a bundle with the needed arguments.

var myBundle = YourFragmentIdInNavGraphArgs.Builder(var args..).toBundle()

and then use the default NavController to navigate to a navGraph destination like this.

view.findNavController().navigate(R.id.your_action_to_nav_graph_id,myBundle)

the implementation of the Navigator will take care of passing the arguments to the start fragment on the destination.

Hope it helps to some one.