Passing argument(s) to a nested Navigation architecture component graph

Question

How does one pass argument(s) to a nested Navigation architecture component graph?

Let's say I construct my navigation graph to navigate from FragmentA --> Nested, where Nested contains FragmentB --> FragmentC...

If this was a pure FragmentA --> FragmentB... graph, I would just set up the navigation with FragmentADirections.actionFragmentAToFragmentB(argument = foo). But that action takes zero arguments as soon as you turn B --> C into Nested...

So what am I supposed to do?

Answer 1

Global actions might be a way but I didn't get that working as I wanted once I extracted the nested graph to its own .xml. But it turned out to be embarrassing simple - just add the arguments manually in code, to your action.

An example related to the question would be:

Save the nested graph to nested_graph.xml, it will look something like

<navigation
    android:id="@+id/nested_graph"
    app:startDestination="@id/fragmentB"
    ...>

    <fragment 
        android:id="@+id/fragmentB"
        ...>
        <argument
            android:name="foo"
            app:argType="integer"/>
        <action 
            ... // navigation action to FragmentC />
    </fragment>

    <fragment ...  // FragmentC stuff
</navigation>

To pass arguments to nested_graph.xml from a different graph, say root_graph.xml do

<navigation
    android:id="@+id/root_graph"
    app:startDestination="@id/fragmentA"
    ...>

    <fragment 
        android:id="@+id/fragmentA"
        ... >
        <action
            android:id="@+id/action_fragmentA_to_nested_graph"
            app:destination="@id/nested_graph">
            <argument
                android:name="foo"
                app:argType="integer"/>
        </action>
    </fragment>
    <include app:graph="@navigation/nested_graph"/>
</navigation>

In other words, just add the same <argument ... /> to the root_graph action as you expect to receive in the nested_graph.