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?
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.
If you do not want to create a separated xml for the nested graph you can override destination argument in an action as android developers says here. I just test it for use with navigation graph view model scope and it worked perfectly. I am using Version 2.2.0-alpha03 of navigation component. After added those params to the action action_inboxFragment_to_conversation_graph, now the InboxFragmentDirections.ActionInboxFragmentToConversationGraph is generated correctly.
<?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/messages_graph"
app:startDestination="@id/inboxFragment">
<fragment
android:id="@+id/inboxFragment"
android:name="com.wlpr.docfinder.ui.fragment.InboxFragment"
android:label="fragment_inbox"
tools:layout="@layout/fragment_inbox" >
<action
android:id="@+id/action_inboxFragment_to_conversation_graph"
app:destination="@id/conversation_graph">
<argument
android:name="participantName"
android:defaultValue="Conversation"
app:argType="string"
app:nullable="true" />
<argument
android:name="documentsCount"
android:defaultValue="1"
app:argType="integer" />
</action>
</fragment>
<navigation
android:id="@+id/conversation_graph"
android:label="conversationGraph"
app:startDestination="@id/conversationFragment">
<fragment
android:id="@+id/conversationFragment"
android:name="com.wlpr.docfinder.ui.fragment.ConversationFragment"
android:label="fragment_conversation"
tools:layout="@layout/fragment_conversation">
<action
android:id="@+id/action_conversationFragment_to_reportingDetailsFragment"
app:destination="@id/reportingDetailsFragment" />
<argument
android:name="participantName"
android:defaultValue="Conversation"
app:argType="string"
app:nullable="true" />
<argument
android:name="documentsCount"
android:defaultValue="1"
app:argType="integer" />
</fragment>
<!-------- more fragments... -------->
</navigation>
