how to pass a value using android navigation if the default value null

Question

I'm using android navigation components with safe args. I set that the argument is null-able and default value as null too.

The problem is when I want to pass any value an error is shown:

required: no arguments
found: Character
reason: actual and formal argument lists differ in length

My fragment XML code:

<fragment
        android:id="@+id/bookListFragment"
        android:name="com.example.bookstory.UI.Fragments.BookListFragment"
        android:label="fragment_book_list"
        tools:layout="@layout/fragment_book_list">
            <argument
            android:name="character"
            app:argType="com.example.bookstory.DAO.Character"
            app:nullable="true"
            android:defaultValue="@null" />
</fragment>

My action:

      <action
            android:id="@+id/action_bookDescriptionFragment_to_bookListFragment"
            app:destination="@id/bookListFragment"
            app:popUpTo="@id/bookListFragment"
            app:popUpToInclusive="true" />

I can't understand what is the problem - when I delete the default value it is OK.

Answer 1

ClassNameDirections.ActionName action = ClassNameDirections.actionName(character); Navigation.findNavController(v).navigate(action);

As your action id is action_bookDescriptionFragment_to_bookListFragment

  <action
        android:id="@+id/action_bookDescriptionFragment_to_bookListFragment"

Then it can be utilized in this navigate() method version that takes in a NavDirections arg:

findNavController().navigate(BookListFragmentDirections.actionBookDescrioptionFragmentToBookListFragment()

This won't pass in a value, but to do so:

As your value is named as character:

 <argument
        android:name="character"
        app:argType="com.example.bookstory.DAO.Character"
        app:nullable="true"
        android:defaultValue="@null" />

Then you can cascade the action with the safeArgs generated setCharacter() method:

findNavController().navigate(BookListFragmentDirections.actionBookDescrioptionFragmentToBookListFragment()
                    .setCharacter("c")

I see that you use safeArgs, but just in case you don't want to use it; you can use this navigate() method version to set the value through a bundle object