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.

Worser

How do you pass the value?.. you didn't include that – Diaeresis

@Diaeresis ``` ClassNameDirections.ActionName action = ClassNameDirections.actionName( character); Navigation.findNavController(v).navigate(action); ``` – Worser

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

Diaeresis

Answer 2

I don't know about safeArgs but if you don't get an answer using safeArgs, that's how you do it with normal bundle.

if you don't know you can send a bundle containing your data along the navigation action as a second parameter to the method.
like that

char char_value = 'a' ;
Bundle data = new Bundle() ;
data.putChar("key",char_value);
NavHostFragment.findNavController(this)
                    .navigate(R.id.action_bookDescriptionFragment_to_bookListFragment,data);

and in booklistFragment you just call getArguments() anywhere inside the fragment to get this bundle like this

public class BookListFragment extends Fragment {
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
    Bundle data = getArguments() ;
    char receivedChar = data.getChar("key",'z'); // 'z' is a default value incase it didn't find the key you're looking for it returns 'z'
    }

where you can put in a bundle a variety of things, just type 'put' and see what the AutoComplete suggests.

incase of using the bundle, you don't need to add the argument part in the nav_graph xml.

Cornstarch