Cannot pass arguments since Fragment to child Fragment

Question

I have a Fragment A containing a Fragment B.

I want to pass an argument to Fragment B from Fragment A when Fragment A is in the onActivityCreated lifecycle (because I have a data coming from a viewmodel that arrives at this moment).

In my Fragment B I cannot get the argument. I have a null exception.

Do you have a solution to my problem?

Here is my code

Fragment A

class FragmentA: Fragment() {

    private lateinit var fragmentB: FragmentB

    /**
     * @inheritdocs
     */
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_a, container, false)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        this.fragmentB = FragmentB()
        val transaction = childFragmentManager.beginTransaction()
        transaction.add(R.id.fragmentB, fragmentB).commit()
    }

    /**
     * @inheritdocs
     */
    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        val args = Bundle()
        args.putString("name", "test")
        this.fragmentB.arguments = args
    }
}

FragmentB

class FragmentB: Fragment() {


    /**
     * @inheritdocs
     */
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_b, container, false)
    }

    /**
     * @inheritdocs
     */
    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        var name = this.arguments?.getString("name")!!
    }
}

fragment_a.xml

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment
        android:id="@+id/fragmentB"
        android:name="com.test.view.FragmentB"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

score 2 · Answer 1 · answered Nov 19 '19 at 09:52

You have declared Fragment in your xml layout. This means it gets created without the args. If you are adding Fragment from code, then you don't need to declare it in xml.

So just change your xml to this:

<androidx.constraintlayout.widget.ConstraintLayout       
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <FrameLayout
        android:id="@+id/fragmentB"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

So I should instantiate the fragmentB in the onCreateView from FragmentA class ? — Dev Loots, Nov 19 '19 at 09:55
@vilpe89 is correct .Yes , add it dynamically with args. It will work. — ROHIT LIEN, Nov 19 '19 at 09:59
Thanks, I forgot to change the fragment attribute by FrameLayout — Dev Loots, Nov 19 '19 at 10:05

score 1 · Accepted Answer · answered Nov 19 '19 at 10:05

Inside your fragment B implement static method to initialize the fragment like bellow.

public static FragmentB newInstance(string x) {
  FragmentB f = new FragmentB ();

  Bundle args = new Bundle();
  args.putInt("name", x);
  f.setArguments(args);
  return f;
}

you can use this method in FragmentA

Cannot pass arguments since Fragment to child Fragment

3 Answers3