Why is my app Crashing with RecyclerView?-CodePudding

I'm doing a recycler method in my android studio project but i have a problem.

Everytime i'm trying to findViewById my application is crashing.

Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference

And i don't understand why because i'm creating my view in the good way.

public View onCreateView(@NonNull LayoutInflater inflater,
                     ViewGroup container, Bundle savedInstanceState) {

    view = inflater.inflate(R.layout.fragment_carrito, container, false);
    return view;
}

And i'm trying to continue with that

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);

        ...

        Log.e("test : ",Integer.toString(R.id.recyclerBuy));
        recyView = view.findViewById(R.id.recyclerBuy);
/*        recyView.setLayoutManager(new GridLayoutManager(getContext(),RecyclerView.VERTICAL));
        recyView.setAdapter(buyAdapter);
 */
    }

But i'm crashing at the line recyView = view.findViewById(R.id.recyclerBuy);. My R.id.recyclerBuy is not empty.

And here is my RecyclerView

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".ui.carrito.CarritoFragment">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@ id/recyclerBuy"
        android:layout_width="match_parent"
        android:layout_height="550dp"
        android:layout_marginBottom="88dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent" />

        ...

</androidx.constraintlayout.widget.ConstraintLayout>

Anyone have a clue why i'm crashing everytime ?

CodePudding user response：

This happens because onAttach() callback is called before onCreateView().

The easiest way to fix the issue is placing the code where you finding your RecyclerView in onCreateView(). Something like:

public View onCreateView(@NonNull LayoutInflater inflater,
                 ViewGroup container, Bundle savedInstanceState) {

    view = inflater.inflate(R.layout.fragment_carrito, container, false);

    recyView = view.findViewById(R.id.recyclerBuy);
    // here you recyView won't be null

    return view;
}

A good article about fragments lifecycle: https://medium.com/androiddevelopers/the-android-lifecycle-cheat-sheet-part-iii-fragments-afc87d4f37fd