Android Java - Receiving null reference error on RecyclerView.setAdapter()-CodePudding

I am receiving the following error: error: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference

Here is my code:

PropertyHome.java:

public class PropertyHome extends AppCompatActivity
{
    private RecyclerView recyclerView;
    private RecyclerView.Adapter recyclerAdapter;
    private RecyclerView.LayoutManager recyclerLayoutManager;

    ...

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        try {
            recyclerView = (RecyclerView)findViewById(R.id.get_property_entry_property_home);

            String[] myRecycler = new String[5];
            myRecycler[0] = "Recycler 1";
            myRecycler[1] = "Recycler 2";
            myRecycler[2] = "Recycler 3";
            myRecycler[3] = "Recycler 4";
            myRecycler[4] = "Recycler 5";

            recyclerAdapter = new GetPropertyRecyclerViewAdapater(myRecycler);
            recyclerView.setLayoutManager(new LinearLayoutManager(this));
            recyclerView.setAdapter(recyclerAdapter);
        }
        catch(Exception e)
        {
            Toast.makeText(PropertyHome.this, "Error: "   e.toString(), Toast.LENGTH_LONG).show();
        }
    }
    ...
}

activity_property_homr.xml:

<?xml version="1.0" encoding="utf-8"?>

<ScrollView 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:layout_width="match_parent"
    android:layout_height="wrap_content"
    tools:layout_editor_absoluteX="1dp"
    tools:layout_editor_absoluteY="1dp"
    tools:context=".MainActivity">

        <LinearLayout
            android:id="@ id/linear_layout"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:onClick="AppLogout"
            android:orientation="vertical"
            android:textAlignment="gravity" >

                <androidx.recyclerview.widget.RecyclerView
                    android:id="@ id/get_property_entry_property_home"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    tools:itemCount="0" />
        </LinearLayout>
</ScrollView>

Layout for displaying each row of the RecyclerView:

GetPropertyRecyclerViewAdapter.java:


public class GetPropertyRecyclerViewAdapater extends RecyclerView.Adapter<GetPropertyRecyclerViewAdapater.ViewHolder>
{
    private String[] dataSet;

    public static class ViewHolder extends RecyclerView.ViewHolder
    {
        public final TextView mTextView;

        public ViewHolder(View v)
        {
            super(v);

            mTextView = (TextView)v.findViewById(R.id.location_property_home);
        }

        public TextView getTextView()
        {
            return mTextView;
        }
    }

    public GetPropertyRecyclerViewAdapater(String[] myDataSet)
    {
        dataSet = myDataSet;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType)
    {
        View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.recycler_view_item, viewGroup, false);

        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, final int position)
    {
        holder.getTextView().setText(dataSet[position]);
    }

    @Override
    public int getItemCount()
    {
        return dataSet.length;
    }
}

recycler_view_item.xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="8dp">

  <TextView
      android:id="@ id/textView"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="20dp"
      android:layout_marginTop="20dp"
      android:text="Price:"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@ id/image_property_home" />

  <TextView
      android:id="@ id/price_property_home"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="10dp"
      android:text="0"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="@ id/textView"
      app:layout_constraintStart_toEndOf="@ id/textView"
      app:layout_constraintTop_toTopOf="@ id/textView" />

  <TextView
      android:id="@ id/textView6"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="20dp"
      android:layout_marginTop="10dp"
      android:text="Location:"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@ id/textView" />

  <TextView
      android:id="@ id/location_property_home"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="10dp"
      android:text="N/A"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="@ id/textView6"
      app:layout_constraintStart_toEndOf="@ id/textView6"
      app:layout_constraintTop_toTopOf="@ id/textView6" />

  <ImageView
      android:id="@ id/imageView"
      android:layout_width="30dp"
      android:layout_height="30dp"
      android:layout_marginStart="20dp"
      android:layout_marginTop="20dp"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@ id/location_property_home"
      app:srcCompat="@drawable/bedroom" />

  <TextView
      android:id="@ id/bedrooms_property_home"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="10dp"
      android:text="0"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="@ id/imageView"
      app:layout_constraintStart_toEndOf="@ id/imageView"
      app:layout_constraintTop_toTopOf="@ id/imageView" />

  <ImageView
      android:id="@ id/imageView2"
      android:layout_width="30dp"
      android:layout_height="30dp"
      android:layout_marginStart="20dp"
      android:layout_marginTop="20dp"
      app:layout_constraintStart_toEndOf="@ id/bedrooms_property_home"
      app:layout_constraintTop_toBottomOf="@ id/location_property_home"
      app:srcCompat="@drawable/bathroom" />

  <TextView
      android:id="@ id/bathrooms_property_home"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="10dp"
      android:text="0"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="@ id/imageView2"
      app:layout_constraintStart_toEndOf="@ id/imageView2"
      app:layout_constraintTop_toTopOf="@ id/imageView2" />

  <ImageView
      android:id="@ id/imageView3"
      android:layout_width="30dp"
      android:layout_height="30dp"
      android:layout_marginStart="20dp"
      android:layout_marginTop="20dp"
      app:layout_constraintStart_toEndOf="@ id/bathrooms_property_home"
      app:layout_constraintTop_toBottomOf="@ id/location_property_home"
      app:srcCompat="@drawable/garage" />

  <TextView
      android:id="@ id/garages_property_home"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="10dp"
      android:text="0"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="@ id/imageView3"
      app:layout_constraintStart_toEndOf="@ id/imageView3"
      app:layout_constraintTop_toTopOf="@ id/imageView3" />

  <ImageView
      android:id="@ id/imageView4"
      android:layout_width="30dp"
      android:layout_height="30dp"
      android:layout_marginStart="20dp"
      android:layout_marginTop="20dp"
      app:layout_constraintStart_toEndOf="@ id/garages_property_home"
      app:layout_constraintTop_toBottomOf="@ id/location_property_home"
      app:srcCompat="@drawable/area" />

  <TextView
      android:id="@ id/area_property_home"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="10dp"
      android:text="0"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="@ id/imageView4"
      app:layout_constraintStart_toEndOf="@ id/imageView4"
      app:layout_constraintTop_toTopOf="@ id/imageView4" />

  <ImageView
      android:id="@ id/image_property_home"
      android:layout_width="wrap_content"
      android:layout_height="200dp"
      android:layout_marginStart="20dp"
      android:layout_marginTop="20dp"
      android:layout_marginEnd="20dp"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toTopOf="parent"
      app:srcCompat="@drawable/placeholder_image" />

  <ImageButton
      android:id="@ id/edit_property_home"
      android:layout_width="48dp"
      android:layout_height="48dp"
      android:scaleType="center"
      app:layout_constraintEnd_toEndOf="@ id/image_property_home"
      app:layout_constraintTop_toTopOf="@ id/image_property_home"
      app:srcCompat="@android:drawable/ic_menu_edit" />

  <ImageButton
      android:id="@ id/delete_property_home"
      android:layout_width="48dp"
      android:layout_height="48dp"
      app:layout_constraintEnd_toStartOf="@ id/edit_property_home"
      app:layout_constraintTop_toTopOf="@ id/image_property_home"
      app:srcCompat="@android:drawable/ic_menu_delete" />

</androidx.constraintlayout.widget.ConstraintLayout>

I've tried my best to find where the error is, but cannot find it.

CodePudding user response：

You missed an important part in your code, setContentView() add it in you onCreate() right after super() call Should be working then

public class PropertyHome extends AppCompatActivity
{
    private RecyclerView recyclerView;
    private RecyclerView.Adapter recyclerAdapter;
    private RecyclerView.LayoutManager recyclerLayoutManager;

    ...

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_property_homr); // add setContentView here
        try {
            recyclerView = (RecyclerView)findViewById(R.id.get_property_entry_property_home);

            String[] myRecycler = new String[5];
            myRecycler[0] = "Recycler 1";
            myRecycler[1] = "Recycler 2";
            myRecycler[2] = "Recycler 3";
            myRecycler[3] = "Recycler 4";
            myRecycler[4] = "Recycler 5";

            recyclerAdapter = new GetPropertyRecyclerViewAdapater(myRecycler);
            recyclerView.setLayoutManager(new LinearLayoutManager(this));
            recyclerView.setAdapter(recyclerAdapter);
        }
        catch(Exception e)
        {
            Toast.makeText(PropertyHome.this, "Error: "   e.toString(), Toast.LENGTH_LONG).show();
        }
    }
    ...
}