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Error while using recycler view inside a fragment

Time:10-20

I am trying to use a recycler view inside my dashboard fragment but the app crashes when I try to run the app and shows this error in logcat window -> Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference

This is my fragment code

package com.example.bookhub;
import android.content.Context;
import android.os.Bundle;

import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.Arrays;
import java.util.List;

public class Dashboard_Fragment extends Fragment {

RecyclerView Recycler;
RecyclerView.LayoutManager layoutManager;
Dashboard_Recycler_Adapter recyclerAdapter;
List<String> bookList = Arrays.asList(
        "P.S. I love You",
        "The Great Gatsby",
        "Anna Karenina",
        "Madame Bovary",
        "War & Peace",
        "Middlemarch",
        "The Adventures of Huckleberry Finn",
        "Moby-Dick",
        "The Lord of the Rings");

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

    Recycler = getActivity().findViewById(R.id.Recycler);

    layoutManager = new LinearLayoutManager(getActivity());

    recyclerAdapter = new Dashboard_Recycler_Adapter((Context) getActivity(),bookList);

    Recycler.setLayoutManager(layoutManager);
    Recycler.setAdapter(recyclerAdapter);

    return inflater.inflate(R.layout.fragment_dashboard, container, false);
}

}

This is the code for adapter

package com.example.bookhub;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;
import java.util.List;

public class Dashboard_Recycler_Adapter extends 
RecyclerView.Adapter<Dashboard_Recycler_Adapter.DashboardViewHolder>{

List<String> bookList;
public Dashboard_Recycler_Adapter(Context context, List<String> list)
{
    this.bookList = list;
}


@NonNull
@Override
public DashboardViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
{
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_view_single_row, parent, false);
    return new DashboardViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull DashboardViewHolder holder, int position)
{
    holder.textView.setText(bookList.get(position));
}

@Override
public int getItemCount()
{
    return bookList.size();
}

public static class DashboardViewHolder extends RecyclerView.ViewHolder
{
    TextView textView;
    public DashboardViewHolder(@NonNull View itemView) {
        super(itemView);

        textView = itemView.findViewById(R.id.txtRecyclerRowItem);
    }
}

}

This is the XML Code of the recycler view in the dashboard fragment

<?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="match_parent"
android:layout_height="match_parent"
tools:context=".Dashboard_Fragment">

<!-- TODO: Update blank fragment layout -->
<TextView
    android:id="@ id/textView2"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    android:text="@string/dashboard_fragment"
    android:textSize="20sp" />

<androidx.recyclerview.widget.RecyclerView
    android:id="@ id/Recycler"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="35dp"
    android:padding="10dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.088"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.075" />

</androidx.constraintlayout.widget.ConstraintLayout>

CodePudding user response:

You should inflate the view before to get its RecyclerView.

import java.util.Arrays;
import java.util.List;

public class Dashboard_Fragment extends Fragment {

    RecyclerView recycler;
    
    Dashboard_Recycler_Adapter recyclerAdapter;
    List<String> books= Arrays.asList(
        "P.S. I love You",
        "The Great Gatsby",
        "Anna Karenina",
        "Madame Bovary",
        "War & Peace",
        "Middlemarch",
        "The Adventures of Huckleberry Finn",
        "Moby-Dick",
        "The Lord of the Rings");

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_dashboard, container, false);

        recycler = view.findViewById(R.id.Recycler);

        recyclerAdapter = new Dashboard_Recycler_Adapter(requiredContext(), books);

        recycler.setLayoutManager(new LinearLayoutManager(requiredActivity()));
        recycler.setAdapter(recyclerAdapter);

        return view;
    }
}

Advices : you should name your classes in camel case format (DashboardFragment, DashboardRecyclerAdapter etc.). In fragments use resquiredContext and requiredActivity when you wants context or activity.

CodePudding user response:

Change this line

RecyclerView Recycler;

to this

RecyclerView recycler;

and also this line

Recycler = getActivity().findViewById(R.id.Recycler);

to this

recycler= getActivity().findViewById(R.id.Recycler);
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