Getting error NullPointerException when using DrawerLayout in Android Studio-CodePudding

Getting a NullPointerException Error when trying to run my app, I will link code and Logcat error below, help would be greatly appreciated.

In my XML class with the DrawerLayout I have the ID for the drawer set to drawer_layout (renamed using android:id).

Logcat Error

2022-11-23 01:35:49.526 4976-4976/com.example.appdev2finalproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.appdev2finalproject, PID: 4976
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.appdev2finalproject/com.example.appdev2finalproject.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.drawerlayout.widget.DrawerLayout.addDrawerListener(androidx.drawerlayout.widget.DrawerLayout$DrawerListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.drawerlayout.widget.DrawerLayout.addDrawerListener(androidx.drawerlayout.widget.DrawerLayout$DrawerListener)' on a null object reference
    at com.example.appdev2finalproject.MainActivity.onCreate(MainActivity.java:21)
    at android.app.Activity.performCreate(Activity.java:7994)
    at android.app.Activity.performCreate(Activity.java:7978)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)

Code From Main

package com.example.appdev2finalproject;

import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.drawerlayout.widget.DrawerLayout;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
    DrawerLayout drawerLayout;
    ActionBarDrawerToggle actionBarDrawerToggle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        drawerLayout = findViewById(R.id.drawer_layout);
        actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.nav_open,
                R.string.nav_close);

        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    }
}

Edit: Adding Activity Main Code

<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout 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:id="@ id/drawer_layout"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.google.android.material.navigation.NavigationView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:menu="@menu/navigation_menu"/>

</androidx.drawerlayout.widget.DrawerLayout>

CodePudding user response：

I can't see any import statment of the resource file (i.e R.layout.file_name). It seems like you are importing your layout file from the wrong directory. It should be from com.example.appdev2finalproject.R. Put this import statement and your code should work fine then.

CodePudding user response：

Error found; I had forgotten to change the layout.activity_main toactivity_dashboard after creating new file to hold the Drawer Layout