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

Question

i am getting this NullPointerException Error in Java trying to run my app in android Studio. Below is my JavaFile

package com.example.app;

import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.fragment.app.Fragment;

import android.Manifest;
import android.content.SharedPreferences;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;


import com.example.app.AboutusFragment;
import com.example.app.AddProductFragment;
import com.example.app.AllProductsFragment;
import com.example.app.CartFragment;
import com.example.app.CategoryFragment;
import com.example.app.CatlistFragment;
import com.example.app.ChangePwdFragment;
import com.example.app.ContactusFragment;
import com.example.app.HomeFragment;
import com.example.app.LoginFragment;
import com.example.app.MediMartDbHelper;
import com.example.app.MediMartUtils;
import com.example.app.OrderHistoryFragment;
import com.example.app.OrdersFragment;
import com.example.app.R;
import com.example.app.RegisterFragment;
import com.google.android.material.navigation.NavigationView;
import com.google.android.material.snackbar.BaseTransientBottomBar;
import com.google.android.material.snackbar.Snackbar;

import java.util.List;

public class HomeActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    private DrawerLayout dlayout;
    private NavigationView nav;
    private ActionBarDrawerToggle drawerToggle;
    private Toolbar toolbar;
    private SharedPreferences sp;
    private MediMartDbHelper db;
    private TextView tv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        init();
        drawerToggle=new ActionBarDrawerToggle(this.getParent(),dlayout,toolbar,R.string.on,R.string.Off);
        dlayout.addDrawerListener(drawerToggle);
        drawerToggle.syncState();
        nav.setNavigationItemSelectedListener(this);
        permissions();
        MediMartUtils.loadFragment(this,new CategoryFragment());
        loadmenu();
    }

    public void init(){
        dlayout=findViewById(R.id.dlayout);
        nav= findViewById(R.id.nav_view);
        toolbar= findViewById(R.id.toolbar);
        tv= nav.getHeaderView(0).findViewById(R.id.tvusername);
        sp=getSharedPreferences("users",MODE_PRIVATE);
        db=new MediMartDbHelper(this);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("My Shop");
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.search_menu,menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        if(item.getItemId()==R.id.mcart){
            String user=sp.getString("userid","guest");
            if(user.equals("guest")) {
                MediMartUtils.loadFragment(this, new LoginFragment());
                Snackbar.make(getCurrentFocus(),"Please Login First",BaseTransientBottomBar.LENGTH_LONG).show();
            }else{
                MediMartUtils.loadFragment(this, new CartFragment());
            }
        }
        return super.onOptionsItemSelected(item);
    }

    public void loadmenu(){
        String user=sp.getString("userid","guest");
        Menu menu=nav.getMenu();
        switch(user) {
            case "guest":
                Log.d("Nauman", " i am in loadmenu: " + user);
                menu.setGroupVisible(R.id.gadmin, false);
                menu.setGroupVisible(R.id.guser, false);
                menu.setGroupVisible(R.id.gcustomer, false);
                tv.setText("Welcome Guest");
                break;
            case "admin":
                Log.d("Nauman", " i am in loadmenu: " + user);
                menu.setGroupVisible(R.id.gadmin, true);
                menu.setGroupVisible(R.id.guser, true);
                menu.setGroupVisible(R.id.gcustomer, false);
                tv.setText("Welcome Administrator");
                break;
            default:
                Log.d("Nauman", " i am in loadmenu: " + user);
                menu.setGroupVisible(R.id.guser, true);
                menu.setGroupVisible(R.id.gcustomer, true);
                menu.setGroupVisible(R.id.gadmin, false);
                Cursor c=db.findcustomer(user);
                c.moveToNext();
                tv.setText("Welcome "+c.getString(1));
                break;
        }
    }

    private void permissions(){
        if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.M){
            if(checkSelfPermission(Manifest.permission.CALL_PHONE)!= PackageManager.PERMISSION_GRANTED){
                requestPermissions(new String[]{Manifest.permission.CALL_PHONE},100);
            }
            if(checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
                requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},200);
            }
        }
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Fragment f=null;
        switch (item.getItemId()){
            case R.id.mhome:
                f=new HomeFragment();
                break;
            case R.id.mcat:
                f=new CatlistFragment();
                break;
            case R.id.mnoti:
                f=new OrderHistoryFragment();
                break;
            case R.id.mproducts:
                f=new CategoryFragment();
                break;
            case R.id.morders:
                f=new OrdersFragment();
                break;
            case R.id.mchangepwd:
                f=new ChangePwdFragment();
                break;
            case  R.id.maddpro:
                f=new AddProductFragment();
                break;
            case R.id.mshowall:
                f=new AllProductsFragment();
                break;
            case R.id.mlogout:
                SharedPreferences.Editor edit=sp.edit();
                edit.remove("userid");
                edit.remove("role");
                edit.commit();
                f=new CategoryFragment();
                Toast.makeText(this, "Sign out successfully..", Toast.LENGTH_SHORT).show();
                dlayout.closeDrawer(GravityCompat.START);
                return MediMartUtils.loadwithoutHistoryFragment(this,f);
            case  R.id.mcart:
                f=new CartFragment();
                break;
        }
        dlayout.closeDrawer(GravityCompat.START);
        return MediMartUtils.loadFragment(this,f);
    }

    @Override
    public void onBackPressed() {

        if(dlayout.isDrawerOpen(GravityCompat.START)){
            dlayout.closeDrawer(GravityCompat.START);
        }
        if(getSupportFragmentManager().getBackStackEntryCount()==0) {
            super.onBackPressed();
        }else{
            getSupportFragmentManager().popBackStack();
        }
    }

    public void login(View view) {
        MediMartUtils.loadFragment(this,new LoginFragment());
    }

    public void register(View view) {
        MediMartUtils.loadFragment(this,new RegisterFragment());
    }

    public void contactus(View view) {
        MediMartUtils.loadFragment(this,new ContactusFragment());
    }

    public void aboutus(View view) {
        MediMartUtils.loadFragment(this,new AboutusFragment());
    }

}

Here is my activity home layout file:

<?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.come/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start"
    tools:context=".MainActivity"
    android:id="@+id/dlayout">

    <include
        layout="@layout/main_content"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        />
    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/drawer_header"
        app:menu="@menu/drawer_menu"
    />

</androidx.drawerlayout.widget.DrawerLayout>

And here, where the id tvusername is assigned

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="220dp"
    android:background="#ffffff"
    android:layout_gravity="top"
    android:orientation="vertical"
    android:padding="10dp">

    <ImageView
        android:layout_width="150dp"
        android:layout_height="100dp"
        android:id="@+id/imageView14"
        app:srcCompat="@drawable/grocerrylogo"/>

        <TextView
            android:id="@+id/textView28"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="4dp"
            android:text="Shopify Cart"
            android:textColor="#8F10a5"
            android:textSize="25dp"/>

        <TextView
            android:id="@+id/tvusername"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="8dp"
            android:text="Welcome Guest"
            android:textColor="#640873"
            android:textSize="18dp"
            android:textStyle="bold"/>



</LinearLayout>

I have seen plenty of similiar post but and i tried to learn from them but it doesnt resonate within me. I truly do not understand why this error is thrown in line 75 which is this one:

tv= nav.getHeaderView(0).findViewById(R.id.tvusername);

And Line 61 which is this one: (probably because the error first comes from within the method)

init();

I can imagine that the error is pretty obvious and im just unable to see it:D Thanks alot!

If i have to provide any more information please let me know, this is my first posts on here.

I am trying to assign a ressource id to TextView tv; And i am getting the error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
                                                                                                        at com.example.app.HomeActivity.init(HomeActivity.java:75)
                                                                                                        at com.example.app.HomeActivity.onCreate(HomeActivity.java:61)

I am not sure why its not working and where the error seems to be

Answer 1

change your code like as follow

 tv = nav.findViewById(R.id.tvusername);

Please accept this answer if it solved your problem or was the most helpful in finding your solution