Getting NullPointerException at NavigationView

Question

I'm trying to make a Drawer Menu but i'm having NullPointer, but i think everything is corect.

I'll post all my code here:

package wagner.com.meuartesanato.home;

import android.content.Intent;
import android.net.Uri;
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import wagner.com.meuartesanato.R;

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    private DrawerLayout drawer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        showHome(null);

        TextView textMenu = (TextView) findViewById(R.id.text_menu);
        TextView textHome = (TextView) findViewById(R.id.text_home);
        TextView textSimulation = (TextView) findViewById(R.id.text_simulation);

        drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        loadDrawer();
    }

    public void showMenu(View v){
        //drawer.openDrawer(GravityCompat.END);
    }

    public void showHome(View v){
        //loadFragment(Home1Fragment.class);
    }

    public void showSimulation(View v){
        Toast.makeText(this,"Mostrar simulação",Toast.LENGTH_SHORT).show();
    }

    private void loadDrawer(){

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        View view = navigationView.getHeaderView(0);


        Button about = (Button)view.findViewById(R.id.button_about);
        Button howToUse = (Button)view.findViewById(R.id.button_how_to_use);
        Button addAccount = (Button)view.findViewById(R.id.button_add_account);
        Button changeRegister = (Button)view.findViewById(R.id.button_change_register);
        Button changePassword = (Button)view.findViewById(R.id.button_change_password);
        Button help = (Button)view.findViewById(R.id.button_help);
        Button exit = (Button)view.findViewById(R.id.button_exit);

        about.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //Mostra tela sobre o app
                //loadFragment(SobreFragment.class);
                drawer.closeDrawer(GravityCompat.END);
            }
        });

        howToUse.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this,"Mostrar como usar",Toast.LENGTH_SHORT).show();
                drawer.closeDrawer(GravityCompat.END);
            }
        });


        addAccount.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this,"Mostrar algo",Toast.LENGTH_SHORT).show();
                drawer.closeDrawer(GravityCompat.END);

            }
        });


        changeRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this,"Alterar cadastro",Toast.LENGTH_SHORT).show();
                drawer.closeDrawer(GravityCompat.END);
            }
        });


        changePassword.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this,"Alterar cadastro",Toast.LENGTH_SHORT).show();
                drawer.closeDrawer(GravityCompat.END);
            }
        });


        help.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this,"Help",Toast.LENGTH_SHORT).show();
                drawer.closeDrawer(GravityCompat.END);
            }
        });


        exit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //fecha a activity, voltando pra tela de login
                finish();

            }
        });

    }

    private void loadFragment(Class fragmentClass){
        try {
            Fragment fragment = (Fragment) fragmentClass.newInstance();
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.fragment_holder, fragment).commit();
        }catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        drawer.closeDrawer(GravityCompat.END);
        return false;
    }

    @Override
    public void onBackPressed() {
        if (drawer.isDrawerOpen(GravityCompat.END)) {
            drawer.closeDrawer(GravityCompat.END);
        } else {
            drawer.openDrawer(GravityCompat.END);
        }
    }
}

And my xml files:

activity_home.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.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:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <include
        layout="@layout/activity_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="end"
        app:headerLayout="@layout/nav_header_main"
        android:fitsSystemWindows="true"
        android:background="@color/colorWhite"/>

</android.support.v4.widget.DrawerLayout>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="10dp"
    android:background="@drawable/degrade"
    tools:context="wagner.com.meuartesanato.home.MainActivity">

    <LinearLayout
        android:baselineAligned="false"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/top_bar">

        <LinearLayout
            android:onClick="showMenu"
            android:layout_width="0dp"
            android:layout_weight="3"
            android:gravity="center_horizontal"
            android:orientation="vertical"
            android:layout_gravity="center_vertical"
            android:layout_height="wrap_content">
            <ImageView
                android:layout_width="60dp"
                android:layout_height="60dp"
                android:src="@mipmap/menu"/>
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:id="@+id/text_menu"
                android:layout_marginTop="5dp"
                android:textSize="12sp"
                android:textColor="#FFF"
                android:text="Menu"/>
        </LinearLayout>

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="3"
            android:onClick="showHome"
            android:gravity="center_horizontal"
            android:orientation="vertical"
            android:layout_gravity="center_vertical">
            <ImageView
                android:layout_width="60dp"
                android:layout_height="60dp"
                android:src="@mipmap/home"/>
            <TextView
                android:id="@+id/text_home"
                android:layout_marginTop="5dp"
                android:textSize="12sp"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textColor="#FFF"
                android:text="Home"
                />
        </LinearLayout>

        <LinearLayout
            android:onClick="showSimulation"
            android:layout_width="0dp"
            android:layout_weight="3"
            android:gravity="center_horizontal"
            android:orientation="vertical"
            android:layout_gravity="center_vertical"
            android:layout_height="wrap_content">
            <ImageView
                android:layout_width="60dp"
                android:layout_height="60dp"
                android:src="@mipmap/simulacao"
                />
            <TextView
                android:id="@+id/text_simulation"
                android:layout_marginTop="5dp"
                android:layout_width="wrap_content"
                android:textSize="12sp"
                android:layout_height="wrap_content"
                android:textColor="#FFF"
                android:text="Simulação"
                />
        </LinearLayout>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:layout_below="@id/top_bar">
        <View
            android:layout_width="match_parent"
            android:layout_height="10dp"
            android:background="@drawable/shadow"/>

        <FrameLayout
            android:id="@+id/fragment_holder"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#FFF"
            android:layout_marginBottom="@dimen/activity_vertical_margin">
        </FrameLayout>

    </LinearLayout>
</RelativeLayout>

nav_header_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:background="#FFF"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal">

    <ImageView
        android:id="@+id/drawer_avatar"
        android:layout_marginTop="20dp"
        android:layout_width="115dp"
        android:layout_height="115dp" />
    <TextView
        android:id="@+id/full_name"
        android:layout_width="180dp"
        android:gravity="center"
        android:textColor="@color/colorDarkGray"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:layout_marginBottom="20dp"
        android:layout_marginTop="10dp"
        />

    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorLightGray"
        android:text="Sobre o App"
        android:id="@+id/button_about"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />


    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorWhite"
        android:text="Como usar o App"
        android:id="@+id/button_how_to_use"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />


    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorLightGray"
        android:text="Adicionar Conta Bancaria?"
        android:id="@+id/button_add_account"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />


    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorWhite"
        android:text="Alterar Cadastro?"
        android:id="@+id/button_change_register"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />

    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorLightGray"
        android:text="Alterar Senha?"
        android:id="@+id/button_change_password"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />



    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorWhite"
        android:text="Ajuda"
        android:id="@+id/button_help"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />
    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorLightGray"
        android:text="Sair"
        android:id="@+id/button_exit"
        android:textColor="@color/colorPurple"
        android:textSize="@dimen/normal_text"
        android:textAllCaps="false"
        />

    <TextView
        android:layout_marginTop="50dp"
        android:layout_marginBottom="20dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Copyright"
        android:textColor="@color/colorGray"
        />

</LinearLayout>

The error log is:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: wagner.com.meuartesanato, PID: 9112
    java.lang.RuntimeException: Unable to start activity ComponentInfo{wagner.com.meuartesanato/wagner.com.meuartesanato.home.MainActivity}:
    java.lang.NullPointerException: Attempt to invoke virtual method 'void
    android.support.design.widget.NavigationView.setNavigationItemSelectedListener(android.support.design.widget.NavigationView$OnNavigationItemSelectedListener)'
    on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
    at android.app.ActivityThread.-wrap11(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
    android.support.design.widget.NavigationView.setNavigationItemSelectedListener(android.support.design.widget.NavigationView$OnNavigationItemSelectedListener)'
    on a null object reference
    at wagner.com.meuartesanato.home.MainActivity.loadDrawer(MainActivity.java:59)
    at wagner.com.meuartesanato.home.MainActivity.onCreate(MainActivity.java:41)
    at android.app.Activity.performCreate(Activity.java:6237)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
    at android.app.ActivityThread.-wrap11(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:148) 
    at android.app.ActivityThread.main(ActivityThread.java:5417) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

I really don't know why i'm getting null pointer exception.

Thanks, for the answers!

Answer 1

The stack trace clearly says what is missing. You could have actually found out the programming error by carefully reviewing your code. Anyways modify the following line in your onCreate method. You were inflating the wrong layout

What it is now - setContentView(R.layout.activity_main);

What you should change it to - setContentView(R.layout.activity_home);