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Android: Unable to pause activity : java.lang.NullPointerException: null object reference [duplicate]

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What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 3 years ago.
Everything works fine in my app but when I press the back button (I mean exit app) the app is crashing. And I don't know why? I tried a couple of solutions but nothing works. It's a sounds/ringtones application.
I am a newbie at Android and I need some advice like "delete this" / "add this"
Here my code
package com.app.trying;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Environment;
import android.support.design.widget.NavigationView;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.MenuItem;
import android.widget.Toast;
import com.app.trying.tabs.Tab3;
import com.app.trying.tabs.Tab1;
import com.app.trying.tabs.Tab2;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import java.io.File;
public class MainActivity extends AppCompatActivity {
public MediaPlayer mp;
DrawerLayout mDrawerLayout;
NavigationView mNavigationView;
FragmentManager mFragmentManager;
FragmentTransaction mFragmentTransaction;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Banner Ad
AdView mAdView = (AdView) findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder().build();
mAdView.loadAd(adRequest);
toolbarTabs();
sidebar();
externalStorageAccess();
}
// Creates sidebar and sets onClickListeners
public void sidebar(){
mNavigationView = (NavigationView) findViewById(R.id.navigationView);
mNavigationView.setItemIconTintList(null);
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
mDrawerLayout.closeDrawers();
switch (menuItem.getItemId()){
case R.id.sounds:
FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
xfragmentTransaction.replace(R.id.containerView,new TabFragment()).commit();
break;
case R.id.share:
Intent shareIntent = new Intent(Intent.ACTION_SEND);
shareIntent.setType("text/plain");
shareIntent.putExtra(Intent.EXTRA_SUBJECT, getText(R.string.app_name));
shareIntent.putExtra(Intent.EXTRA_TEXT, getText(R.string.share_text) + " " + getText(R.string.app_name) + "\n\n" + getText(R.string.playstore_link));
startActivity(Intent.createChooser(shareIntent, getText(R.string.share_via)));
break;
}
return false;
}
});
}
// Is listening which sound on Tab1 has been clicked
public void TabOneItemClicked(int position) {
cleanUpMediaPlayer();
mp=MediaPlayer.create(MainActivity.this, Tab1.soundfiles[position]);
mp.start();
}
// Is listening which sound on Tab2 has been clicked
public void TabTwoItemClicked(int position) {
cleanUpMediaPlayer();
mp=MediaPlayer.create(MainActivity.this, Tab2.soundfiles[position]);
mp.start();
}
// Is listening which sound on Tab3 has been clicked
public void TabThreeItemClicked ( int position){
cleanUpMediaPlayer();
mp=MediaPlayer.create(MainActivity.this, Tab3.soundfiles[position]);
mp.start();
}
// Cleans MediaPlayer
public void cleanUpMediaPlayer() {
if (mp != null) {
try {
mp.stop();
mp.release();
mp = null;
} catch (Exception e) {
e.printStackTrace();
Toast.makeText(MainActivity.this, "Error", Toast.LENGTH_LONG).show();
}
}
}
// Access external storage
public void externalStorageAccess(){
final File FILES_PATH = new File(Environment.getExternalStorageDirectory(), "Android/data/"+ getText(R.string.package_name) +"/files");
if (Environment.MEDIA_MOUNTED.equals(
Environment.getExternalStorageState())) {
if (!FILES_PATH.mkdirs()) {
Log.w("error", "Could not create " + FILES_PATH);
}
} else {
Toast.makeText(MainActivity.this, "Error", Toast.LENGTH_LONG).show();
finish();
}
}
// Creates toolbar Tabs
public void toolbarTabs(){
mFragmentManager = getSupportFragmentManager();
mFragmentTransaction = mFragmentManager.beginTransaction();
mFragmentTransaction.replace(R.id.containerView, new TabFragment()).commit();
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
android.support.v7.widget.Toolbar toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.toolbar);
ActionBarDrawerToggle mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, toolbar, R.string.app_name,
R.string.app_name);
mDrawerLayout.setDrawerListener(mDrawerToggle);
mDrawerToggle.syncState();
}
#Override
protected void onPause() {
super.onPause();
stopMediaPlayer();
}
public void stopMediaPlayer()
{
mp.stop();
}
}
And this is my error logs.
2019-05-09 19:13:22.296 704-704/? E/cnss-daemon: Invalid mac address: 0x555555f110M
2019-05-09 19:13:32.682 704-704/? E/cnss-daemon: Stale or unreachable neighbors, ndm state: 4
2019-05-09 19:13:39.537 443-2253/? E/ANDR-PERF-MPCTL: Invalid profile no. 0, total profiles 0 only
2019-05-09 19:13:40.333 24095-24175/? E/libEGL: validate_display:99 error 3008 (EGL_BAD_DISPLAY)
2019-05-09 19:13:43.035 443-2253/? E/ANDR-PERF-MPCTL: Invalid profile no. 0, total profiles 0 only
2019-05-09 19:13:43.116 24095-24095/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.app.trying, PID: 24095
java.lang.RuntimeException: Unable to pause activity {com.app.trying/com.app.trying.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.stop()' on a null object reference
at android.app.ActivityThread.performPauseActivityIfNeeded(ActivityThread.java:3735)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3701)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3675)
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3649)
at android.app.ActivityThread.-wrap16(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1487)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6111)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.stop()' on a null object reference
at com.app.trying.MainActivity.stopMediaPlayer(MainActivity.java:155)
at com.app.trying.MainActivity.onPause(MainActivity.java:150)
at android.app.Activity.performPause(Activity.java:6917)
at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1323)
at android.app.ActivityThread.performPauseActivityIfNeeded(ActivityThread.java:3724)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3701) 
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3675) 
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3649) 
at android.app.ActivityThread.-wrap16(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1487) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6111) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
2019-05-09 19:13:43.736 2484-2484/? E/Launcher3: Meminfo, NativeHeapAllocatedSize18887424
2019-05-09 19:13:43.736 2484-2484/? E/Launcher3: Meminfo, NativeHeapSize35651584
2019-05-09 19:13:43.736 2484-2484/? E/Launcher3: Meminfo, getNativeHeapFreeSize16764160
2019-05-09 19:13:51.682 704-704/? E/cnss-daemon: Stale or unreachable neighbors, ndm state: 4
How should I resolve this error? Any help would be great. Thanks.

Your MediaPlayer instance is null as shown in the stacktrace, so:
public void stopMediaPlayer()
{
if (mp != null) {
mp.stop();
}
}

It can happen that your MediaPlayer instance is never initialization. So you have to handle it.

MPAndroidChart keeps throwing null error

I'm just trying this library out to see if it fits my needs and so far I have not been able to get it to work. Here is the code
package com.example.user.bottomnavigationbar;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;
import com.github.mikephil.charting.charts.PieChart;
import com.github.mikephil.charting.data.PieData;
import com.github.mikephil.charting.data.PieDataSet;
import com.github.mikephil.charting.data.PieEntry;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
PieChart pc;
private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
= new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.navigation_home:
return true;
// case R.id.navigation_overview:
// Intent intentOverview = new Intent(MainActivity.this, activity_test.class);
// intentOverview.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
// MainActivity.this.finish();
// startActivity(intentOverview);
// return true;
case R.id.navigation_expenses:
return true;
case R.id.navigation_reminder:
return true;
case R.id.navigation_income:
return true;
case R.id.navigation_login:
Intent intentLogin = new Intent(MainActivity.this, LoginActivity.class);
intentLogin.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
MainActivity.this.finish();
startActivity(intentLogin);
return true;
}
return false;
}
};
#Override
protected void onCreate(Bundle savedInstanceState)
{
pc = findViewById(R.id.chart);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BottomNavigationView navigation = findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
ArrayList <PieEntry> pieData = new ArrayList<>();
pieData.add(new PieEntry(10));
pieData.add(new PieEntry(20));
pieData.add(new PieEntry(30));
PieDataSet dataSet = new PieDataSet(pieData, "Survey Results");
PieData data = new PieData(dataSet);
pc.setData(data);
}
public void onBackPressed()
{
new AlertDialog.Builder(this)
.setIcon(android.R.drawable.ic_dialog_alert)
.setTitle("Closing Activity")
.setMessage("Are you sure you want to close this activity?")
.setPositiveButton("Yes", new DialogInterface.OnClickListener()
{
#Override
public void onClick(DialogInterface dialog, int which) {
finish();
}
})
.setNegativeButton("No", null)
.show();
}
}
And here is the error I get
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.user.bottomnavigationbar, PID: 4172
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.bottomnavigationbar/com.example.user.bottomnavigationbar.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.github.mikephil.charting.charts.PieChart.setData(com.github.mikephil.charting.data.ChartData)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.github.mikephil.charting.charts.PieChart.setData(com.github.mikephil.charting.data.ChartData)' on a null object reference
at com.example.user.bottomnavigationbar.MainActivity.onCreate(MainActivity.java:78)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
at android.app.ActivityThread.access$800(ActivityThread.java:151) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5254) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
I've searched for a bit and all I've found was that for others, they did not initialize the object hence it throws this error. Now someone did mention that it is possible to create the chart in code and then add it to the activity as the documentation's Getting Started page suggests but I have been unable to get it working. So what gives?
P.S Left in the code for navigation as I'm not sure if it might be the cause of the issue

You are first finding the view and then providing the content view to your activity replace with this code
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pc = findViewById(R.id.chart);
BottomNavigationView navigation = findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
ArrayList <PieEntry> pieData = new ArrayList<>();
pieData.add(new PieEntry(10));
pieData.add(new PieEntry(20));
pieData.add(new PieEntry(30));
PieDataSet dataSet = new PieDataSet(pieData, "Survey Results");
PieData data = new PieData(dataSet);
pc.setData(data);
}

My App is crashing on startup and i have no clue why. Gradle build runs fine without any errors

I'm making an app that by now should save and then get the value of a numeric Edit Text. When i put to load data from string.xml it went fine, but when i switched to SharedPreferences it didn't even start. Any help finding the problem would be appreciated. BTW .java is below and i'm sure layout .xml is fine.
package programmingandroidapps.brightnesscustomizationapp;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import android.util.Log;
import android.content.SharedPreferences;
import android.content.Context;
public class MainActivity extends AppCompatActivity {
//Declarations
String brightnessValue;
int choice, brightnessValueInt;
final EditText mEditText1=(EditText)findViewById(R.id.editText1), mEditText2=(EditText)findViewById(R.id.editText2), mEditText3=(EditText)findViewById(R.id.editText3), mEditText4=(EditText)findViewById(R.id.editText4), mEditText5=(EditText)findViewById(R.id.editText5);
Button mButton1=(Button)findViewById(R.id.button1), mButton2=(Button)findViewById(R.id.button2), mButton3=(Button)findViewById(R.id.button3), mButton4=(Button)findViewById(R.id.button4), mButton5=(Button)findViewById(R.id.button5);
SharedPreferences storedBrightness1 = this.getSharedPreferences("brightv1", Context.MODE_PRIVATE), storedBrightness2 = this.getSharedPreferences("brightv2", Context.MODE_PRIVATE), storedBrightness3 = this.getSharedPreferences("brightv3", Context.MODE_PRIVATE), storedBrightness4 = this.getSharedPreferences("brightv4", Context.MODE_PRIVATE), storedBrightness5 = this.getSharedPreferences("brightv5", Context.MODE_PRIVATE);
SharedPreferences.Editor mEditor;
//
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Get saved brightness values from string.xml and set them to ediText1-5
brightnessValueInt = storedBrightness1.getInt("brightv1", 0);
brightnessIntToString();
printToEditText(1);
brightnessValueInt = storedBrightness2.getInt("brightv2", 0);
brightnessIntToString();
printToEditText(2);
brightnessValueInt = storedBrightness3.getInt("brightv3", 0);
brightnessIntToString();
printToEditText(3);
brightnessValueInt = storedBrightness4.getInt("brightv4", 0);
brightnessIntToString();
printToEditText(4);
brightnessValueInt = storedBrightness5.getInt("brightv5", 0);
brightnessIntToString();
printToEditText(5);
//
// On Click Button Listeners
mButton1.setOnClickListener(
new View.OnClickListener()
{
public void onClick(View view)
{
//Validate >=0 and <=100, paint #222222 if is valid, paint red if not
Log.v(brightnessValue, mEditText1.getText().toString());
mEditor = storedBrightness1.edit();
mEditor.putInt("brightv1", brightnessValueInt);
}
});
//
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void printToEditText(int choice)
{
if(choice==1)
{
mEditText1.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==2)
{
mEditText2.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==3)
{
mEditText3.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==4)
{
mEditText4.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else
{
mEditText5.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
}
public void brightnessIntToString()
{
brightnessValue=brightnessValueInt+"";
}
}
I believe this is the applications crash log. I'm new to Android so if it is not just say it, no need to get angry :P
05-01 13:24:53.061 1624-1624/programmingandroidapps.brightnesscustomizationapp D/dalvikvm: Not late-enabling CheckJNI (already on)
05-01 13:24:56.451 1624-1624/programmingandroidapps.brightnesscustomizationapp D/AndroidRuntime: Shutting down VM
05-01 13:24:56.451 1624-1624/programmingandroidapps.brightnesscustomizationapp W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xb3d11b20)
05-01 13:24:56.471 1624-1624/programmingandroidapps.brightnesscustomizationapp E/AndroidRuntime:
FATAL EXCEPTION: main
Process: programmingandroidapps.brightnesscustomizationapp, PID: 1624
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{programmingandroidapps.brightnesscustomizationapp/programmingandroidapps.brightnesscustomizationapp.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.app.Activity.findViewById(Activity.java:1884)
at programmingandroidapps.brightnesscustomizationapp.MainActivity.<init>(MainActivity.java:21)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1208)
at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) 
at android.app.ActivityThread.access$800(ActivityThread.java:135) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:136) 
at android.app.ActivityThread.main(ActivityThread.java:5001) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
at dalvik.system.NativeStart.main(Native Method) 

The problem is that you are calling findViewById and getSharedPreferences before layout has been applied and the activity (this) was initialized. You should put those method calls in onCreate after setContentView(R.layout.activity_main);.

Dejan is right about moving part of the code into the onCreate lifecycle method, specifically, your code should change to something like this:
package programmingandroidapps.brightnesscustomizationapp;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import android.util.Log;
import android.content.SharedPreferences;
import android.content.Context;
public class MainActivity extends AppCompatActivity {
//Declarations
String brightnessValue;
int choice, brightnessValueInt;
private EditText mEditText1, mEditText2, mEditText3, mEditText4, mEditText5;
private Button mButton1,mButton2, mButton3, mButton4, mButton5;
private SharedPreferences storedBrightness1, storedBrightness2, storedBrightness3,storedBrightness4,storedBrightness5;
private SharedPreferences.Editor mEditor;
//
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mButton1 =(Button)findViewById(R.id.button1);
mButton2=(Button)findViewById(R.id.button2);
mButton3=(Button)findViewById(R.id.button3);
mButton4=(Button)findViewById(R.id.button4);
mButton5=(Button)findViewById(R.id.button5);
mEditText1 =(EditText)findViewById(R.id.editText1);
mEditText2=(EditText)findViewById(R.id.editText2);
mEditText3=(EditText)findViewById(R.id.editText3);
mEditText4=(EditText)findViewById(R.id.editText4);
mEditText5=(EditText)findViewById(R.id.editText5);
//instead of doing this, I'd rather use "named" SharedPreferences - call it "brightness" and will carry the five values
//something like SharedPreferences brightnessPreferences = this.getSharedPreferences("brightness", Context.MODE_PRIVATE);
//I ma just adding this here because that's the way you have it
storedBrightness1 = this.getSharedPreferences("brightv1", Context.MODE_PRIVATE),
storedBrightness2 = this.getSharedPreferences("brightv2", Context.MODE_PRIVATE),
storedBrightness3 = this.getSharedPreferences("brightv3", Context.MODE_PRIVATE),
storedBrightness4 = this.getSharedPreferences("brightv4", Context.MODE_PRIVATE),
storedBrightness5 = this.getSharedPreferences("brightv5", Context.MODE_PRIVATE);
//Get saved brightness values from string.xml and set them to ediText1-5
brightnessValueInt = storedBrightness1.getInt("brightv1", 0);
brightnessIntToString();
printToEditText(1);
brightnessValueInt = storedBrightness2.getInt("brightv2", 0);
brightnessIntToString();
printToEditText(2);
brightnessValueInt = storedBrightness3.getInt("brightv3", 0);
brightnessIntToString();
printToEditText(3);
brightnessValueInt = storedBrightness4.getInt("brightv4", 0);
brightnessIntToString();
printToEditText(4);
brightnessValueInt = storedBrightness5.getInt("brightv5", 0);
brightnessIntToString();
printToEditText(5);
//
// On Click Button Listeners
mButton1.setOnClickListener(
new View.OnClickListener()
{
public void onClick(View view)
{
//Validate >=0 and <=100, paint #222222 if is valid, paint red if not
Log.v(brightnessValue, mEditText1.getText().toString());
mEditor = storedBrightness1.edit();
mEditor.putInt("brightv1", brightnessValueInt);
}
});
//
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void printToEditText(int choice)
{
if(choice==1)
{
mEditText1.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==2)
{
mEditText2.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==3)
{
mEditText3.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==4)
{
mEditText4.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else
{
mEditText5.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
}
public void brightnessIntToString()
{
brightnessValue=brightnessValueInt+"";
}
}

Android Drawer items not working

I have created a drawer menu in android studio and changed items of drawer. I want to start another activity or view another layout on item click. but i get the following error and application is stopped.
03-24 21:38:28.202 2227-10289/? D/GassUtils: Found app info for package com.example.imran.myapp:1. Hash: 6b9333e031907d7a6a6c12cd9fdfa0d23bd13ee0f40c9617ddd005dc358321b0
03-24 21:38:28.202 2227-10289/? D/k: Found info for package com.example.imran.myapp in db.
03-24 21:38:38.722 1035-1167/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:38.782 9789-9789/? I/Timeline: Timeline: Activity_launch_request id:com.example.imran.myapp time:121627337
03-24 21:38:38.802 1035-1853/? W/ActivityManager: NORMAL SET : srcAppInfo.processName = com.example.imran.myapp, destAppInfo.processName = com.example.imran.myapp
03-24 21:38:38.802 1035-1853/? W/ActivityManager: startActivity called from finishing ActivityRecord{28b176ac u0 com.example.imran.myapp/.MainActivity t2394 f}; forcing Intent.FLAG_ACTIVITY_NEW_TASK for: Intent { cmp=com.example.imran.myapp/.Home (has extras) }
03-24 21:38:38.802 1035-1853/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:39.402 1035-1532/? I/WindowManager: Switching to real app window: Window{11c67d3b u0 com.example.imran.myapp/com.example.imran.myapp.Home}
03-24 21:38:39.622 1035-1069/? I/Timeline: Timeline: Activity_windows_visible id: ActivityRecord{dca1b0 u0 com.example.imran.myapp/.Home t2396} time:121628177
03-24 21:38:58.462 9789-9789/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.imran.myapp, PID: 9789
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.widget.DrawerLayout.closeDrawer(int)' on a null object reference
at com.example.imran.myapp.Home.onNavigationItemSelected(Home.java:120)
at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:146)
at android.support.v7.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.internal.view.menu.SubMenuBuilder.dispatchMenuItemSelected(SubMenuBuilder.java:84)
at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:153)
at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.design.internal.NavigationMenuPresenter.onItemClick(NavigationMenuPresenter.java:196)
at android.widget.AdapterView.performItemClick(AdapterView.java:334)
at android.widget.AbsListView.performItemClick(AbsListView.java:1536)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3683)
at android.widget.AbsListView$3.run(AbsListView.java:5604)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6145)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
03-24 21:38:58.462 1035-1514/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:58.462 1035-1514/? W/ActivityManager: Force finishing activity com.example.imran.myapp/.Home
03-24 21:38:58.462 1035-1514/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:58.542 1035-1035/? D/CrashAnrDetector: processName: com.example.imran.myapp
03-24 21:38:58.542 1035-1035/? D/CrashAnrDetector: broadcastEvent : com.example.imran.myapp data_app_crash
03-24 21:38:58.992 1035-1062/? W/ActivityManager: Activity pause timeout for ActivityRecord{dca1b0 u0 com.example.imran.myapp/.Home t2396 f}
Java files:
Home.java
package com.example.imran.myapp;
import android.app.ProgressDialog;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.TextView;
public class Home extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
Button logout = (Button) findViewById(R.id.logout_button);
TextView text1 = (TextView) findViewById(R.id.result_sms);
final UserLocalStore loginuser = new UserLocalStore(getApplicationContext());
SharedPreferences mPrefs = getSharedPreferences("userDetails",0);
String str1=(mPrefs.getString("fullname","Default_Value"));
String email = loginuser.getLoggedInUser().email;
text1.setText("Welcome "+str1+"- Your email: "+email);
logout.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
loginuser.clearUserData();
//startActivity(new Intent(getApplicationContext(), MainActivity.class));
finish();
startActivity(new Intent(getApplicationContext(), MainActivity.class));
//setContentView(R.layout.activity_main);
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
#Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.home, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
#SuppressWarnings("StatementWithEmptyBody")
#Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_photos) {
// Handle the camera action
//setContentView(R.layout.myaccount);
} else if (id == R.id.nav_myaccount) {
setContentView(R.layout.activity_myaccount2);
//
} else if (id == R.id.nav_logout) {
UserLocalStore loginuser = new UserLocalStore(this);
loginuser.clearUserData();
finish();
startActivity(new Intent(getApplicationContext(), MainActivity.class));
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
In the last part of home.java when i add setContentView(R.layout.activity_myaccount2);
then the app crashes.

The problem here is a Null Pointer Exception when calling drawer.closeDrawer(); and as you've stated this happens after setContentView(R.layout.activity_myaccount2); is called.
By using setContentView, you're replacing your whole layout with another one, and it seems in this case like you're replacing your layout that contains R.id.drawer_layout with another one that doesn't contain it. The null pointer exception then happens when you try to use findViewById and closeDrawer, when the layout containing the drawer isn't there anymore, it's been replaced with another using setContentView.
To fix this you may need to rethink how you are structuring your app and displaying different content. As a starting point, I'd suggest looking up examples using an Activity which contains your drawer and Fragments to show the different pieces of content. The Activity and drawer are always there, only the fragments change, like this tutorial.

I have simple android App in android studio and it does not work

package viewbrosers.mehdi.home.mytestappviewbrowser;
import android.app.Activity;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
import java.util.Random;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button getAnswer = (Button) findViewById(R.id.getAnswerButton);
getAnswer.setOnClickListener(getAnswerListener);
}
private View.OnClickListener getAnswerListener = new View.OnClickListener() {
#Override
public void onClick(View v) {
Random randomnum = new Random();
int numToast = randomnum.nextInt(19);
numToast++;
CharSequence text = "";
switch (numToast) {
case 1:
text = getString(R.string.answer1);
break;
case 2:
text = getString(R.string.answer2);
break;
case 3:
text = getString(R.string.answer3);
break;
case 4:
text = getString(R.string.answer4);
break;
case 5:
text = getString(R.string.answer5);
break;
case 6:
text = getString(R.string.answer6);
break;
case 7:
text = getString(R.string.answer7);
break;
}
Context context = getApplicationContext();
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
};
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
My error is:
Unfortunately Application has stopped and 06-05
11:31:44.131 13711-13711/? I/art﹕ Not late-enabling -Xcheck:jni
(already on) 06-05 11:31:44.208 13711-13711/? D/AndroidRuntime﹕
Shutting down VM 06-05 11:31:44.208 13711-13711/? E/AndroidRuntime﹕
FATAL EXCEPTION: main
Process: viewbrosers.mehdi.home.mytestappviewbrowser, PID: 13711
java.lang.RuntimeException: Unable to start activity ComponentInfo{viewbrosers.mehdi.home.mytestappviewbrowser/viewbrosers.mehdi.home.mytestappviewbrowser.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method
'boolean java.lang.String.equals(java.lang.Object)' on a null object
reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on
a null object reference
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:715)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:378)
at android.app.Activity.setContentView(Activity.java:2145)
at viewbrosers.mehdi.home.mytestappviewbrowser.MainActivity.onCreate(MainActivity.java:23)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 06-05
11:31:44.218 13711-13718/? I/art﹕ Debugger is no longer active 06-05
11:32:28.690 13711-13718/viewbrosers.mehdi.home.mytestappviewbrowser
W/art﹕ Suspending all threads took: 12.748ms

Move the creation and initialization of your text variable outside of the onClick() method. Try the following code.
public class MainActivity extends Activity {
CharSequence text;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
text = "";
Button getAnswer = (Button) findViewById(R.id.getAnswerButton);
getAnswer.setOnClickListener(getAnswerListener);
}
private View.OnClickListener getAnswerListener = new View.OnClickListener() {
#Override
public void onClick(View v) {
Random randomnum = new Random();
int numToast = randomnum.nextInt(19);
numToast++;
switch (numToast) {
case 1:
text = getString(R.string.answer1);
break;
case 2:
text = getString(R.string.answer2);
break;
case 3:
text = getString(R.string.answer3);
break;
case 4:
text = getString(R.string.answer4);
break;
case 5:
text = getString(R.string.answer5);
break;
case 6:
text = getString(R.string.answer6);
break;
case 7:
text = getString(R.string.answer7);
break;
}
Context context = getApplicationContext();
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
};
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

You are somewhere using equals function on string which is null.
Look at exception: 'boolean java.lang.String.equals(java.lang.Object)' on a null object
reference

Try it, may be like this.
public class MainActivity extends Activity implements OnClickListener
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button getAnswer = (Button) findViewById(R.id.getAnswerButton);
getAnswer.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch (v.getId())
{
case R.id.getAnswerButton:
//Your code
break;
}
}
}