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Android chat app keeps on crashing when I run it

I have just begun writing some code for my Chat app after days of planning but the problem is that keeps on crashing right after the Gradle Build has finished and the app is installed on my device. I have created a button that is expected to open a new activity but instead of doing so it crashes. Everything works before I have written any code, the app opens and logcat doesn't show any errors. Here is the error:
2022-08-10 19:26:48.372 15348-15348/? E/e.myapplicatio: Unknown bits set in runtime_flags: 0x40000000
2022-08-10 19:26:48.391 15348-15348/? E/RefClass: java.lang.reflect.InvocationTargetException
2022-08-10 19:26:48.474 15348-15348/com.example.myapplication E/Perf: perftest packageName : com.example.myapplication App is allowed to use Hide APIs
2022-08-10 19:26:48.515 15348-15374/com.example.myapplication E/libEGL: Invalid file path for libcolorx-loader.so
2022-08-10 19:26:48.528 15348-15348/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 15348
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3628)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3887)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2317)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:263)
at android.app.ActivityThread.main(ActivityThread.java:8292)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:183)
at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174)
at android.content.Context.obtainStyledAttributes(Context.java:744)
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:848)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:815)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:640)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:259)
at com.example.myapplication.MainActivity.<init>(MainActivity.java:12)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1254)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3616)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3887) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2317) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:263) 
at android.app.ActivityThread.main(ActivityThread.java:8292) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006) 
I tried following some other suggestions but they didn't work. Here's the snippet of my code:
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
public Button signUp = findViewById(R.id.signUpBtn);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
signUp.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
openActivity();
}
});
}
public void openActivity(){
Intent intent = new Intent(this, LoginActivity.class);
startActivity(intent);
}
}

You can not use findViewById() outside of onCreate() like this and if you really wanna do that, do it by creating a new method for setting up IDs and then add that method in onCreate().
this code will do the work now:
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
public Button signUp;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
signUp = findViewById(R.id.signUpBtn);
signUp.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
openActivity();
}
});
}
public void openActivity(){
Intent intent = new Intent(this, LoginActivity.class);
startActivity(intent);
}
}

Android java won't run [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed last year.
I'm studying Android java, and I have this error and can't run it.
Could you help me fixing this error? What is the problem?
Is it related to the error that I can't make a onClickListener() lambda expression? It gives me error and I can't import. So I tried making new View.OnclickListener() and its color is grey.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 9974
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3635)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7839)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.myapplication.MainActivity.onCreate(MainActivity.java:31)
at android.app.Activity.performCreate(Activity.java:8051)
at android.app.Activity.performCreate(Activity.java:8031)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1329)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3608)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loopOnce(Looper.java:201) 
at android.os.Looper.loop(Looper.java:288) 
at android.app.ActivityThread.main(ActivityThread.java:7839) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) 
I/Process: Sending signal. PID: 9974 SIG: 9
And this is my mainActivity.
package com.example.myapplication;
import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
RadioGroup radioGroup;
TextView txtViewResults;
EditText editTextInputWt;
Button btnConvertWt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayShowHomeEnabled(true);
actionBar.setDisplayUseLogoEnabled(true);
actionBar.setLogo(R.mipmap.ic_launcher_weight_round);
actionBar.setTitle(R.string.txtTitle);
btnConvertWt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (radioGroup.getCheckedRadioButtonId() == -1){
Toast.makeText(MainActivity.this, "Please select conversion type", Toast.LENGTH_SHORT).show();
} else if (editTextInputWt.getText().toString().isEmpty()){
Toast.makeText(MainActivity.this, "Please select baggage weight", Toast.LENGTH_SHORT).show();
} else {
double inputWt, outputWt;
try{
inputWt = Double.parseDouble(editTextInputWt.getText().toString());
if (inputWt<0){
Toast.makeText(MainActivity.this, "Baggage weight can't be negative.", Toast.LENGTH_SHORT).show();
} else if (radioGroup.getCheckedRadioButtonId() == R.id.radBtnKgsToLbs){
if (inputWt > 500){
Toast.makeText(MainActivity.this, "Input bg wt can't be greater than 500Kilos", Toast.LENGTH_SHORT).show();
} else {
outputWt = inputWt*2.2;
txtViewResults.setText(String.format("Converted wt: %.2f Lbs", outputWt));
}
} else if (radioGroup.getCheckedRadioButtonId() == R.id.radBtnLbsToKgs){
if (inputWt > 1000){
Toast.makeText(MainActivity.this, "Input bg wt can't be greater than 1000 pounds", Toast.LENGTH_SHORT).show();
} else {
outputWt = inputWt/2.2;
txtViewResults.setText(String.format("Converted wt: %.2f Kgs", outputWt));
}
}
} catch (Exception ex){
ex.printStackTrace();
}
}
}
});
}
}

This is due to you haven't initialised your views and as of this stage they are null and you can't invoke method on null object in java which you can see in your error.
so for this you have to initalise your variable you can do like following
findViewById()
View Binding
Data Binding
Creating view programmatically
as you have used layout file you can do findViewById() as following
public class MainActivity extends AppCompatActivity {
RadioGroup radioGroup;
TextView txtViewResults;
EditText editTextInputWt;
Button btnConvertWt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
....
radioGroup = findViewById(R.id.my_radio_group);
btnConvertWt = findViewById(R.id.my_button); // the id's are same as defined in your layout file
....
btnConvertWt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
....
}
});
}
}

Nullable problem with Intents with extras

I am learning how to develop for Android (and development in general). I am trying to create a Quiz App, so I can learn the basics.
While trying to use an Intent to go to another class with an extra variable on it, I found this problem (which I think is pretty usual): My app crashes when I go to the next Activity.
This is the code in the activity that gets the username ("usuario and nomeUsuario"):
package com.isa56.quiz2;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
public class HomeActivity extends AppCompatActivity {
public EditText usuario;
public EditText senha;
public Button botaoLogin;
public String nomeUsuario;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
botaoLogin = findViewById(R.id.botaoLogin);
senha = findViewById(R.id.senha);
usuario = findViewById(R.id.usuario);
nomeUsuario = usuario.getText().toString();
Log.d("nome de usuario", nomeUsuario);
botaoLogin.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
Intent i = new Intent(HomeActivity.this, FirstQuestionActivity.class);
i.putExtra("nome", nomeUsuario);
startActivity(i);
}});
}
}
And this is the code on the SecondQuestionActivity:
package com.isa56.quiz2;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class FirstQuestionActivity extends AppCompatActivity {
public Button prox1;
public Button respUm1;
public Button respUm2;
public TextView texto1;
public int pontuacao = 0;
Intent i = getIntent();
String nome = i.getStringExtra("nome");
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_firstquestion);
prox1 = findViewById(R.id.prox1);
respUm1 = findViewById(R.id.botao1a);
respUm2 = findViewById(R.id.botao1b);
texto1 = findViewById(R.id.texto1);
respUm1.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
texto1.setText("Resposta errada!");
respUm1.setEnabled(false);
respUm2.setEnabled(false);
prox1.setEnabled(true);
}});
respUm2.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
texto1.setText("Resposta certa!");
respUm2.setEnabled(false);
respUm1.setEnabled(false);
pontuacao += 1;
prox1.setEnabled(true);
}});
prox1.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
Intent i = new Intent(FirstQuestionActivity.this, SecondQuestionActivity.class);
i.putExtra("pontos", pontuacao);
i.putExtra("nome", nome);
startActivity(i);
}
});
}
}
What is wrong with it? How can I prevent it?
Thank you!
P.S.: I am not used to forum or development in general, so I might have done this wrongly. I'm sorry.
Edit: Also, if anyone wanna take a look at the whole project, it's here.
Edit2: This is the Logcat output:
2020-11-13 21:05:18.531 7517-7517/com.isa56.quiz2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.isa56.quiz2, PID: 7517
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.isa56.quiz2/com.isa56.quiz2.FirstQuestionActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Intent.getStringExtra(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3365)
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 'java.lang.String android.content.Intent.getStringExtra(java.lang.String)' on a null object reference
at com.isa56.quiz2.FirstQuestionActivity.<init>(FirstQuestionActivity.java:18)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1253)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3353)
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) 

Keep these lines inside onCreate() method.
Intent i = getIntent();
String nome = i.getStringExtra("nome");

I run my android app and no app launches and gives errors in the log? How do I fix? [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 3 years ago.
I just got done one part of my code and went to launch the app and everything went fine. The build was successful and no issues were found. I then go to the emulator and the app doesn't launch and the log shows a lot of error.
Anyone know where I messed up and how I can fix it.Below is the errors from the log that I receive and I also pasted in the code that I was working on.
2019-05-07 13:06:14.358 22792-22792/com.example.drunktankfix E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.drunktankfix, PID: 22792
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.drunktankfix/com.example.drunktankfix.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(int)' on a null object reference
at com.example.drunktankfix.MainActivity.onCreate(MainActivity.java:55)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:193) 
at android.app.ActivityThread.main(ActivityThread.java:6669) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 
2019-05-07 13:06:16.368 22792-22792/com.example.drunktankfix I/Process: Sending signal. PID: 22792 SIG: 9
Also here is the code:
package com.example.drunktankfix;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import com.example.drunktankfix.AppFragment;
import com.example.drunktankfix.BlacklistFragment;
import com.example.drunktankfix.HelpFragment;
import com.example.drunktankfix.HomeFragment;
//implement the interface OnNavigationItemSelectedListener in your activity class
public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener {
Button Save;
EditText edt1, edt2, edt3;
int in;
Float fl;
String st;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//loading the default fragment
loadFragment(new HomeFragment());
//getting bottom navigation view and attaching the listener
BottomNavigationView navigation = findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(this);
Save = (Button) findViewById(R.id.BtnSave);
edt1 = (EditText) findViewById(R.id.editText1);
edt2 = (EditText) findViewById(R.id.editText2);
edt3 = (EditText) findViewById(R.id.editText3);
// to Retrieve the Data from the SharedPref
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
int in1= prefs.getInt("in",0);
edt1.setText(in1);
float fl1 = prefs.getFloat("fl", 0);
edt2.setText(""+fl1);
String st1 = prefs.getString("st","");
edt3.setText(st1);
Save.setOnClickListener (new View.OnClickListener() {
#Override
public void onClick(View v) {
in = Integer.parseInt(edt1.getText().toString());
fl = Float.parseFloat(edt2.getText().toString());
st = edt3.getText().toString();
// To save the data that is entered
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(MainActivity.this);
SharedPreferences.Editor editor = prefs.edit();
editor.putInt("in", in);
editor.putFloat("fl", fl);
editor.putString("st", st);
editor.apply();
}
});
}
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
Fragment fragment = null;
switch (item.getItemId()) {
case R.id.navigation_home:
fragment = new HomeFragment();
break;
case R.id.navigation_Apps:
fragment = new AppFragment();
break;
case R.id.navigation_Blacklist:
fragment = new BlacklistFragment();
break;
case R.id.navigation_Help:
fragment = new HelpFragment();
break;
}
return loadFragment(fragment);
}
private boolean loadFragment(Fragment fragment) {
//switching fragment
if (fragment != null) {
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_container, fragment)
.commit();
return true;
}
return false;
}
}

You can not enter int value inside the edit text . Try to make it string.
edt1.setText(in1+"");

To set the integer propertly do the following:
edt1.setText("" + integer);
or better solution:
edt1.setText(String.valueOf(integer));

I am not sure how are you getting Nullpointer Exception But from the I code, I see any issue with your here.
editText.setText(Integer Value)
You are setting integer value to Edit text, So that in turn tries to get String resource based on the integer which you set to EditText.That should throw Resource not found Exception not NPE.

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);
}