Develop Reference

How can I redirect 2 buttons to different intents in android?

enter image description here
I put a listener on each button that takes me to different activities.
The login button works perfectly, but the register button stops the app when I click on it.
I've tried to put a Toast message in the _btnreg listener, and it worked...
I got this error:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.virtualshelter, PID: 24128
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.virtualshelter/com.example.android.virtualshelter.register}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6247)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.android.virtualshelter.register.onCreate(register.java:35)
at android.app.Activity.performCreate(Activity.java:6754)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6247) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762) 
package com.example.android.virtualshelter;
import android.content.ContentValues;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.*;
public class MainActivity extends AppCompatActivity
{
Button _btnreg, _btnlogin;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
_btnlogin = findViewById(R.id.btnlogin);
_btnreg = findViewById(R.id.btnreg);
_btnreg.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
Intent intent = new Intent(MainActivity.this,register.class);
startActivity(intent);
}
});
_btnlogin.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
Intent intent = new Intent(MainActivity.this,login.class);
startActivity(intent);
}
});
}
}
My register.java code
package com.example.android.virtualshelter;
import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class register extends AppCompatActivity
{
SQLiteOpenHelper openHelper;
SQLiteDatabase db;
Button _btnReg;
EditText _txtfname, _txtlname, _txtpass, _txtemail, _txtphone;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
openHelper = new DatabaseHelper(register.this);
_txtfname = findViewById(R.id.txtfname);
_txtlname = findViewById(R.id.txtlname);
_txtpass = findViewById(R.id.txtpass);
_txtemail = findViewById(R.id.txtemail);
_txtphone = findViewById(R.id.txtphone);
_btnReg = findViewById(R.id.btnreg);
_btnReg.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
db = openHelper.getWritableDatabase();
String fname = _txtfname.getText().toString();
String lname = _txtlname.getText().toString();
String pass = _txtpass.getText().toString();
String email = _txtemail.getText().toString();
String phone = _txtphone.getText().toString();
insertdata(fname, lname, pass, email, phone);
Toast.makeText(getApplicationContext(), "register successfully", Toast.LENGTH_LONG).show();
}
});
}
public void insertdata(String fname, String lname, String pass, String email, String phone)
{
ContentValues contentValues = new ContentValues();
contentValues.put(DatabaseHelper.COL_2, fname);
contentValues.put(DatabaseHelper.COL_3, lname);
contentValues.put(DatabaseHelper.COL_4, pass);
contentValues.put(DatabaseHelper.COL_5, email);
contentValues.put(DatabaseHelper.COL_6, phone);
long id = db.insert(DatabaseHelper.TABLE_NAME, null, contentValues);
}
}
I expect to go to activity register.java, but the app is crashing

My hunch is, you are not able find the button, causing a NPE when setting the listner. Could be that you don't have the button defined in R.layout.activity_main, but in a different layout.

Android intent error null object reference [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
Hello im new in stackover flow i want to try these website and ask for someones help in my android when i change the intent there's an error in my android monitor in android studio here is it.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.kim.checkerv3, PID: 2970
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.kim.checkerv3/com.example.kim.checkerv3.BudgetOutput}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.BaseBundle.getString(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$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 'java.lang.String android.os.BaseBundle.getString(java.lang.String)' on a null object reference
at com.example.kim.checkerv3.BudgetOutput.onCreate(BudgetOutput.java:22)
at android.app.Activity.performCreate(Activity.java:6664)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6077) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
i didn't understand this i'd tried researching for solution and im still stuck on it.
Here the intent will be pass to other java class.
package com.example.kim.checkerv3;
import android.app.Fragment;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AlertDialog;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import static android.content.Context.MODE_PRIVATE;
/**
* Created by KIM-PC on 12/5/2016.
*/
public class BudgetFragment extends android.support.v4.app.Fragment {
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.activity_budget, container, false);
final EditText etCash = (EditText) v.findViewById(R.id.etCash);
final Button bBudget = (Button) v.findViewById(R.id.bBudget);
bBudget.setOnClickListener(new View.OnClickListener(){
public void onClick(View v) {
SharedPreferences sharedpref = getContext().getSharedPreferences("user_id", MODE_PRIVATE);
String id = sharedpref.getString("user_id","");
final int budgeted = Integer.parseInt(etCash.getText().toString());
Response.Listener<String> responseListener = new Response.Listener<String>() {
#Override
public void onResponse(String response) {
try {
JSONObject jsonResponse = new JSONObject(response);
JSONArray arr = jsonResponse.getJSONArray("message");
boolean success = jsonResponse.getBoolean("success");
System.out.println(budgeted/arr.length());
int total = budgeted/arr.length();
if (success) {
Intent intent = new Intent(getContext(), BudgetOutput.class);
Bundle b = new Bundle();
b.putString("total", String.valueOf(total));
getContext().startActivity(intent);
if (arr != null) {
int sum = 0;
for(int i = 0;i<arr.length();i++){
//listdata.add(arr.get(i).toString());
String money = arr.getJSONObject(i).getString("amount");
sum += Integer.parseInt(money);
}
SharedPreferences sharedPref1 = getActivity().getSharedPreferences("mypref", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref1.edit();
editor.putInt("TotalSum", sum);
editor.commit();
System.out.println(sum);
//arrayAdapter.notifyDataSetChanged();
}
} else {
AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
builder.setMessage("Failed to fetch. Try again.")
.setNegativeButton("OK", null)
.create()
.show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
RecordRequest recordRequest = new RecordRequest(id, responseListener);
RequestQueue queue = Volley.newRequestQueue(getContext());
queue.add(recordRequest);
}
});
return v;
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
SharedPreferences sharedpref1 = getContext().getSharedPreferences("mypref", MODE_PRIVATE);
int budgeted = sharedpref1.getInt("TotalSum", 0);
System.out.println(budgeted/2);
}
}
and the class where the intent will be get.
package com.example.kim.checkerv3;
import android.content.Intent;
import android.os.Bundle;
import android.os.PersistableBundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.EditText;
import android.widget.TextView;
/**
* Created by KIM-PC on 12/6/2016.
*/
public class BudgetOutput extends AppCompatActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_output);
final TextView tvOutput = (TextView) findViewById(R.id.tvoutput);
Bundle b = getIntent().getExtras();
String output=b.getString("total");
if(b !=null)
output = b.getString("total");
tvOutput.setText(output+" Per cheque record.");
}
}
if there is someone who could solve i appreciate and give my thanks to you.

Well, you forgot to add your Bundle to the Intent
Intent intent = new Intent(getContext(), BudgetOutput.class);
Bundle b = new Bundle();
b.putString("total", String.valueOf(total));
intent.putExtras(b);
getContext().startActivity(intent);

E/SQLiteLog: (1) near "ENTER": syntax error

I'm getting this weird error while trying to create a database. I'm building an expense manager app and want to store the data from textview into SQLite database but I'm getting these errors when I press the save button. IS This because I'm trying to create database in another activity rather than the MainActivity??
07-20 01:49:31.032 28795-28795/com.example.alkesh.expensemanager101 E/SQLiteLog: (1) near "ENTER": syntax error
07-20 01:49:31.032 28795-28795/com.example.alkesh.expensemanager101 D/AndroidRuntime: Shutting down VM
--------- beginning of crash
07-20 01:49:31.042 28795-28795/com.example.alkesh.expensemanager101 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.alkesh.expensemanager101, PID: 28795
Theme: themes:{default=overlay:com.baranovgroup.nstyle, iconPack:com.baranovgroup.nstyle, fontPkg:com.baranovgroup.nstyle, com.android.systemui=overlay:com.baranovgroup.nstyle, com.android.systemui.navbar=overlay:com.baranovgroup.nstyle}
android.database.sqlite.SQLiteException: near "ENTER": syntax error (code 1): , while compiling: ENTER INTO money (name) VALUES ('25');
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:1674)
at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1605)
at com.example.alkesh.expensemanager101.AddMoney.insertIntoDatabase(AddMoney.java:95)
at com.example.alkesh.expensemanager101.AddMoney.onClick(AddMoney.java:63)
at android.view.View.performClick(View.java:5204)
at android.view.View$PerformClick.run(View.java:21158)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5461)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
Here's my code for the AddMoney Activity
package com.example.alkesh.expensemanager101;
import android.content.Context;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class AddMoney extends AppCompatActivity implements View.OnClickListener{
Button Save,Cancel;
EditText expText;
int[] expense=new int[100];
int temp=900;
int c=0;
int sum=0;
String DBOnce;
private SQLiteDatabase db;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_money);
expText=(EditText)findViewById(R.id.expense);
Cancel=(Button)findViewById(R.id.cancelbutton);
Cancel.setOnClickListener(this);
Save = (Button)findViewById(R.id.savebutton);
Save.setOnClickListener(this);
CreateDatabase();
}
#Override
public void onClick(View view) {
if(view== Save){
insertIntoDatabase();
}
if(view==Cancel){
Intent intent =new Intent(AddMoney.this,MainActivity.class);
startActivity(intent);
finish();
}
}
protected void CreateDatabase(){
db=openOrCreateDatabase("MoneyDB", Context.MODE_PRIVATE,null);
db.execSQL("CREATE TABLE IF NOT EXISTS money(ID INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, name VARCHAR);");
}
protected void insertIntoDatabase(){
String amount = expText.getText().toString().trim();
if(amount.equals("")){
Toast.makeText(this,"Please enter your expense or press Cancel to go back",Toast.LENGTH_LONG).show();
return;
}
String query="ENTER INTO money (name) VALUES ('"+amount+"');";
db.execSQL(query);
Toast.makeText(this,"Expense Saved",Toast.LENGTH_LONG).show();
}
}
Here's my code for MainActivity.
package com.example.alkesh.expensemanager101;
import android.content.Intent;
import android.os.Parcelable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
Button Add;
TextView expense;
int c=0;
String DBonce="0";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Add = (Button) findViewById(R.id.addbutton);
Add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, AddMoney.class);
intent.putExtra("counter", DBonce);
startActivity(intent);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menuhome,menu);
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()){
case R.id.feedback:{}
break;
case R.id.exit: finish();
break;
}
return super.onOptionsItemSelected(item);
}
}

In AddMoney Activity function insertIntoDatabase() change your query Enter to INSERT

Error receiving broadcast intent using BatteryManager

I am getting Error in receiving broadcast intent i am using BatteryManager for it. I have no clue why I am getting this error.
Someone please help.
thanks in advance
Let me know if you need more code.
Here is the error:
> Error receiving broadcast Intent {
> act=android.intent.action.BATTERY_CHANGED flg=0x60000010 (has extras)
> } in com.example.android.login.MainActivity$1#260e12dc
> at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:933)
> at android.os.Handler.handleCallback(Handler.java:739)
> at android.os.Handler.dispatchMessage(Handler.java:95)
> at android.os.Looper.loop(Looper.java:145)
> at android.app.ActivityThread.main(ActivityThread.java:5972)
> at java.lang.reflect.Method.invoke(Native Method)
> at java.lang.reflect.Method.invoke(Method.java:372)
> at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388)
> at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183)
> Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
> android.widget.TextView.setText(java.lang.CharSequence)' on a null
> object reference
> at com.example.android.login.MainActivity$1.onReceive(MainActivity.java:37)
> at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:923)
>             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:5972)
>             at java.lang.reflect.Method.invoke(Native Method)
>             at java.lang.reflect.Method.invoke(Method.java:372)
Activity Class
package com.example.android.login;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.Resources;
import android.os.BatteryManager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import com.parse.LogOutCallback;
import com.parse.Parse;
import com.parse.ParseObject;
import com.parse.ParseUser;
import com.parse.ParseException;
public class MainActivity extends ActionBarActivity {
private TextView batteryTxt;
private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver(){
#Override
public void onReceive(Context ctxt, Intent intent) {
int level = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0);
batteryTxt.setText(String.valueOf(level) + "%");
}
};
private Toolbar toolbar;
public Button logoutButton;
public int level;
#Override
public void onCreate(Bundle savedInstanceState) {
batteryTxt = (TextView) this.findViewById(R.id.percent);
this.registerReceiver(this.mBatInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_appbar);
toolbar = (Toolbar) findViewById(R.id.app_bar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawerLayout), toolbar);
logoutButton = (Button) findViewById(R.id.logoutButton);
logoutButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Set up a progress dialog
final ProgressDialog logout = new ProgressDialog(MainActivity.this);
logout.setTitle("Please wait.");
logout.setMessage("Logging out. Please wait.");
logout.show();
ParseUser.logOutInBackground(new LogOutCallback() {
public void done(ParseException e) {
logout.dismiss();
if (e == null) {
Intent logoutDone = new Intent(MainActivity.this, DispatchActivity.class);
startActivity(logoutDone);
} else {
Toast.makeText(MainActivity.this, "Logout Unsuccessful", Toast.LENGTH_LONG).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);
}
}

Based on your stack trace, it looks like it is throwing a NullPointerException because the batteryTxt field is null at the time that the intent was received. As Daniel Nugent pointed out, this is because the receiver is registered before calling setContentView(). However, it looks like you're also never unregistering your receiver, so I suggest moving the code to register the receiver to the onResume() method, and adding an unregister call in the onPause() method to prevent this same NullPointerException from occurring when your activity is stopped.
#Override
protected void onResume() {
super.onResume();
registerReceiver(mBatInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
}
#Override
protected void onPause() {
unregisterReceiver(mBatInfoReceiver);
super.onPause();
}

do this
batteryTxt = (TextView) this.findViewById(R.id.percent);
after this
setContentView(R.layout.activity_main_appbar);
always read this section in your error log
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
Write the code like that
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_appbar);
toolbar = (Toolbar) findViewById(R.id.app_bar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
batteryTxt = (TextView) this.findViewById(R.id.percent);
this.registerReceiver(this.mBatInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

Error while opening Android app

i am new to android development and i am writing an app for my college project .The app transmits a string of data stored in shared preferences .The data is stored by one time setup screen which is never shown again.The issue is after first time,when app is started again it shows that "app has unfortunately stopped working "and when i click ok the app starts.Can anybody tell me why this is happening?
Code:
package com.example.homeautomation.zigbeehomeauto;
import android.annotation.TargetApi;
import android.content.SharedPreferences;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.os.Build;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.Toast;
public class MainScreen extends ActionBarActivity {
NdefMessage msg;
NfcAdapter nfcadapter;
public static final String PREFS_NAME = "MyPrefsFile";
public String pass2 ;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_screen);
SharedPreferences check = getSharedPreferences(PREFS_NAME, 0);
String Pass = check.getString("Str", "Nothing");
pass2 = Pass;
nfcadapter = NfcAdapter.getDefaultAdapter(this);
if (nfcadapter == null) {
Toast.makeText(this, "NFC is not available User", Toast.LENGTH_LONG)
.show();
finish();
}
}
public void ExApp(View v) {
finish();
System.exit(0);
}
#TargetApi(Build.VERSION_CODES.JELLY_BEAN)
public void Nsend(View v)
{
byte[] stringBytes = pass2.getBytes();
nfcadapter.setNdefPushMessage(msg = new NdefMessage(new NdefRecord[]{NdefRecord.createMime("text/plain", stringBytes)
}),this);
}
}
Logcat Ouput:
04-07 12:04:38.478 10836-10836/com.example.homeautomation.zigbeehomeauto E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.homeautomation.zigbeehomeauto, PID: 10836
android.util.SuperNotCalledException: Activity {com.example.homeautomation.zigbeehomeauto/com.example.homeautomation.zigbeehomeauto.SetupScreen} did not call through to super.onCreate()
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2510)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2603)
at android.app.ActivityThread.access$900(ActivityThread.java:174)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5752)
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:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)

Check in your SetupScreen.java do you have super.onCreate(savedInstanceState);
after onCreate() Method is starts .
post your SetupScreen.java code also ..

Your onCreate() method of class SetupScreen do not call the super.onCreate(). Add the statement and the error should go away.