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NullPointerException on TextView using setText()

I'm rather new to android programming, and am running into my old friend the NullPointerException...
I've been on it for quite a while now, but can't figure out what is wrong.
basicly gives me a NullPointerException when I try to call any .setText() methods, maybe someone sees what I'm doing wrong here...(though i tried to follow examples as close as possible)
public class lessonView extends Activity {
TextView adressOfLecture;
TextView lecturer;
TextView lesson;
Lecture lecture;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lesson_view);
Bundle data = getIntent().getExtras();
lecture = (Lecture) data.getParcelable("student");
adressOfLecture = (TextView)findViewById(R.id.lectureViewAdressLabel);
lecturer = (TextView)findViewById(R.id.lectureViewLecturerLabel);
lesson = (TextView)findViewById(R.id.lectureViewTitle);
updateLabels();
}
#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_lesson_view, 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);
}
private void updateLabels(){
adressOfLecture.setText(lecture.getRoom());
lecturer.setText(lecture.getTutor());
lesson.setText(lecture.getName());
}
}
also, here's my xml file:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.coronarip7.app.stupla.lessonView">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="(ort)"
android:id="#+id/lectureViewAdressLabel"
android:layout_centerVertical="true"
android:layout_toStartOf="#+id/lectureViewTitle"
android:layout_marginRight="86dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="dozent"
android:id="#+id/lectureViewLecturerLabel"
android:layout_toEndOf="#+id/lectureViewTitle"
android:layout_alignTop="#+id/lectureViewAdressLabel"
android:layout_alignParentEnd="true"
android:layout_marginRight="27dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/lectureViewTitle"
android:gravity="center_horizontal"
android:text="test"
android:textSize="40dp"
android:textStyle="bold"
android:padding="10dp"
android:layout_row="0"
android:layout_column="0"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
and the logcat I'm getting:
04-25 01:23:51.058 12236-12236/com.coronarip7.app.stupla E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.coronarip7.app.stupla, PID: 12236
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.coronarip7.app.stupla/com.coronarip7.app.stupla.lessonView}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
at android.app.ActivityThread.access$800(ActivityThread.java:145)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5081)
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:781)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.coronarip7.app.stupla.lessonView.updateLabels(lessonView.java:59)
at com.coronarip7.app.stupla.lessonView.onCreate(lessonView.java:31)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
            at android.app.ActivityThread.access$800(ActivityThread.java:145)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5081)
            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:781)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
            at dalvik.system.NativeStart.main(Native Method)
seriously, I am out of ideas on how to fix it...

First check if you properly put the extra in the intent. Then I would use the following test in your onCreate method:
Intent intent = getIntent();
if (intent.hasExtra("student")){
lecture = (Lecture) intent.getParcelableExtra("student");
}
Then test if lecture is null like Rami wrote earlier.

Ok guys, thanks for the suggestions, but I'll go the global route. I'll create a static version of my array (from which i wanted to pass an object via the Intent), and just pass an int[] array with the coordiantes and call it in the new view.
But thanks for the quick answers anyways!
(I'm new to stackoverflow, is there a way to mark a question as "solved", or "not-needed-to-be-solved-anymore"?)

Do not use static objects in your code like arrays, objects, they have globally available, you should create intent and add your data into your intent like and call your activity
Intent intent = new Intent ();
intent.putExtra ("student",value);
start activity with intent
And in your
lessonViewActivity check for intent like
Intent intent = getIntent();
if (intent.hasExtra("student")){
lecture = (Lecture) intent.getParcelableExtra("student");
if (lecture !=null){
updateLabels ();
}
}

Fatal exception:main Android Eclipse

I am new on android and trying to develop simple calculator but this Fatal exception : main occurs please help.
I did comment my onClickListner to check but it did'nt helped at all.
package com.example.calculatorsinglescreen;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends ActionBarActivity {
EditText value1,value2,myoperator,result;
Button ok;
String strvalue1,strvalue2,stroperator,strresult;
int ivalue1,ivalue2,ioperator,iresult;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
value1 = (EditText) findViewById(R.id.txtvalue1);
value2 = (EditText) findViewById(R.id.txtvalue2);
myoperator = (EditText) findViewById(R.id.txtoperator);
result = (EditText) findViewById(R.id.txtresult);
ok = (Button) findViewById(R.id.btnok);
strvalue1 = value1.getText().toString();
strvalue2 = value2.getText().toString();
stroperator = myoperator.getText().toString();
ivalue1 = Integer.parseInt(strvalue1);
ivalue2 = Integer.parseInt(strvalue2);
ok.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
if (stroperator.equals("+")) {
Toast msg = Toast.makeText(MainActivity.this, "If is running", Toast.LENGTH_LONG);
msg.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.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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
This is my XML file :
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.calculatorsinglescreen.MainActivity" >
<TextView
android:id="#+id/value1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_margin="20dp"
android:text="Value 1" />
<TextView
android:id="#+id/value2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/value1"
android:layout_margin="20dp"
android:text="Value 2" />
<TextView
android:id="#+id/operator"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/value2"
android:layout_margin="20dp"
android:text="Operator" />
<EditText
android:id="#+id/txtvalue1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_toRightOf="#+id/value1"
android:layout_alignBaseline="#+id/value1"
android:layout_alignParentRight="true"
android:ems="10" >
<requestFocus />
</EditText>
<EditText
android:id="#+id/txtoperator"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/operator"
android:layout_below="#+id/txtvalue2"
android:layout_toRightOf="#+id/operator"
android:layout_alignParentRight="true"
android:ems="10" />
<EditText
android:id="#+id/txtvalue2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/value2"
android:layout_toRightOf="#+id/value2"
android:layout_below="#+id/txtvalue1"
android:layout_alignParentRight="true"
android:ems="10" />
<Button
android:id="#+id/btnok"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:text="Ok" />
<TextView
android:id="#+id/result"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/btnok"
android:layout_margin="40dp"
android:text="Result" />
<EditText
android:id="#+id/txtresult"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/result"
android:layout_toRightOf="#+id/result"
android:ems="10" />
Here is my LogCat to get a clearer view :
10-18 17:51:25.468: D/AndroidRuntime(742): Shutting down VM
10-18 17:51:25.468: W/dalvikvm(742): threadid=1: thread exiting with uncaught exception (group=0x40015560)
10-18 17:51:25.488: E/AndroidRuntime(742): FATAL EXCEPTION: main
10-18 17:51:25.488: E/AndroidRuntime(742): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.calculatorsinglescreen/com.example.calculatorsinglescreen.MainActivity}: java.lang.NumberFormatException: unable to parse '' as integer
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.os.Handler.dispatchMessage(Handler.java:99)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.os.Looper.loop(Looper.java:123)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.ActivityThread.main(ActivityThread.java:3683)
10-18 17:51:25.488: E/AndroidRuntime(742): at java.lang.reflect.Method.invokeNative(Native Method)
10-18 17:51:25.488: E/AndroidRuntime(742): at java.lang.reflect.Method.invoke(Method.java:507)
10-18 17:51:25.488: E/AndroidRuntime(742): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-18 17:51:25.488: E/AndroidRuntime(742): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-18 17:51:25.488: E/AndroidRuntime(742): at dalvik.system.NativeStart.main(Native Method)
10-18 17:51:25.488: E/AndroidRuntime(742): Caused by: java.lang.NumberFormatException: unable to parse '' as integer
10-18 17:51:25.488: E/AndroidRuntime(742): at java.lang.Integer.parseInt(Integer.java:362)
10-18 17:51:25.488: E/AndroidRuntime(742): at java.lang.Integer.parseInt(Integer.java:332)
10-18 17:51:25.488: E/AndroidRuntime(742): at com.example.calculatorsinglescreen.MainActivity.onCreate(MainActivity.java:34)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-18 17:51:25.488: E/AndroidRuntime(742): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
10-18 17:51:25.488: E/AndroidRuntime(742): ... 11 more

this is the error
java.lang.ClassCastException: android.widget.TextView
check your line 24 and see if you cast the right widget in java -(xml), this error means incompatible cast widget lol...
if everything seems correct-(mean widgets are cast in java to with their respective class) then clean rebuild and restart..
EDIT: It worked.. you've solved it but there is a new error which is
java.lang.NumberFormatException:
its because of this on these lines
ivalue1 = Integer.parseInt(strvalue1);
ivalue2 = Integer.parseInt(strvalue2);
ioperator = Integer.parseInt(stroperator);
so change these to this
Integer.valueOf(strvalue1); do that as follows
and also looking at your codes.. your string values are pullled from the edittext during oncreate which means when the app starts in oncreate before the Onresume(which is called when the app shows on the), and during oncreate the user cant flirt with your app, and going further to input values, so at the end your strings are empty when you pull from the edittext, so basically what im saying is remove these lines
strvalue1 = value1.getText().toString();
and put them in the click events ... i am lucid enough to you??..
EDIT2: OVERALL CODE
for button click
ok.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
strvalue1 = value1.getText().toString();
strvalue2 = value2.getText().toString();
stroperator = myoperator.getText().toString();
ivalue1 = Integer.valueOf(strvalue1);
ivalue2 = Integer.valueOf(strvalue2);
if (stroperator.equals("+")) {
Toast.makeText(MainActivity.this, "If is running", Toast.LENGTH_LONG).show();
}
}
});

remove ioperator = Integer.parseInt(stroperator); from the code.I think Your trying to convert the operator to Integer.

ioperator = Integer.parseInt(stroperator);
if you mean operator like this +,-,/,* , you only can convert to thr char or stay in string and do something like this:
private int plus(int ivalue1 , int ivalue2 , String operator ){
if(operator.equal("+")){
return ivalue1 + ivalue2;
}
return 0;
}

Crash when adding a OnClickListener to a Button

I'm a total newbie with Android, and I'm trying to switch between two activities ("MainActivity" and "LoginDisplayActivity") and adding the "OnClickListener" seem to make my app crash on startup.
Here is my code :
package info.dremor.kronos;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.os.Build;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(savedInstanceState == null) {
getFragmentManager().beginTransaction().add(R.id.container, new MainFragment()).commit();
}
final Button loginButton = (Button) findViewById(R.id.connect);
loginButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, LoginDisplayActivity.class);
startActivity(intent);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class MainFragment extends Fragment {
public MainFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
trace :
05-26 15:48:11.286: D/AndroidRuntime(947): Shutting down VM
05-26 15:48:11.286: W/dalvikvm(947): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
05-26 15:48:11.296: E/AndroidRuntime(947): FATAL EXCEPTION: main
05-26 15:48:11.296: E/AndroidRuntime(947): java.lang.RuntimeException: Unable to start activity ComponentInfo{info.dremor.kronos/info.dremor.kronos.MainActivity}: java.lang.NullPointerException
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.ActivityThread.access$600(ActivityThread.java:130)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.os.Handler.dispatchMessage(Handler.java:99)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.os.Looper.loop(Looper.java:137)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.ActivityThread.main(ActivityThread.java:4745)
05-26 15:48:11.296: E/AndroidRuntime(947): at java.lang.reflect.Method.invokeNative(Native Method)
05-26 15:48:11.296: E/AndroidRuntime(947): at java.lang.reflect.Method.invoke(Method.java:511)
05-26 15:48:11.296: E/AndroidRuntime(947): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
05-26 15:48:11.296: E/AndroidRuntime(947): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-26 15:48:11.296: E/AndroidRuntime(947): at dalvik.system.NativeStart.main(Native Method)
05-26 15:48:11.296: E/AndroidRuntime(947): Caused by: java.lang.NullPointerException
05-26 15:48:11.296: E/AndroidRuntime(947): at info.dremor.kronos.MainActivity.onCreate(MainActivity.java:31)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.Activity.performCreate(Activity.java:5008)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
05-26 15:48:11.296: E/AndroidRuntime(947): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
05-26 15:48:11.296: E/AndroidRuntime(947): ... 11 more
activity_main.xml :
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="info.dremor.kronos.MainActivity"
tools:ignore="MergeRootFrame" />
fragment_main.xml :
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="info.dremor.kronos.MainActivity$PlaceholderFragment" >
<Button
android:id="#+id/connect"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="35dp"
android:text="#string/connect" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="35dp"
android:text="#string/login_greeting" />
<TextView
android:id="#+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/textView1"
android:layout_centerHorizontal="true"
android:layout_marginTop="35dp"
android:text="#string/login" />
<EditText
android:id="#+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/textView3"
android:layout_centerHorizontal="true"
android:layout_marginTop="35dp"
android:ems="10" />
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/editText1"
android:layout_centerHorizontal="true"
android:layout_marginTop="35dp"
android:text="#string/password" />
<EditText
android:id="#+id/editText2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/editText1"
android:layout_below="#+id/textView2"
android:layout_marginTop="35dp"
android:ems="10"
android:inputType="textPassword" />
</RelativeLayout>
Can someone help me?

In your activity, you set the layout file like this:
setContentView(R.layout.activity_main);
This means, when you write findViewById, it will look within the activity_main.xml file.
Your button on the other hand is within another layout file.
Just move the click event into your fragment, and access the context using getActivity like so:
final Button loginButton = (Button) rootView.findViewById(R.id.connect);
loginButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(getActivity(), LoginDisplayActivity.class);
startActivity(intent);
}
});

your button is in the fragment layout, you're "finding" it from the activity layout. Setup button onclick in the fragment onCreateView
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
final Button loginButton = (Button) rootView.findViewById(R.id.connect);
loginButton.setOnClickListener(new OnClickListener(){...})
return rootView;
}

Remove the button and code from onCreate and shift the button and clicklistener code to onCreateView like this:
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
final Button loginButton = (Button) rootView.findViewById(R.id.connect);
loginButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, LoginDisplayActivity.class);
startActivity(intent);
}
});
return rootView;
As your button is in fragment_main, not activity_main. The button is not found.

FATAL EXCEPTION: main. (Runtime exception) . Android

I'm new to android. I just tried creating a simple app that performs basic mathematical operations (addition,subtraction,multiplication and division). When i try to run the code i get FATAL EXCEPTION: mainerror. I've gone through the other threads that had the same problem. I still couldn't figure out why i'm having this error.
The mainactivity.java file is
package com.example.mathematicalopr;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
Button add,sub,mul,div;
TextView display2;
EditText display,display1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//int c=0;
add = (Button) findViewById(R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
mul = (Button) findViewById(R.id.times);
div = (Button) findViewById(R.id.divide);
display = (EditText) findViewById(R.id.tvDisplay);
String myFirstNum = display.getText().toString();
final int a = Integer.parseInt(myFirstNum);
display1 = (EditText) findViewById(R.id.tvDisplay1);
String mySecondNum = display1.getText().toString();
final int b = Integer.parseInt(mySecondNum);
display2 = (TextView) findViewById(R.id.tvDisplay2);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
int c = a+b;
display2.setText("Answer is"+c);
}
});
sub.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
int c = a-b;
display2.setText("Answer is"+c);
}
});
mul.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
int c = a*b;
display2.setText("Answer is"+c);
}
});
div.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
int c = a/b;
display2.setText("Answer is"+c);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
My activity_main.xml file is
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<EditText
android:id="#+id/tvDisplay"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:inputType="number"
android:text="#string/ref" />
<EditText
android:id="#+id/tvDisplay1"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:inputType="number"
android:text="#string/ref1" />
<Button
android:id="#+id/bAdd"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/add" />
<Button
android:id="#+id/bSub"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/sub" />
<Button
android:id="#+id/times"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/times" />
<Button
android:id="#+id/divide"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/divide" />
<TextView
android:id="#+id/tvDisplay2"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:text="#string/ref2" />
</LinearLayout>
My strings.xml file
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">Mathematicalopr</string>
<string name="action_settings">Settings</string>
<string name="hello_world">Hello world!</string>
<string name="ref">Enter first number</string>
<string name="add">Add</string>
<string name="sub">Subtract </string>
<string name="times">Multiply</string>
<string name="divide">divide</string>
<string name="ref1">Enter second number</string>
<string name="ref2">Answer is</string>
</resources>
Logcat:
02-08 10:50:43.962: W/Trace(2302): Unexpected value from nativeGetEnabledTags: 0
02-08 10:50:43.972: W/Trace(2302): Unexpected value from nativeGetEnabledTags: 0
02-08 10:50:43.972: W/Trace(2302): Unexpected value from nativeGetEnabledTags: 0
02-08 10:50:44.022: W/Trace(2302): Unexpected value from nativeGetEnabledTags: 0
02-08 10:50:44.022: W/Trace(2302): Unexpected value from nativeGetEnabledTags: 0
02-08 10:50:44.422: D/AndroidRuntime(2302): Shutting down VM
02-08 10:50:44.432: W/dalvikvm(2302): threadid=1: thread exiting with uncaught exception (group=0xb2ca6908)
02-08 10:50:44.462: E/AndroidRuntime(2302): FATAL EXCEPTION: main
02-08 10:50:44.462: E/AndroidRuntime(2302): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mathematicalopr/com.example.mathematicalopr.MainActivity}: java.lang.NumberFormatException: Invalid int: "Enter first number"
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.os.Handler.dispatchMessage(Handler.java:99)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.os.Looper.loop(Looper.java:137)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.ActivityThread.main(ActivityThread.java:5039)
02-08 10:50:44.462: E/AndroidRuntime(2302): at java.lang.reflect.Method.invokeNative(Native Method)
02-08 10:50:44.462: E/AndroidRuntime(2302): at java.lang.reflect.Method.invoke(Method.java:511)
02-08 10:50:44.462: E/AndroidRuntime(2302): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-08 10:50:44.462: E/AndroidRuntime(2302): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-08 10:50:44.462: E/AndroidRuntime(2302): at dalvik.system.NativeStart.main(Native Method)
02-08 10:50:44.462: E/AndroidRuntime(2302): Caused by: java.lang.NumberFormatException: Invalid int: "Enter first number"
02-08 10:50:44.462: E/AndroidRuntime(2302): at java.lang.Integer.invalidInt(Integer.java:138)
02-08 10:50:44.462: E/AndroidRuntime(2302): at java.lang.Integer.parse(Integer.java:375)
02-08 10:50:44.462: E/AndroidRuntime(2302): at java.lang.Integer.parseInt(Integer.java:366)
02-08 10:50:44.462: E/AndroidRuntime(2302): at java.lang.Integer.parseInt(Integer.java:332)
02-08 10:50:44.462: E/AndroidRuntime(2302): at com.example.mathematicalopr.MainActivity.onCreate(MainActivity.java:30)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.Activity.performCreate(Activity.java:5104)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
02-08 10:50:44.462: E/AndroidRuntime(2302): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
02-08 10:50:44.462: E/AndroidRuntime(2302): ... 11 more
Can i know why am i getting such an error? When i try to run this code on a virtual device the application closes unexpectedly. Thank you :)
Thank you everyone. Sorry apparently i don't have enough reputation to thank each one of you personally.

String myFirstNum = display.getText().toString();
final int a = Integer.parseInt(myFirstNum);
String mySecondNum = display1.getText().toString();
final int b = Integer.parseInt(mySecondNum);
insert this code in your add button click event listener then you will get correct data

Your Logcat say it all,
Read this
Invalid int: "Enter first number"
Your are casting a string value to int, which results java.lang.NumberFormatException.

you must change
<EditText
android:id="#+id/tvDisplay"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:inputType="number"
android:hint="#string/ref" />
<EditText
android:id="#+id/tvDisplay1"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:inputType="number"
android:hint="#string/ref1" />
you must change from
android:text="#string/ref1"
to
android:hint="#string/ref1"
because on oncreate() method you are retrieving value of EditText. And in xml you have set string for it and after that you have parsed it in Integer. So you have got invalid int error. So just change it for every EditText.
Your are casting a string value to int, which results java.lang.NumberFormatException.

Modified your code:
package com.example.sampleactivity;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
Button add,sub,mul,div;
TextView display2;
EditText display,display1;
int a,b,c;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//int c=0;
add = (Button) findViewById(R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
mul = (Button) findViewById(R.id.times);
div = (Button) findViewById(R.id.divide);
display = (EditText) findViewById(R.id.tvDisplay);
display1 = (EditText) findViewById(R.id.tvDisplay1);
display2 = (TextView) findViewById(R.id.tvDisplay2);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
getValues();
c = a+b;
display2.setText("Answer is"+c);
}
});
sub.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
getValues();
c = a-b;
display2.setText("Answer is"+c);
}
});
mul.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
getValues();
c = a*b;
display2.setText("Answer is"+c);
}
});
div.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
getValues();
c = a/b;
display2.setText("Answer is"+c);
}
});
}
protected void getValues() {
String myFirstNum = display.getText().toString();
a= Integer.parseInt(myFirstNum);
String mySecondNum = display1.getText().toString();
b = Integer.parseInt(mySecondNum);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<EditText
android:id="#+id/tvDisplay"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:hint="#string/ref"
android:inputType="number" />
<EditText
android:id="#+id/tvDisplay1"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:hint="#string/ref1"
android:inputType="number" />
<Button
android:id="#+id/bAdd"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/add" />
<Button
android:id="#+id/bSub"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/sub" />
<Button
android:id="#+id/times"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/times" />
<Button
android:id="#+id/divide"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="#string/divide" />
<TextView
android:id="#+id/tvDisplay2"
android:layout_width="342dp"
android:layout_height="wrap_content"
android:text="#string/ref2" />
</LinearLayout>

getting null pointer exception

I am getting a NullPointerException when I try to access text view which is defined in view class. I am accessing it from setting class. A small part of my code is:
view class
public class view1 extends menu {
public static TextView text1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view);
text1=(TextView)findViewById(R.id.textfile1);
text1.setText("product");
}
public void small(String mytext) { // this is my method which I want to access
text1.setText(mytext);
}
}
setting class
public class Setting extends Activity {
private Spinner spinner1;
private Button apply;
TextView small1;
private view1 view11;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.setting);
//setContentView(R.layout.view);
addItemsOnSpinner1();
addListenerOnSpinnerItemSelection();
}
public void addItemsOnSpinner1() {
spinner1 = (Spinner) findViewById(R.id.spinner1);
List<String> list = new ArrayList<String>();
list.add("Small");
list.add("Medium");
list.add("Large");
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, list);
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner1.setAdapter(dataAdapter);
}
public void addListenerOnSpinnerItemSelection() {
spinner1 = (Spinner) findViewById(R.id.spinner1);
apply = (Button) findViewById(R.id.apply);
spinner1.setOnItemSelectedListener(new CustomOnItemSelectedListener());
apply.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
String mytext = "Something else";
view11.small(mytext);
}
Stack trace
01-17 00:11:02.064: E/AndroidRuntime(4191): FATAL EXCEPTION: main
01-17 00:11:02.064: E/AndroidRuntime(4191): java.lang.NullPointerException
01-17 00:11:02.064: E/AndroidRuntime(4191): at com.ramanrayat.notelet.Setting$1.onClick(Setting.java:106)
01-17 00:11:02.064: E/AndroidRuntime(4191): at android.view.View.performClick(View.java:4240)
01-17 00:11:02.064: E/AndroidRuntime(4191): at android.view.View$PerformClick.run(View.java:17721)
01-17 00:11:02.064: E/AndroidRuntime(4191): at android.os.Handler.handleCallback(Handler.java:730)
01-17 00:11:02.064: E/AndroidRuntime(4191): at android.os.Handler.dispatchMessage(Handler.java:92)
01-17 00:11:02.064: E/AndroidRuntime(4191): at android.os.Looper.loop(Looper.java:137)
01-17 00:11:02.064: E/AndroidRuntime(4191): at android.app.ActivityThread.main(ActivityThread.java:5103)
01-17 00:11:02.064: E/AndroidRuntime(4191): at java.lang.reflect.Method.invokeNative(Native Method)
01-17 00:11:02.064: E/AndroidRuntime(4191): at java.lang.reflect.Method.invoke(Method.java:525)
01-17 00:11:02.064: E/AndroidRuntime(4191): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-17 00:11:02.064: E/AndroidRuntime(4191): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-17 00:11:02.064: E/AndroidRuntime(4191): at dalvik.system.NativeStart.main(Native Method)
setting.xml code
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/RelativeLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="horizontal" >
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="38dp"
android:text="Setting"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="40dp" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/textView2"
android:layout_centerHorizontal="true"
android:layout_marginTop="57dp"
android:gravity="center"
android:text="Font Size"
android:textSize="30dp" />
<Spinner
android:id="#+id/spinner1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/textView1"
android:layout_marginTop="30dp" />
<Button
android:id="#+id/apply"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/textView1"
android:layout_alignRight="#+id/textView2"
android:layout_below="#+id/spinner1"
android:layout_marginTop="58dp"
android:text="Apply" />
</RelativeLayout>

Chnage
if(String.valueOf(spinner1.getSelectedItem())=="Small")
TO
if(String.valueOf(spinner1.getSelectedItem()).equals("Small"))
Use .equals or .equalsIgnoreCase to compare strings
Instead of making textview static you should use intents to pass values between activities.
Intent intent = new Intent(ActivityName.this,Settings.class);
intent.putExtra("key",text1.getText().toString());
startActivity(intent);
Then
String value = getIntent().getStringExtra("key");
Change
public static TextView text1;
to
public TextView text1;
Also follow java naming conventions

Replace
public static TextView text1;
with
TextView text1;
text1 can not be static.
Next time, please click on the file name in the error log and indicate which line number in your code listing is the line that the error actually points to.
Learn to start all your class names with capital letters (athough, this is not what's causing the problem). And while I'm at it, please stop using numbers in class names and in variables, especially the number 1, which can be ambiguously read as an "l" in some fonts.

Look for your LogCat, it will told you where is NPE.
The other question is : don't use equals to compare String instead of ==
== is compare two object's address and equals is compare their value.
if(String.valueOf(spinner1.getSelectedItem()).equals("Small")) {
String mytext = "Something else ";
view11.small(mytext); // view11 is clas view1 reference
}
else if(String.valueOf(spinner1.getSelectedItem()).equals("Medium")) {
finish();
}