We Keep Coding

Android : Saving and Restoring Activity data when switching Portrait and Landscape

I am try to save my roll no and name in main activity but when my screen is rotated the activity data has been lose ,
finally i fixed it , below i adding source code

consider any layout , here i am using this layout structure
In activity_xml :
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="20dp"
tools:context=".MainActivity">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:id="#+id/rollnoID"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="15dp"
android:layout_marginTop="10dp"
android:text="Rollno : "
android:textSize="25dp" />
<EditText
android:hint="Roll Number"
android:id="#+id/rollnoID_edit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="15dp"
android:layout_marginTop="10dp"
android:ems="8"
android:inputType="number"
android:text=""
android:textSize="25dp" />
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:id="#+id/nameID"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="15dp"
android:layout_marginTop="10dp"
android:text="Name : "
android:textSize="25dp" />
<EditText
android:hint="Student Name"
android:id="#+id/nameID_edit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="15dp"
android:layout_marginTop="10dp"
android:ems="8"
android:inputType="textCapWords"
android:text=""
android:textSize="25dp" />
</LinearLayout>
<Button
android:onClick="saveData"
android:id="#+id/saveButton"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="save this Data"
android:textSize="20sp" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="20dp"
android:padding="20dp"
android:orientation="vertical">
<TextView
android:gravity="center"
android:hint="~RollNo~"
android:textColor="#color/colorPrimary"
android:id="#+id/display_rollno"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="30sp" />
<TextView
android:layout_marginTop="20dp"
android:id="#+id/display_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:hint="~Name~"
android:textColor="#color/colorPrimary"
android:textSize="30sp" />
</LinearLayout>
</LinearLayout>
In MainActivity :
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private static final String KEY_ROLL = "rollno_key";
private static final String KEY_NAME = "name_key";
int rollno;
String name;
EditText roll_et , name_et;
TextView roll_tv , name_tv;
Button saveButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
roll_et = (EditText) findViewById(R.id.rollnoID_edit);
name_et = (EditText) findViewById(R.id.nameID_edit);
roll_tv = (TextView) findViewById(R.id.display_rollno);
name_tv = (TextView) findViewById(R.id.display_name);
if (savedInstanceState != null){
String save_RollNO = savedInstanceState.getString(KEY_ROLL);
roll_tv.setText(save_RollNO);
String save_Name = savedInstanceState.getString(KEY_NAME);
name_tv.setText(save_Name);
} else {
Toast.makeText(getApplicationContext(),"Entry your data",Toast.LENGTH_SHORT).show();
}
}
#Override
public void onSaveInstanceState(Bundle saveData) {
saveData.putString(KEY_ROLL , roll_et.getText().toString());
saveData.putString(KEY_NAME , name_et.getText().toString());
super.onSaveInstanceState(saveData);
}
public void saveData(View v){
roll_tv.setText(roll_et.getText().toString().trim());
name_tv.setText(name_et.getText().toString().trim());
}
}

Text view doesn't show after button click - Android

I have a problem with Text View and Button in Android Studio. I would like to update my text view when i clik a button but it doesn't work.
This is my code:
activity_distance_to_run.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
tools:layout_editor_absoluteY="25dp">
<TextView
android:id="#+id/Distancerun2"
android:layout_width="126dp"
android:layout_height="50dp"
android:layout_marginTop="50dp"
android:text="Distance to ....."
android:textSize="14sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/distancetorun"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="10dp"
android:layout_marginRight="10dp"
android:text="run"
app:layout_constraintBaseline_toBaselineOf="#+id/distancetoride"
app:layout_constraintEnd_toStartOf="#+id/distancetoride"
app:layout_constraintStart_toStartOf="parent" />
<Button
android:id="#+id/distancetoride"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="9dp"
android:layout_marginRight="9dp"
android:layout_marginTop="32dp"
android:text="ride a bicycle"
app:layout_constraintEnd_toStartOf="#+id/distancetoswim"
app:layout_constraintStart_toEndOf="#+id/distancetorun"
app:layout_constraintTop_toBottomOf="#+id/Distancerun2" />
<Button
android:id="#+id/distancetoswim"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="swim"
app:layout_constraintBaseline_toBaselineOf="#+id/distancetoride"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="#+id/distancetoride" />
<Button
android:id="#+id/yes"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="32dp"
android:layout_marginStart="32dp"
android:text="I did it !!"
app:layout_constraintBaseline_toBaselineOf="#+id/no"
app:layout_constraintStart_toStartOf="parent" />
<Button
android:id="#+id/no"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="116dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:text="I don't want to do it !!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView1" />
<TextView
android:id="#+id/textView1"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="23dp"
android:layout_marginEnd="25dp"
android:layout_marginLeft="25dp"
android:layout_marginRight="25dp"
android:layout_marginStart="25dp"
android:layout_marginTop="221dp"
android:autoText="true"
android:clickable="true"
android:enabled="false"
android:freezesText="false"
android:text="Elo ziomek"
android:textSize="24sp"
app:layout_constraintBottom_toTopOf="#+id/no"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
distancetorun.java
package pl.agcode.sqliteexample;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class distance_to_run extends Activity {
Button distancetorun;
TextView txtView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_distance_to_run);
distancetorun = (Button) findViewById(R.id.distancetorun);
txtView = (TextView) findViewById(R.id.textView1);
distancetorun.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
txtView.setText("NewText");
}
});
}
}
Thanks for help I will try to repair it but don't know how.
This is very important to repair this for me. :)

Looks all good except textview1 color.
Add below line for the textview1 in layout xml
<TextView
android:id="#+id/textView1"
android:textColor="#android:color/black"
After launching the app
After clicking RUN button

java.lang.NullPointerException: Attempt to invoke virtual method 'setOnClickListener' on a 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.
I may have some troubles finding where the problem is ... Here is my activity_main.xml :
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:orientation="vertical"
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.grasland.test.MainActivity">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/poids"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:text="#string/poids"
android:textColor="#FF0000"
android:textStyle="bold"
android:textSize="20sp" />
<EditText
android:id="#+id/editPoids"
android:layout_width="match_parent"
android:layout_height="50sp"
android:layout_below="#id/poids"
android:hint="#string/editPoids"
android:inputType="number"/>
<TextView
android:id="#+id/taille"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/editPoids"
android:layout_centerHorizontal="true"
android:text="#string/taille"
android:textColor="#FF0000"
android:textStyle="bold"
android:textSize="20sp" />
<EditText
android:id="#+id/editTaille"
android:layout_width="match_parent"
android:layout_height="50sp"
android:layout_below="#id/taille"
android:hint="#string/editTaille"
android:inputType="number"/>
<RadioGroup
android:id="#+id/radioGroup1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:orientation="horizontal"
android:layout_below="#id/editTaille">
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/radioButtonCm"
android:checked="true" />
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/radioButtonM"/>
</RadioGroup>
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_below="#id/radioGroup1"
android:text="#string/button"/>
<TextView
android:id="#+id/resultTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/button"
android:paddingTop="40dp"
android:layout_centerHorizontal="true"
android:text="#string/resultTitle"
android:textSize="20sp" />
<TextView
android:id="#+id/result"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/resultTitle"
android:paddingTop="20dp"
android:layout_centerHorizontal="true"
android:textSize="80sp" />
</RelativeLayout>
</FrameLayout>
and there is my java file :
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Button calculImc = (Button) findViewById(R.id.button);
final EditText poidsView = (EditText) findViewById(R.id.editPoids);
final EditText tailleView = (EditText) findViewById(R.id.editTaille);
final TextView resultat = (TextView) findViewById(R.id.result);
calculImc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
int iPoids = Integer.parseInt(poidsView.getText().toString());
int iTaille = Integer.parseInt(tailleView.getText().toString());
double dResult = iPoids / ( ( iTaille * iTaille ) / 1000 );
resultat.setText(Double.toString(dResult));
}
});
}
}
I can't see the reason for this NullPointerException I'm getting (I may be a bit tired ...).
Thanks in advance !
Sylvain.

I don't see you placing the setContentView function below onCreate
You should consider doing:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
...
}

Android button click doesn't work and editing textbox with it

I'm really new in coding for Android, just started to learn. I have some image buttons to change values displayed in textboxes and I don't know how to do this. I tried some tests for buttons but I have some errors which I can't repair.
Message from eclipse is:
The method setOnClickListener(View.OnClickListener) in the type View is not applicable for the arguments (new OnClickListener(){})
and
The method setOnClickListener(View.OnClickListener) in the type View is not applicable for the arguments (new OnClickListener(){})
for setOnClickListener and OnClickListener
I looked at this thread but still I don't know what to do
setOnClickListener(View.OnClickListener) in the type View is not applicable for the arguments (SequencerActivity) back.setOnClickListener(this);
Except that, I want to change the Medium text fields with the buttons. Perhaps by the declared integers.
Code:
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends Activity {
Button b1;
Button b2;
Button b3;
Button b4;
Button b5;
Button b6;
Button b7;
Button b8;
int vs,vh,ws,wh,wth,wts;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1=(Button) findViewById(R.id.imageButton1);
b1.setOnClickListener(new OnClickListener()
{
protected void onClick(View v)
{
Toast.makeText(ApplicationContext(), "Om nom nom", Toast.LENGTH_SHORT).show();
}
});
}
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:background="#012e53"
android:paddingBottom="5dp"
android:paddingLeft="5dp"
android:paddingRight="5dp"
android:paddingTop="5dp"
tools:context="pl.tmalachowski.truewindcalc.MainActivity" >
<TabWidget
android:id="#android:id/tabs"
android:layout_width="wrap_content"
android:layout_height="wrap_content" >
<ScrollView
android:id="#+id/scrollView1"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="26dp"
android:orientation="horizontal" >
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.5"
android:gravity="center"
android:orientation="vertical"
android:textColor="#bdc3c7" >
<TextView
android:id="#+id/textView9"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/ves"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/podst" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.5"
android:gravity="center" >
<TextView
android:id="#+id/textView10"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/rel"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/podst" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="40dp"
android:orientation="horizontal" >
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:gravity="center" >
<TextView
android:id="#+id/textView1"
android:layout_width="62dp"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/ves1"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/podst" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:gravity="center" >
<TextView
android:id="#+id/textView2"
android:layout_width="77dp"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/ves2"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/podst" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:gravity="center" >
<TextView
android:id="#+id/textView3"
android:layout_width="80dp"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/rel1"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/podst" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:gravity="center" >
<TextView
android:id="#+id/textView4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/rel2"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/podst" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:gravity="center"
android:orientation="horizontal" >
<ImageButton
android:id="#+id/imageButton1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#android:drawable/arrow_up_float" />
</LinearLayout>

I think you are using your onClickListener wrong.
b1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(), "Om nom nom", Toast.LENGTH_SHORT).show();
}
});
Please try this usage. Hope it helps

Declare like this ImageButton b1; instead of Button b1;
then change to like this following code
b1=(ImageButton) findViewById(R.id.imageButton1);
b1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(ApplicationContext(), "Om nom nom", Toast.LENGTH_SHORT).show();
}
});

Android NullPointer Exception in Activity's onCreate

I have a simple application to multiply two numbers from text boxes and display result in third box. There is no any syntax errors in the code but when I am running an application i get this error: application has stopped unexpectedly.
Here is the java code:
package c.example.rectangle;
import android.os.Bundle;
import android.view.View;
import android.app.Activity;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener{
EditText l = (EditText) findViewById(R.id.length);
EditText w = (EditText) findViewById(R.id.width);
TextView a = (TextView) findViewById(R.id.lblarea);
Button b = (Button) findViewById(R.id.calculate);
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b.setOnClickListener(this);
}
public void onClick(View v) {
calculateRectangle(l.getText().toString(), w.getText().toString());
}
private void calculateRectangle(String clength, String cwidth){
int area = Integer.parseInt(clength)*Integer.parseInt(cwidth);
b.setText(String.valueOf(area));
}}
And here is my XML file.
<?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:background="#8B4513"
android:orientation="vertical" >
<TextView
android:id="#+id/label1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dp"
android:background="#2F4F4F"
android:gravity="center"
android:text="#string/rect"
android:textAppearance="?android:attr/textAppearanceMedium" />
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#8B4513"
android:orientation="horizontal" >
<TextView
android:id="#+id/label2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="30dp"
android:layout_marginTop="50dp"
android:background="#2F4F4F"
android:gravity="center"
android:text="#string/cm"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/length"
android:layout_width="110dp"
android:layout_height="21dp"
android:layout_marginLeft="40dp"
android:layout_marginTop="50dp"
android:background="#2F4F4F"
android:ems="10"
android:gravity="center"
android:inputType="number" />
</LinearLayout>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#8B4513"
android:orientation="horizontal" >
<TextView
android:id="#+id/label3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#2F4F4F"
android:layout_marginLeft="30dp"
android:layout_marginTop="20dp"
android:text="#string/breadth"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/width"
android:layout_width="110dp"
android:layout_height="21dp"
android:layout_marginLeft="33dp"
android:layout_marginTop="20dp"
android:background="#2F4F4F"
android:inputType="number"
android:ems="10"
android:gravity="center"
>
<requestFocus />
</EditText>
</LinearLayout>
<Button
android:id="#+id/calculate"
android:layout_width="fill_parent"
android:layout_marginLeft="100dip"
android:layout_marginRight="100dip"
android:layout_height="wrap_content"
android:text="#string/calculate"
android:layout_marginTop="20dp" />
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#8B4513"
android:orientation="horizontal" >
<TextView
android:id="#+id/label4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="30dp"
android:layout_marginTop="20dp"
android:background="#2F4F4F"
android:text="#string/area"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="#+id/lblarea"
android:layout_width="110dp"
android:layout_height="21dp"
android:layout_marginLeft="60dp"
android:layout_marginTop="20dp"
android:background="#2F4F4F"
android:gravity="center"/>
</LinearLayout>
</LinearLayout>
Please help.

I know, that you got correct answer, but I just want to explain you why you need to write code as #Mr.Me says.
You describe your View elements in start of class, and trying to initialize them there. It is not correct. Because you have not attached layout file to activity at the moment when constructor will run your initialization of Views objects. As you can see, you are using findViewById() method, but before use it you should call setContentView().
For better understanding, read Activity Lifecycle, pay attention to rendering proccess.

Rearrange your code to look like this:
EditText l;
EditText w;
TextView a;
Button b;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
l = (EditText) findViewById(R.id.length);
w = (EditText) findViewById(R.id.width);
a = (TextView) findViewById(R.id.lblarea);
b = (Button) findViewById(R.id.calculate);