Android app crashes when dialog box is called

Android app crashes when dialog box is called - java

I'm still learning how to make android apps and I'm practicing using the different controls, like EditText, radio buttons, dialog boxes, etc.
I'm trying to have the user enter some info into the app and then display that info into a dialog box when they press the "save" button. Whenever I press save, the app crashes.
I know it has something to do with my onClick method where I set all the input to strings so they can be written to the dialog box. It seems to happening when I try to convert the data from the spinner, radio button, and toggle button to string. When I comment those out, the dialog box works fine with just the edit text data.
Can anyone see what's wrong?
Java 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.EditText;
import android.widget.ToggleButton;
import android.widget.Spinner;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.ArrayAdapter;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.content.DialogInterface;
import android.app.AlertDialog;
import java.text.DecimalFormat;
import java.util.Calendar;
public class ActMain extends Activity {
//----------------------------------------------------------------
// Variables
//----------------------------------------------------------------
// Declare variables
EditText etAppName;
Spinner spCategory;
RadioGroup rgRating;
RadioButton rbGood;
RadioButton rbFair;
RadioButton rbBad;
ToggleButton tbGooglePlay;
EditText etPrice;
Button btnSave;
//----------------------------------------------------------------
// Activity overrides
//----------------------------------------------------------------
//----------------------------------------------------------------
// onCreate
//----------------------------------------------------------------
#Override
protected void onCreate(Bundle savedInstanceState) {
System.out.println("### DEBUG ### onCreate started at " + currentTime() + ".");
super.onCreate(savedInstanceState);
setContentView(R.layout.laymain);
// Define edit text controls
etAppName = (EditText) findViewById(R.id.etAppName);
etPrice = (EditText) findViewById(R.id.etPrice);
// Define spinner adapter
String[] categories = {"Business", "Comics", "Education", "Finance", "Games", "Music", "News", "Tools", "Travel", "Weather"};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, categories);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Define spinner control
spCategory = (Spinner) findViewById(R.id.spCategory);
spCategory.setAdapter(adapter);
// Define spinner event
spCategory.setOnItemSelectedListener(new OnItemSelectedListener()
{
public void onItemSelected(AdapterView<?> parent,
View view, int position, long id)
{
System.out.println("Spinner: \"" +
parent.getItemAtPosition(position) +
"\" selected.");
}
public void onNothingSelected(AdapterView<?> parent)
{
System.out.println("Spinner: no item selected.");
}
});
// Define save button click event
btnSave = (Button) findViewById(R.id.btnSave);
btnSave.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
AlertDialog.Builder builder = new AlertDialog.Builder(v.getContext());
builder.setTitle("Mobile App Reviewer Message");
String appName = etAppName.getText().toString();
String price = etPrice.getText().toString();
String category = spCategory.getSelectedItem().toString();
int rbCheckedId = rgRating.getCheckedRadioButtonId();
RadioButton rbChecked = (RadioButton) findViewById(rbCheckedId);
String rating = rbChecked.getText().toString();
String onGooglePlay;
if(tbGooglePlay.isChecked())
onGooglePlay = "NO";
else
onGooglePlay = "YES";
builder.setMessage("Application: " + appName +
"\nCategory: " + category+
"\nRating: " + rating +
"\nOn Google Play? " + onGooglePlay +
"\nPrice: $" + price +
"\nSave this data?");
builder.show();
}
});
}
XML Code
<LinearLayout 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" >
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Title rows - Text View
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<TextView
android:text="Software News"
android:textSize="22sp"
android:textStyle="bold"
android:gravity="center"
android:layout_gravity="center"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="0dp"
android:layout_margin="4dp"/>
<TextView
android:text="Mobile App Reviewer"
android:textSize="20sp"
android:textStyle="bold"
android:gravity="center"
android:layout_gravity="center"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="0dp"
android:layout_margin="4dp"/>
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
App info
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
App name - Edit text
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<LinearLayout
android:gravity="left"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Application: "
android:textStyle="bold"
android:textSize="14sp"
android:gravity="left"
android:layout_gravity="top"
android:padding="4dp"
android:layout_margin="4dp" />
<EditText
android:id="#+id/etAppName"
android:textSize="16sp"
android:background="#33CCCC"
android:gravity="left"
android:layout_gravity="left"
android:layout_width="100dp"
android:layout_height="25dp"
android:padding="0dp"
android:layout_margin="4dp" />
</LinearLayout>
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
App Category - Spinner
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<LinearLayout
android:gravity="left"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_margin="6dp" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Category: "
android:textStyle="bold"
android:textSize="14sp"
android:gravity="left"
android:layout_gravity="top"
android:padding="4dp"
android:layout_margin="4dp" />
<Spinner
android:id="#+id/spCategory"
android:layout_width="160dp"
android:layout_height="wrap_content" />
</LinearLayout>
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
App Rating - Radio Buttons
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<LinearLayout
android:gravity="left"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_margin="6dp" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Rating: "
android:textStyle="bold"
android:textSize="14sp"
android:gravity="left"
android:layout_gravity="top"
android:padding="4dp"
android:layout_margin="4dp" />
<RadioGroup
android:id="#+id/rgRating"
android:gravity="left"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<RadioButton
android:id="#+id/rbGood"
android:text="Good"
android:textSize="14sp"
android:textStyle="bold"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onRadioButtonClicked" />
<RadioButton
android:id="#+id/rbFair"
android:text="Fair"
android:textSize="14sp"
android:textStyle="bold"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onRadioButtonClicked" />
<RadioButton
android:id="#+id/rbBad"
android:text="Bad"
android:textSize="14sp"
android:textStyle="bold"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onRadioButtonClicked" />
</RadioGroup>
</LinearLayout>
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On Google Play? - Toggle Button
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<LinearLayout
android:gravity="left"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_margin="6dp" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="On Google Play? "
android:textStyle="bold"
android:textSize="14sp"
android:gravity="left"
android:layout_gravity="top"
android:padding="4dp"
android:layout_margin="4dp" />
<ToggleButton
android:id="#+id/tbGooglePlay"
android:textOn="NO"
android:textOff="YES"
android:textSize="12sp"
android:textStyle="bold"
android:layout_width="75dp"
android:layout_height="wrap_content"/>
</LinearLayout>
<!--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On Google Play? - Toggle Button
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->
<LinearLayout
android:gravity="left"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_margin="6dp" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Price: $ "
android:textStyle="bold"
android:textSize="14sp"
android:gravity="left"
android:layout_gravity="top"
android:padding="4dp"
android:layout_margin="4dp" />
<EditText
android:id="#+id/etPrice"
android:textSize="16sp"
android:background="#33CCCC"
android:inputType="numberDecimal"
android:gravity="left"
android:layout_gravity="left"
android:layout_width="100dp"
android:layout_height="25dp"
android:padding="0dp"
android:layout_margin="4dp" />
</LinearLayout>
<Button
android:id="#+id/btnSave"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="6dp"
android:background="#A0CFEC"
android:gravity="center"
android:padding="4dp"
android:text="Save"
android:textSize="14sp"
android:textStyle="bold" />
</LinearLayout>

rgRating is not assigned to anything. So you will get a nullPointerException when calling getCheckedRadioButtonId.
This would be obvious if you checked the stack trace or debugged the application.
To fix it, assign an ID to rgRating in the XML file and do a
rgRating = findViewById(...)
...before you try to call getCheckedRadioButtonId()

Try this:
AlertDialog dialog = builder.create();
dialog.show();

change this
AlertDialog.Builder builder = new AlertDialog.Builder(v.getContext());
to
AlertDialog.Builder builder = new AlertDialog.Builder(ActMain.this);

So after #DKIT pointed out my error with rgRating, I noticed that I had done the same thing with tbGooglePlay.
In the end, adding these lines of code to the Java file fixed my issue:
rgRating = (RadioGroup) findViewById(R.id.rgRating);
tbGooglePlay = (ToggleButton) findViewById(R.id.tbGooglePlay);

Related

Why my android application has stopped?

My project won't open on my device, it say's "Unfortunately,myApp has stopped".
this is my manifest:
this is my activity java :
package bismillah.project;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.content.Intent;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
public class Project2Activity extends Activity {
public static int a,b,c;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//coding start here!!
//input data
EditText pek=(EditText)findViewById(R.id.editText1);
String value=pek.getText().toString();
final int pekerja=Integer.parseInt(value);
EditText lam=(EditText)findViewById(R.id.editText2);
String value1=lam.getText().toString();
final int lama=Integer.parseInt(value1);
EditText up=(EditText)findViewById(R.id.editText3);
String value2=up.getText().toString();
final int upah=Integer.parseInt(value2);
EditText jum=(EditText)findViewById(R.id.editText4);
String value3=jum.getText().toString();
final int jumlah=Integer.parseInt(value3);
//button proses
Button button1=(Button)findViewById(R.id.Button1);
button1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
Spinner bibit = (Spinner)findViewById(R.id.spinner1);
TextView biaya = (TextView)findViewById(R.id.textView6);
if(bibit.getSelectedItem().toString().equals("Cabai Rp.100")){
a=pekerja*(lama*upah)+(jumlah*100);
biaya.setText("Biaya Rp." + a);
if(bibit.getSelectedItem().toString().equals("Tomat Rp.150")){
a=pekerja*(lama*upah)+(jumlah*150);
biaya.setText("Biaya Rp." + a);
if(bibit.getSelectedItem().toString().equals("Timun Rp.200")){
a=pekerja*(lama*upah)+(jumlah*200);
biaya.setText("Biaya Rp." + a);
}
}
}
}
});
//button reset
Button button2=(Button)findViewById(R.id.Button2);
button2.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
TextView biaya = (TextView)findViewById(R.id.textView6);
EditText pek=(EditText)findViewById(R.id.editText1);
EditText lam=(EditText)findViewById(R.id.editText2);
EditText up=(EditText)findViewById(R.id.editText3);
EditText jum=(EditText)findViewById(R.id.editText4);
pek.setText("");
lam.setText("");
up.setText("");
jum.setText("");
biaya.setText("");
}
});
//button pindah activity
Button button3=(Button)findViewById(R.id.Button3);
button3.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
// TODO Auto-generated method stub
Intent i =new Intent(getApplicationContext(),activity2.class);
startActivity(i);
}
});
}
}
and this is my main.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:background="#color/bg"
android:orientation="vertical" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="10dp"
android:text="#string/hello"
android:textColor="#color/warna"
android:textSize="20dp" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="10dp"
android:text="Jumlah Pekerja :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" >
<requestFocus />
</EditText>
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Lama Kerja :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" />
<TextView
android:id="#+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Upah :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" />
<TextView
android:id="#+id/textView4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Jenis Bibit :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<Spinner
android:id="#+id/spinner1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="15dp"
android:entries="#array/list" />
<TextView
android:id="#+id/textView5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Jumlah Bibit :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText4"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" />
<TextView
android:id="#+id/textView6"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="10dp"
android:text="Large Text"
android:textColor="#color/warna2"
android:textAppearance="?android:attr/textAppearanceLarge" />
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:id="#+id/Button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
android:layout_marginTop="20dp"
android:text="Proses" />
<Button
android:id="#+id/Button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="Reset" />
<Button
android:id="#+id/Button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="Hasil Panen" />
</LinearLayout>
</LinearLayout>

I tried your code and I had to delete some stuff from your XML file because it was creating some bugs. It might be related to me but here's your XML I was able to use:
But please do not change your XML file before trying the solution below. If it still doesn't work, you should consider the elements I removed.
<?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" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="10dp"
android:text="hello"
android:textSize="20dp" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="10dp"
android:text="Jumlah Pekerja :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" >
<requestFocus />
</EditText>
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Lama Kerja :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" />
<TextView
android:id="#+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Upah :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" />
<TextView
android:id="#+id/textView4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Jenis Bibit :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<Spinner
android:id="#+id/spinner1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="15dp" />
<TextView
android:id="#+id/textView5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:text="Jumlah Bibit :"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText4"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" />
<TextView
android:id="#+id/textView6"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="10dp"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge" />
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:id="#+id/Button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
android:layout_marginTop="20dp"
android:text="Proses" />
<Button
android:id="#+id/Button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="Reset" />
<Button
android:id="#+id/Button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="Hasil Panen" />
</LinearLayout>
</LinearLayout>
Next I created your Project2Activity java class and activity2 (pretty much empty since you gave no info about it).
So when trying to run your application you get the following error:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.application.so/com.example.application.so.Project2Activity}: java.lang.NumberFormatException: For input string: ""
and it is at :
at com.example.application.so.Project2Activity.onCreate(Project2Activity.java:24)
now if we consider this lines 23 and 24:
String value=pek.getText().toString(); // line 23
final int pekerja=Integer.parseInt(value); // line 24
The error is that you are trying to read (line 23) your editText Value at the creation of the activity, at that time, your editText is still blank which means value will be equal to "" (empty string).
What you want to do instead is to put your lines from 22 to 33 (the ones below) in a button click event, I tried putting them in your button 1 click event and your app doesn't crash any more:
EditText pek=(EditText)findViewById(R.id.editText1);
String value=pek.getText().toString();
final int pekerja=Integer.parseInt(value);
EditText lam=(EditText)findViewById(R.id.editText2);
String value1=lam.getText().toString();
final int lama=Integer.parseInt(value1);
EditText up=(EditText)findViewById(R.id.editText3);
String value2=up.getText().toString();
final int upah=Integer.parseInt(value2);
EditText jum=(EditText)findViewById(R.id.editText4);
String value3=jum.getText().toString();
final int jumlah=Integer.parseInt(value3);
So to summarize, the problem is that you are extracting empty strings from your editTexts and trying to make integers out of them. Instead try making that all reading and integer extracting process on the click of a button where your really need these inputs. just like get the inputs and the final moment.
You should pay attention to your logcat (error messages), it is quite helpful.
What you can also do is to verify that your editTexts are not empty while trying to extract strings from them and raise exception or Toast if they are empty. Nothing too complicated just something like:
if (value.equals("")):
// editText is empty so do something
You can refer to this link for further understanding of how to know when an editText is empty.

Making android EditText vertical scrollable

I am new to Android development and I have an issue with making Android EditText vertically scroll able. The vertical scrolling of the EditText does not work for me. I followed several posts and resources but none of them worked for me.
I am using the following code sample to enable the vertical scroll ability.
this.detailsEditText.setScroller(new Scroller(this));
this.detailsEditText.setMaxLines(1);
this.detailsEditText.setVerticalScrollBarEnabled(true);
this.detailsEditText.setMovementMethod(new ScrollingMovementMethod());
The following are the activity class and layout resource file, respectively I am using in my app.
CreateAppointmentActivity.java
package lk.iit.appointmentmanagerapp.activities;
import java.sql.Date;
import java.sql.Time;
import lk.iit.appointmentmanagerapp.data.Appointment;
import lk.iit.appointmentmanagerapp.data.DatabaseHandler;
import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.text.method.ScrollingMovementMethod;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Scroller;
public class CreateAppointmentActivity extends Activity {
private EditText titleEditText;
private EditText timeEditText;
private EditText detailsEditText;
private EditText dateEditText;
private Button saveButton;
private Button resetButton;
private final DatabaseHandler handler = new DatabaseHandler(this);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_appointment);
this.titleEditText = (EditText)(this.findViewById(R.id.edit_title));
this.timeEditText = (EditText)(this.findViewById(R.id.edit_time));
this.detailsEditText = (EditText)(this.findViewById(R.id.edit_details));
this.dateEditText = (EditText)(this.findViewById(R.id.edit_date));
this.detailsEditText.setScroller(new Scroller(this));
this.detailsEditText.setMaxLines(1);
this.detailsEditText.setVerticalScrollBarEnabled(true);
this.detailsEditText.setMovementMethod(new ScrollingMovementMethod());
SharedPreferences preferences = getSharedPreferences("date_variables", MODE_PRIVATE);
this.dateEditText.setText(preferences.getInt("Year", 0) + "-" + preferences.getInt("Month", 0) + "-" + preferences.getInt("Day", 0));
this.dateEditText.setEnabled(false);
this.saveButton = (Button)(this.findViewById(R.id.save_new_appointment_button));
this.saveButton.setOnClickListener(new View.OnClickListener() {
#SuppressWarnings("deprecation")
#Override
public void onClick(View v) {
String[] dateComponents = dateEditText.getText().toString().split("-");
String[] timeComponents = timeEditText.getText().toString().split(":");
Appointment appointment = new Appointment();
appointment.setAppointment_title(titleEditText.getText().toString());
appointment.setAppointment_date(new Date(Integer.parseInt(dateComponents[0]), Integer.parseInt(dateComponents[1]), Integer.parseInt(dateComponents[2])));
appointment.setAppointment_time(new Time(Integer.parseInt(timeComponents[0]), Integer.parseInt(timeComponents[1]), Integer.parseInt(timeComponents[2])));
appointment.setAppointment_details(detailsEditText.getText().toString());
boolean inserted = handler.addAppointment(appointment);
//
//
}
});
this.resetButton = (Button)(this.findViewById(R.id.reset_button));
this.resetButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
titleEditText.setText("");
timeEditText.setText("");
detailsEditText.setText("");
dateEditText.setText("");
}
});
}
}
activity_create_appointment.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"
android:background="#color/background"
tools:context="lk.iit.appointmentmanagerapp.activities.CreateAppointmentActivity" >
<TextView
android:id="#+id/create_activity_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/welcome_create"
android:layout_centerHorizontal="true"
android:layout_marginTop="15dip"
android:layout_marginBottom="25dip"
android:textSize="18.5sp"
android:textColor="#ffffff" />
<TextView
android:id="#+id/title_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/create_activity_title"
android:layout_marginTop="15dip"
android:text="#string/title_textview_text"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/edit_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/create_activity_title"
android:layout_marginTop="15dip"
android:layout_toRightOf="#+id/title_textview"
android:layout_marginLeft="30dip"
android:background="#ffffff"
android:ems="10"
android:inputType="text" >
<requestFocus />
</EditText>
<TextView
android:id="#+id/time_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/title_textview"
android:layout_marginTop="25dip"
android:text="#string/time_textview_text"
android:textAppearance="?android:attr/textAppearanceMedium"
/>
<EditText
android:id="#+id/edit_time"
android:background="#ffffff"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="#+id/time_textview"
android:layout_below="#+id/edit_title"
android:layout_marginLeft="25dip"
android:layout_marginTop="25dip"
android:ems="10"
android:inputType="time" />
<TextView
android:id="#+id/details_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/time_textview"
android:text="#string/details_textview_text"
android:layout_marginTop="25dip"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/edit_details"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/details_textview"
android:layout_alignBottom="#+id/details_textview"
android:layout_alignLeft="#+id/edit_title"
android:background="#ffffff"
android:ems="10"
android:inputType="text" >
</EditText>
<TextView
android:id="#+id/date_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/details_textview"
android:text="Date"
android:layout_marginTop="25dip"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/edit_date"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="#+id/date_textview"
android:layout_below="#+id/edit_details"
android:background="#ffffff"
android:layout_marginLeft="25dip"
android:layout_marginTop="25dip"
android:ems="10"
android:inputType="date" >
</EditText>
<Button
android:id="#+id/save_new_appointment_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#+id/date_textview"
android:layout_marginTop="15dip"
android:layout_marginBottom="10dip"
android:layout_centerHorizontal="true"
android:text="#string/save_button_text"
android:textAllCaps="false" />
<Button
android:id="#+id/reset_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#+id/save_new_appointment_button"
android:layout_marginTop="2dip"
android:layout_centerHorizontal="true"
android:text="#string/reset_button_text"
android:textAllCaps="false" />
</RelativeLayout>
Please bear with me if I have done any mistakes as I am relatively new to this area of development.
I would be grateful if someone help me out with this issue.

Try this in java code:
EditText dwEdit = (EditText) findViewById(R.id.DwEdit);
dwEdit.setOnTouchListener(new OnTouchListener() {
public boolean onTouch(View view, MotionEvent event) {
// TODO Auto-generated method stub
if (view.getId() ==R.id.DwEdit) {
view.getParent().requestDisallowInterceptTouchEvent(true);
switch (event.getAction()&MotionEvent.ACTION_MASK){
case MotionEvent.ACTION_UP:
view.getParent().requestDisallowInterceptTouchEvent(false);
break;
}
}
return false;
}
});
And in your xml:
<EditText
android:id="#+id/DwEdit"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:minLines="10"
android:scrollbarStyle="insideInset"
android:scrollbars="vertical"
android:overScrollMode="always"
android:inputType="textCapSentences">
</EditText>

If you wanna scroll editText only in detailEditText then you specify height of editText 50dp or your need and remove inputType="text" from your editText ....it fulfill your need..
and you don't need any code in java relative to that editText..

button_id Cannot be resolved or is not a field

I've been searching about this problem a lot before posting this question but still couldnt get any help,kindly help me in solving this error as im a newbie to this field..!!
Main Java Code
package com.example.firstapp;
import com.example.firstapp.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Button button = (Button) findViewById(R.id.button_id);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(),Second.class);
startActivity(i);
}
});
}
activity_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="com.example.firstapp.MainActivity" >
<EditText
android:id="#+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/imageView1"
android:layout_alignParentBottom="true"
android:layout_marginBottom="26dp"
android:ems="10"
android:inputType="numberPassword" />
<EditText
android:id="#+id/editText5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/editText1"
android:layout_alignLeft="#+id/editText1"
android:ems="10"
android:inputType="textMultiLine"
android:text="Enter your Password"
tools:ignore="HardcodedText" />
<EditText
android:id="#+id/editText3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/editText5"
android:layout_alignLeft="#+id/editText5"
android:layout_marginBottom="20dp"
android:ems="10"
android:inputType="textEmailAddress" >
<requestFocus android:layout_width="wrap_content" />
</EditText>
<EditText
android:id="#+id/editText4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/editText3"
android:layout_alignLeft="#+id/editText3"
android:ems="10"
android:inputType="textMultiLine"
android:text="Enter your E-mail id"
tools:ignore="HardcodedText" />
<ImageView
android:id="#+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/editText4"
android:layout_centerHorizontal="true"
android:layout_marginBottom="36dp"
android:src="#drawable/robo"
android:contentDescription="#null"/>
<EditText
android:id="#+id/editText2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="38dp"
android:ems="10"
android:inputType="textMultiLine"
android:text="Welcome To Foodparkk"
tools:ignore="HardcodedText" />
<Button
android:id="#+id/button_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:text="Login" />
</RelativeLayout>
activity_second.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="com.example.firstapp.Second" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
</RelativeLayout>

As i mentioned in my comments earlier, There is no button with id button_id..
instead you have android:id="#+id/button1" in your xml file..
so, please change
final Button button = (Button) findViewById(R.id.button_id);
to
final Button button = (Button) findViewById(R.id.button1);
in MainActivity.java
OR
change
android:id="#+id/button1"
to
android:id="#+id/button_id"
in your activity_main.xml

The button id that you are trying to reference in your Java code (using R.id.button_id) doesn't match the one you declared in your xml file (android:id="#+id/button1"). Try changing it to button1 and the error should go away.

replace R.id.button_id with R.id.button1 since this is what is present in your xml

Button and image disappear Android

Im taking my first steps in developing for android. Following a tutorial i have created a button, textview,edit text, and am now trying to implimetn a list view.
i have followed the tutorial Exactly, and for some reason, when i implement the Tableview, my button and image disappear.
can anybody find out why?
.java:
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.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends ActionBarActivity implements View.OnClickListener {
TextView mainTextView;
Button mainButton;
EditText mainEditText;
ListView mainListView;
ArrayAdapter mArrayAdapter;
ArrayList mNameList = new ArrayList();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//access the textview defined in Layout XML & set its value
mainTextView = (TextView) findViewById(R.id.main_textview);
mainTextView.setText("set In Java!");
//access the button defined in layout XML
mainButton = (Button) findViewById(R.id.main_button);
mainButton.setOnClickListener(this);
mainEditText = (EditText) findViewById(R.id.main_edittext);
mainListView = (ListView)findViewById(R.id.main_listview);
mArrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1,mNameList);
mainListView.setAdapter(mArrayAdapter);
}
#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);
}
#Override
public void onClick(View v) {
mainTextView.setText(mainEditText.getText().toString() + " is learning Android Development");
mNameList.add(mainEditText.getText().toString());
mArrayAdapter.notifyDataSetChanged();
}
}
activity.XML:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<TextView
android:id="#+id/main_textview"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/textview"/>
<EditText
android:id="#+id/main_edittext"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:hint="#string/hint"/>
<ListView
android:id="#+id/main_listview"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:layout_marginTop="20dp"/>
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<!-- set OnClickListener to trigger results when pressed -->
<Button
android:id="#+id/main_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:text="#string/button"/>
<!--shows an image from your drawable rescources-->
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:layout_marginLeft="20dp"
android:src="#drawable/ic_launcher"/>
</LinearLayout>
</LinearLayout>

Try this way,hope this will help you to solve your problem.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="#+id/main_textview"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/textview"/>
<EditText
android:id="#+id/main_edittext"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:hint="#string/hint"/>
</LinearLayout>
<ListView
android:id="#+id/main_listview"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:layout_marginTop="20dp"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<Button
android:id="#+id/main_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:text="#string/button"/>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:layout_marginLeft="20dp"
android:src="#drawable/ic_launcher"/>
</LinearLayout>
</LinearLayout>

Try this..
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content" >
<TextView
android:id="#+id/main_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:text="textview" />
<EditText
android:id="#+id/main_edittext"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:hint="hint" />
</LinearLayout>
<ListView
android:id="#+id/main_listview"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_marginTop="20dp"
android:layout_weight="1" />
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<!-- set OnClickListener to trigger results when pressed -->
<Button
android:id="#+id/main_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:text="button" />
<!-- shows an image from your drawable rescources -->
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:src="#drawable/ic_launcher" />
</LinearLayout>
</LinearLayout>

LinearLayout is horizontal by default.
Your ListView is layout_width="match_parent" and root LinearLayout is horizontal.
so ListView Expands wide, ImageView and etc have pushed out and become invisible.
I recommend you to always specify android:orientation ("vertical" or "horizontal") in LinearLayout.

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);

We Keep Coding

Java is a programming language and computing platform first released by Sun Microsystems in 1995.

Android app crashes when dialog box is called - java

Try this: AlertDialog dialog = builder.create(); dialog.show();

change this AlertDialog.Builder builder = new AlertDialog.Builder(v.getContext()); to AlertDialog.Builder builder = new AlertDialog.Builder(ActMain.this);

So after #DKIT pointed out my error with rgRating, I noticed that I had done the same thing with tbGooglePlay. In the end, adding these lines of code to the Java file fixed my issue: rgRating = (RadioGroup) findViewById(R.id.rgRating); tbGooglePlay = (ToggleButton) findViewById(R.id.tbGooglePlay);

Related

Why my android application has stopped?

Making android EditText vertical scrollable

button_id Cannot be resolved or is not a field

Button and image disappear Android

Android NullPointer Exception in Activity's onCreate

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