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application is crashing when pressing button [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
number format exception
(2 answers)
Closed 6 years ago.
Hello everyone i'm new here so this is my first post
I want to build my first android app and that would be a GPA calculator to be exact but every time I press the calculate button the app crashes I use android studio and here is the java code
package com.example.mac.gpacalculator;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
TextView result;
EditText grade1;
EditText grade2;
EditText grade3;
EditText grade4;
EditText grade5;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
result=(TextView) findViewById(R.id.total);
grade1=(EditText)findViewById(R.id.num1);
grade2=(EditText)findViewById(R.id.num2);
grade3=(EditText)findViewById(R.id.num3);
grade4=(EditText)findViewById(R.id.num4);
grade5=(EditText)findViewById(R.id.num5);
final Button calcbtn= (Button) findViewById(R.id.calc);
calcbtn.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View view) {
double c1 = Float.parseFloat(grade1.getText().toString());
c1=convert(String.valueOf(grade1));
double c2 = Float.parseFloat(grade2.getText().toString());
c1=convert(String.valueOf(grade2));
double c3 = Float.parseFloat(grade3.getText().toString());
c1=convert(String.valueOf(grade3));
double c4 = Float.parseFloat(grade4.getText().toString());
c1=convert(String.valueOf(grade4));
double c5 = Float.parseFloat(grade5.getText().toString());
c1=convert(String.valueOf(grade5));
double c6=calculation(c1,c2,c3,c4,c5);
result.setText((int) c6);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
public static double convert(String grade)
{
double a=0.0;
//checking the conditions
if(grade.equalsIgnoreCase("A"))
{
a=4.0;
}
if(grade.equalsIgnoreCase("A-"))
{
a=3.7;
}
if(grade.equalsIgnoreCase("B+"))
{
a=3.3;
}
else if(grade.equalsIgnoreCase("B"))
{
a=3.0;
}
if(grade.equalsIgnoreCase("B-"))
{
a=2.7;
}
if(grade.equalsIgnoreCase("C+"))
{
a=2.3;
}
else if(grade.equalsIgnoreCase("C"))
{
a=2.0;
}
if(grade.equalsIgnoreCase("C-"))
{
a=1.7;
}
if(grade.equalsIgnoreCase("D+"))
{
a=1.3;
}
else if(grade.equalsIgnoreCase("D"))
{
a=1.0;
}
else if(grade.equalsIgnoreCase("F"))
{
a=0.0;
}
return a;
}
public static double calculation(double c1, double c2, double c3, double c4, double c5)
{
double operation;
operation=(c1+c2+c3+c4+c5)/5;//calculating the GPA
return operation;
}
#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);
}
}
and here is the XML
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:id="#+id/content_main"
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"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
tools:context="com.example.mac.gpacalculator.MainActivity"
tools:showIn="#layout/activity_main">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:id="#+id/num4"
android:layout_below="#+id/num3"
android:layout_alignStart="#+id/num3"
android:digits="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"
android:textAlignment="center"
android:hint="Grade"
android:inputType="text" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:id="#+id/num5"
android:layout_below="#+id/num4"
android:layout_alignStart="#+id/num4"
android:digits="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"
android:textAlignment="center"
android:hint="Grade"
android:inputType="text" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:id="#+id/num2"
android:layout_below="#+id/num1"
android:layout_alignStart="#+id/num1"
android:digits="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"
android:textAlignment="center"
android:hint="Grade"
android:inputType="text" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:id="#+id/num3"
android:inputType="text"
android:textAlignment="center"
android:hint="Grade"
android:layout_below="#+id/num2"
android:digits="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"
android:layout_alignStart="#+id/num2" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:id="#+id/num1"
android:hint="Grade"
android:digits="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"
android:textAlignment="center"
android:layout_marginTop="49dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:inputType="text" />
<Button
android:text="CALCULATE"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/calc"
android:layout_marginTop="24dp"
android:layout_below="#+id/num5"
android:layout_centerHorizontal="true"
android:onClick="calculation"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="50dp"
android:id="#+id/total"
android:hint="0"
android:layout_below="#+id/calc"
android:layout_centerHorizontal="true"
android:textSize="50sp" />
</RelativeLayout>
Also where can i learn more about android development can you recommend me some resources like books, websites, etc. that would me much appreciated.
Thanks in advance.
oh sorry I didn't include the error message
FATAL EXCEPTION: main
Process: com.example.mac.gpacalculator, PID: 2327
java.lang.NumberFormatException: empty String
at java.lang.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1071)
at java.lang.Float.parseFloat(Float.java:459)
at com.example.mac.gpacalculator.MainActivity$2.onClick(MainActivity.java:51)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Application terminated.

You have to have Button btn = (Button) findViewById(R.id.button); otherwise you will throw a NullPointerException. Check the android monitor to see if that matches the error there.

You have added android:onClick="calculation" in your XML <Button>tag so define a method called calculation which accepts view in your code ..
or simply use calcbtn.setOnClickListener... in your code and remove android:onClick="calculation" from the button tag
Don't use Both android:onClick="calculation and view.setOnClick.. for a same View..
There is no id called fab in your XML so add a FloatingActionButton and give that id to it or comment FloatingActionButton fab ....});

I see multiple error here:
As answered by #charuka, you have added a method in your button android:onClick="calculation, which couldn't be found by android and causes crash.
you are trying to parse EditText into String, which is not String, here: convert(String.valueOf(grade1));, change it to convert(grade1.getText().toString());

problems with activity layout when back button is pressed

I have this activity with EditViews and button. When the button is pressed I move on to a new activity. the problem is when the back button is pressed. The EditViews are not visible. What is expected is that the views and the text that was entered are visible. Also The buttons that appear are from the second activity and not the first.
<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.ammar.android.dailyjobsiteinspection2.MainActivity1Activity">
<ScrollView
android:layout_width="fill_parent"
android:layout_height="350dp"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:id="#+id/scrollView">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:id="#+id/linearLayout">
<TextView
android:layout_width="fill_parent"
android:layout_height="0dp"
android:text="New Text"
android:id="#+id/textView"
android:layout_gravity="center_horizontal"
android:layout_weight="1"
android:visibility="invisible" />
<EditText
android:layout_width="fill_parent"
android:layout_height="70dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:id="#+id/editText"
android:layout_gravity="center"
android:hint="Inspector ID"
/>
<TextView
android:layout_width="fill_parent"
android:layout_height="0dp"
android:text="New Text"
android:id="#+id/textView2"
android:layout_gravity="center_horizontal"
android:layout_weight="1"
android:visibility="invisible" />
<EditText
android:layout_width="fill_parent"
android:layout_height="70dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:id="#+id/editText2"
android:layout_gravity="center"
android:hint="Site Name" />
<TextView
android:layout_width="fill_parent"
android:layout_height="0dp"
android:text="New Text"
android:id="#+id/textView3"
android:layout_gravity="center_horizontal"
android:visibility="invisible"
android:layout_weight="1" />
<EditText
android:layout_width="fill_parent"
android:layout_height="70dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:id="#+id/editText3"
android:layout_gravity="center"
android:hint="Site Address" />
<Button
android:layout_width="160dp"
android:layout_height="60dp"
android:text="Start"
android:id="#+id/button3"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_gravity="center_horizontal"
android:onClick="start"
android:layout_margin="5dp" />
</LinearLayout>
</ScrollView>
</RelativeLayout>
Here is the Java code:
import android.content.Intent;
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.EditText;
public class MainActivity1Activity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_activity1);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main_activity1, 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);
}
public void start(View view){
EditText editText1 = (EditText) findViewById(R.id.editText);
EditText editText2 = (EditText) findViewById(R.id.editText2);
EditText editText3 = (EditText) findViewById(R.id.editText3);
if(!allFieldsEntered(editText1, editText2, editText3)){
com.ammar.android.dailyjobsiteinspection2.Message.message(this, "All fields must be filled before starting an Audit ");
}else{
Intent intent = new Intent(this, MainActivity11Activity.class);
Bundle bundle = getDataBundle(editText1, editText2, editText3);
intent.putExtras(bundle);
setContentView(R.layout.activity_main_activity11);
startActivity(intent);
}
}
private Bundle getDataBundle(EditText editText1, EditText editText2, EditText editText3) {
Bundle bundle = new Bundle();
bundle.putString(MainActivity.INSPECTORID, editText1.getText().toString());
bundle.putString(MainActivity.SITENAME, editText2.getText().toString());
bundle.putString(MainActivity.SITEADDRESS, editText3.getText().toString());
return bundle;
}
private boolean allFieldsEntered(EditText editText1, EditText editText2, EditText editText3) {
return !(editText1.getText().toString().matches("")
|| editText2.getText().toString().matches("")
|| editText3.getText().toString().matches(""));
}
}
Here is the second activity:
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
android:orientation="vertical"
tools:context="com.ammar.android.dailyjobsiteinspection2.MainActivity11Activity">
<ScrollView
android:layout_width="match_parent"
android:layout_height="0dp"
android:id="#+id/scrollView"
android:layout_gravity="center_horizontal"
android:layout_weight="1">
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/layout"></LinearLayout>
</ScrollView>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="60dp"
android:id="#+id/layout2">
android:layout_gravity="center_horizontal">
<TextView
android:layout_width="0dp"
android:layout_height="fill_parent"
android:text="New Text"
android:id="#+id/textView4"
android:layout_weight="1"
android:visibility="invisible" />
<Button
android:layout_width="160dp"
android:layout_height="fill_parent"
android:text="Save"
android:id="#+id/button4"
android:onClick="save" />
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="New Text"
android:id="#+id/textView5"
android:layout_weight="1"
android:visibility="invisible"/>
<Button
android:layout_width="160dp"
android:layout_height="fill_parent"
android:text="Submit"
android:id="#+id/button5"
android:onClick="submit" />
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="New Text"
android:id="#+id/textView6"
android:layout_weight="1"
android:visibility="invisible"/>
</LinearLayout>
</LinearLayout>
and the Java code:
import android.app.ActionBar;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.graphics.Typeface;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.text.Layout;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity11Activity extends ActionBarActivity {
private ArrayList<RadioGroup> radioGroupArrayList;
private String inspectorId;
private String siteName;
private String siteAddress;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_activity11);
setFields();
setUI();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main_activity11, 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 setFields() {
Intent intentBundle = getIntent(); // get intent
Bundle bundle = intentBundle.getExtras(); // get bundle from intent
inspectorId = bundle.getString(MainActivity.INSPECTORID);
siteName = bundle.getString(MainActivity.SITENAME);
siteAddress = bundle.getString(MainActivity.SITEADDRESS);
}
private void setUI() {
TextView textView;
radioGroupArrayList = new ArrayList<RadioGroup>();
LinearLayout ll = (LinearLayout) this.findViewById(R.id.layout);
int count = 0;
for(int i = 0; i<6; i++){
int id = getResources().getIdentifier("PreStart"+ i, "array" , getPackageName());
String [] questions = getResources().getStringArray(id);
textView = new TextView(this);
textView.setText(questions[0]);
textView.setTextSize(24);
textView.setTypeface(null, Typeface.BOLD);
ll.addView(textView);
TextView textView1;
TextView textView2;
RadioGroup radioGroup;
RadioButton radioButton1;
RadioButton radioButton2;
RadioButton radioButton3;
for (int j = 1; j< questions.length; j++){
textView1 = new TextView(this);
textView1.setText(questions[j]);
textView1.setTextSize(18);
radioGroup = new RadioGroup(this);
radioGroupArrayList.add(radioGroup);
radioButton1 = new RadioButton(this);
radioButton2 = new RadioButton(this);
radioButton3 = new RadioButton(this);
radioButton1.setText("Yes");
radioButton2.setText("No");
radioButton3.setText("NA");
radioButton1.setId(count);
radioButton2.setId(count+1);
radioButton3.setId(count+2);
count = count + 3;
radioGroup.addView(radioButton1);
radioGroup.addView(radioButton2);
radioGroup.addView(radioButton3);
radioButton1.setPadding(20, 20, 100, 20);
radioButton2.setPadding(20, 20, 100, 20);
radioButton3.setPadding(20, 20, 100, 20);
radioGroup.setOrientation(LinearLayout.HORIZONTAL);
textView2 = new TextView(this);
textView2.setVisibility(View.INVISIBLE);
ll.addView(textView1);
ll.addView(radioGroup);
ll.addView(textView2);
}
}
EditText editText = new EditText(this);
editText.setId(R.id.editText11);
editText.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.WRAP_CONTENT));
editText.setHint("Enter Comments Here");
ll.addView(editText);
}
public void save(View view){
AnswerListCreator answerCreator = new AnswerListCreator(radioGroupArrayList);
String[] answerList = answerCreator.getAnswerList();
String commentLog = ((EditText) findViewById(R.id.editText11)).getText().toString();
DBHelper dbHelper = new DBHelper(this);
SQLiteDatabase db = dbHelper.getWritableDatabase();
Site site = new Site(inspectorId, siteName, siteAddress, answerList, commentLog, 0);
dbHelper.insertSite(db, site);
// go back to main
Intent intent = new Intent(this, MainActivity.class);
setContentView(R.layout.activity_main);
startActivity(intent);
db.close();
finish();
}
public void submit(View view) {
AnswerListCreator answerCreator = new AnswerListCreator(radioGroupArrayList);
if (!answerCreator.isComplete()) {
com.ammar.android.dailyjobsiteinspection2.Message.message(this, "All fields must be checked");
} else {
answerCreator = new AnswerListCreator(radioGroupArrayList);
String[] answerList = answerCreator.getAnswerList();
String commentLog = ((EditText) findViewById(R.id.editText11)).getText().toString();
DBHelper dbHelper = new DBHelper(this);
SQLiteDatabase db = dbHelper.getWritableDatabase();
Site site = new Site(inspectorId, siteName, siteAddress, answerList, commentLog, 1);
dbHelper.insertSite(db, site);
// go back to main
Intent intent = new Intent(this, MainActivity.class);
setContentView(R.layout.activity_main);
startActivity(intent);
db.close();
finish();
}
}
}

You are changing first Activity's View before calling StartActivity.
Remove this in MainActivity1Activity:
setContentView(R.layout.activity_main_activity11);
Furthermore, if you want to keep view state in MainActivity1Activity don't start it again. Just call finish() in second activity.

My Application won't start up?

I'm not really sure why my application won't start up, I get no errors and I have no idea what's going on? I'm pretty new to android and this is just a basic calculator, but it keeps crashing every time I start it up.
***************Main Activity.java**********************
package com.example.alex.myapplication;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Something(this);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
*******************Something.java******************
package com.example.alex.myapplication;
import android.app.Activity;
import android.view.View;
import android.widget.EditText;
import android.widget.Button;
public class Something extends Activity {
private Button add,subtract,multiply,devide;
private EditText editA, editB, editC;
private double doubleA,doubleB,doubleC;
public Something(Activity a) {
click();
}
public void click(){
editA = (EditText) findViewById(R.id.editText);
editB = (EditText) findViewById(R.id.editText2);
editC = (EditText) findViewById(R.id.editText3);
doubleA =Double.parseDouble(editA.getText().toString());
doubleB =Double.parseDouble(editB.getText().toString());
add = (Button) findViewById(R.id.add);
subtract = (Button) findViewById(R.id.subtract);
multiply = (Button) findViewById(R.id.multiply);
devide = (Button) findViewById(R.id.devide);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA+doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
subtract.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA-doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
multiply.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA*doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
devide.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA/doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
}
}
******************activity_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: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=".MainActivity"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/idk"
android:textSize="17sp"
android:id="#+id/textView"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="numberDecimal"
android:ems="5"
android:id="#+id/editText"
android:hint="First number"
android:layout_centerVertical="true"
android:layout_alignLeft="#+id/textView"
android:layout_alignStart="#+id/textView" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="numberDecimal"
android:ems="5"
android:id="#+id/editText2"
android:hint="Second number"
android:layout_centerVertical="true"
android:layout_alignRight="#+id/textView"
android:layout_alignEnd="#+id/textView" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Add"
android:id="#+id/add"
android:layout_alignParentBottom="true"
android:layout_alignLeft="#+id/editText"
android:layout_alignStart="#+id/editText"
android:layout_marginBottom="166dp" />
<Button
android:layout_width="100dp"
android:layout_height="50dp"
android:text="Subtract"
android:id="#+id/subtract"
android:layout_alignTop="#+id/multiply"
android:layout_alignLeft="#+id/add"
android:layout_alignStart="#+id/add" />
<Button
android:layout_width="100dp"
android:layout_height="50dp"
android:text="Multiply"
android:id="#+id/multiply"
android:layout_marginTop="58dp"
android:layout_below="#+id/devide"
android:layout_alignRight="#+id/devide"
android:layout_alignEnd="#+id/devide" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Devide"
android:id="#+id/devide"
android:layout_below="#+id/editText"
android:layout_alignLeft="#+id/editText2"
android:layout_alignStart="#+id/editText2" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="20"
android:id="#+id/editText3"
android:layout_below="#+id/textView"
android:hint="Results"
android:layout_centerHorizontal="true"
android:layout_marginTop="62dp" />
</RelativeLayout>

The fact that you have created a constructor for the Something class
public Something(Activity a) {
click();
}
instead of using onCreate() is probably the source of the error.
Something is derived from Activity, in which you have to override onCreate() at the very least, and set the View of your Activity in it. You haven't done that, and instead you have created a constructor for Something which is also not allowed.
The solution to your problem is to replace the constructor with onCreate() and set the View of that Activity using setContentView(). Also, you cannot create an Activity object using
new Something(this);

making toast for validate edit text when i push a button

im tired to try this thing,can help me find out my solution.
I try to validate Edittext if edittext filed empty when i push a button will show a toast message.
this my layout.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: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=".MyActivity"
android:id="#+id/relativeLayout">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Panjang"
android:id="#+id/textView"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_gravity="right|left" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number"
android:ems="20"
android:id="#+id/editTextPanjang"
android:layout_below="#+id/textView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:maxLength="10"
android:hint="Panjang"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Lebar"
android:id="#+id/textView2"
android:layout_below="#+id/editTextPanjang"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_gravity="right|left"
/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number"
android:ems="20"
android:id="#+id/editTextLebar"
android:layout_below="#+id/textView2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:maxLength="10"
android:hint="Lebar"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hitung Luas"
android:id="#+id/buttonHitungLuas"
android:layout_below="#+id/editTextLebar"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:onClick="hitugLuas"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Luas"
android:id="#+id/textView3"
android:layout_below="#id/buttonHitungLuas"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number"
android:ems="20"
android:id="#+id/editTextLuas"
android:layout_below="#id/textView3"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/editTextLuas"
android:id="#+id/buttonClear"
android:text="#string/btn_clear"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="#+id/buttonClear"
android:layout_below="#+id/editTextLuas"
android:id="#+id/buttonExit"
android:text="Exit"
/>
</RelativeLayout>
this my java
package com.example.aan.myfirstapp;
import android.content.Context;
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 MyActivity extends ActionBarActivity {
private EditText edtPanjang;
private EditText edtLebar;
private EditText edtLuas;
private Button btnHitungLuas;
private Button btnClear;
private Button btnExit;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
initUI();
initEvent();
}
private void initUI(){
edtPanjang = (EditText) findViewById(R.id.editTextPanjang);
edtLebar = (EditText) findViewById(R.id.editTextLebar);
edtLuas = (EditText) findViewById(R.id.editTextLuas);
btnHitungLuas = (Button) findViewById(R.id.buttonHitungLuas);
btnClear = (Button) findViewById(R.id.buttonClear);
btnExit = (Button) findViewById(R.id.buttonExit);
}
private void initEvent() {
btnHitungLuas.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
hitungLuas();
}
}
btnClear.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
clearData();
}
});
btnExit.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View paramView) {
MyActivity.this.finish();
}
});
}
private void hitungLuas(){
int panjang = Integer.parseInt(edtPanjang.getText().toString());
int lebar = Integer.parseInt(edtLebar.getText().toString());
int luas = panjang*lebar;
edtLuas.setText(luas+"");
}
private void clearData(){
edtLuas.setText("");
edtLebar.setText("");
edtPanjang.setText("");
}
#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_my, 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);
}
}
Sory for my bad english
log chat when i run the emulator
03-12 09:29:21.784 1710-2323/com.google.process.gapps E/Backup﹕ [LegacyBackupAccountManager] Fail to get legacy transport context.
android.content.pm.PackageManager$NameNotFoundException: Application package com.google.android.backup not found
at android.app.ContextImpl.createPackageContextAsUser(ContextImpl.java:2139)
at android.app.ContextImpl.createPackageContext(ContextImpl.java:2115)
at android.content.ContextWrapper.createPackageContext(ContextWrapper.java:658)
at com.google.android.gms.backup.am.<init>(SourceFile:47)
at com.google.android.gms.backup.a.a(SourceFile:65)
at com.google.android.gms.backup.c.a(SourceFile:39)
at com.google.android.gms.backup.b.a(SourceFile:67)
at com.google.android.gms.backup.b.a(SourceFile:39)
at com.google.android.gms.backup.BackupAccountNotifierService.onHandleIntent(SourceFile:76)
at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:65)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.os.HandlerThread.run(HandlerThread.java:61)

You need to handle onClick of the button in this manner and show a toast if the edittext is empty
if(editText.getText().toString().trim().length()==0){
Toast.makeText(getApplicationContext(), "field is empty",
Toast.LENGTH_LONG).show();
}else{
//your code here
}

If you want to check for empty EditText.. try TextUtils for it.
Example
if (TextUtils.isEmpty(edtText.getText().toString().trim())) {
Toast.makeText(getBaseContext(),
"Empty", Toast.LENGTH_SHORT)
.show();
} else {
Toast.makeText(getBaseContext(),
"Not Empty", Toast.LENGTH_SHORT)
.show();
}

My app has crashed android eclipse?

I get an error when I run my android app on my android device. It says Unfortunately, GuessingGame has stopped. It was running before but ever since I added a EditText to the layout, it has been crashing. Here is my MainActivity.java:
package com.h2ogaming.numberguessinggame;
import java.util.Random;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView textOne = (TextView) findViewById(R.id.textView1);
Button pressMe = (Button) findViewById(R.id.button1);
pressMe.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String randText = "";
// TODO Auto-generated method stub
Random randGen = new Random();
int random = randGen.nextInt(5) + 1;
randText = Integer.toString(random);
textOne.setText(randText);
}
});
}
#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;
}
}
Here is my Activity_Main 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=".MainActivity"
android:background="#2288ee">
<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="79dp"
android:text="#string/guess_text"
android:textColor="#ffffff"
android:textSize="26sp" />
<EditText
android:id="#+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/textView2"
android:layout_centerHorizontal="true"
android:ems="10"
android:inputType="number" >
<requestFocus />
</EditText>
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/editText1"
android:layout_centerHorizontal="true"
android:layout_marginTop="19dp"
android:text="#string/text_view1"
android:textColor="#ffffff"
android:textSize="26sp" />
<Button
android:id="#+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="#+id/textView1"
android:layout_centerHorizontal="true"
android:layout_marginTop="22dp"
android:text="#string/btn_press" />
</RelativeLayout>
Please help me. Thanks!

Change your initialization for components.declare proper all components globally. then initialize it like below code:
public class MainActivity extends Activity {
TextView textOne;
Button pressMe;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textOne = (TextView) findViewById(R.id.textView1);
pressMe = (Button) findViewById(R.id.button1);