Deeveloping Simple Calculator App in Android

In previous you learned about textview, edittext , buttons and their most commonly used attributes, lets put all these together and develop an Android App which uses all these viws and their attributes.

Demp Application :  “Simple Calculator”

What we will do : We create a layout in which we have user will enter two numbers abd perform “Addition” and “Subtraction” operations.

Our layout will have following views

1: TextView1: to show label “First Number”

2: EditText1: to enter the first number

3: TextView2: to show label “Second Number”

4: EditText: to get the second number

5: Button Add: for Addition

6: Button Subtract: for Subtraction

7: TextView3: to show the answer

When user clicks on ADD or SUBTARCT button we first check that user has entered some number in the edit text and make sure that he/she has not left it blank, if user has left any of the edittext blank we will show a message “Please Enter Both the Numbers”. If user has entered both the numbers , we will perform the operation and show the result in textview3.

Create a new  Android Application named “Calculator” and edit files as below

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.calculator"

    android:versionCode="1"

    android:versionName="1.0" >

    <uses-sdk

        android:minSdkVersion="8"

        android:targetSdkVersion="18" />

    <application

        android:allowBackup="true"

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name"

        android:theme="@style/AppTheme" >

        <activity

            android:name="com.example.calculator.CalculatorMainActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

</manifest>

activity_calculator_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:orientation="vertical" >

   

<!--  TextView for First Number -->

    <TextView

        android:layout_marginTop="30dp"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:textSize="20dp"

        android:textColor="#660033"

        android:layout_marginLeft="5dp"

        android:textStyle="bold"

        android:text="First Number" />

   

<!-- EditText for First Number-->

    <EditText

        android:id="@+id/editTextFirstNumber"

        android:hint="First Number"

        android:layout_marginLeft="10dp"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:inputType="number" >

        <requestFocus />

    </EditText>

   

   

   

<!--  TextView for Second Number -->

    <TextView

        android:layout_marginTop="15dp"

        android:layout_marginLeft="5dp"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:textSize="20dp"

        android:textColor="#660033"

        android:textStyle="bold"

        android:text="Second  Number" />

   

<!-- EditText for Second Number-->

    <EditText

        android:id="@+id/editTextSecondNumber"

        android:layout_marginLeft="10dp"

        android:hint="Second Number"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:inputType="number" />

<!--  TextView to Show Result -->

    <TextView

        android:id="@+id/textViewResult"

        android:layout_marginTop="30dp"

        android:textSize="25dp"

        android:textColor="#0000CC"

        android:textStyle="bold"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center_horizontal"

        android:text="Result" />

   

   

   <LinearLayout

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:layout_marginTop="20dp"

        android:orientation="horizontal" >

       

       <!--  Button for Addition -->

        <Button

            android:id="@+id/buttonAdd"

            android:layout_width="fill_parent"

            android:layout_height="wrap_content"

            android:layout_weight="1"

            android:text="ADD" />

       

         <!--  Button for Subtraction -->

         <Button

            android:id="@+id/buttonSubtract"

            android:layout_width="fill_parent"

            android:layout_height="wrap_content"

            android:layout_weight="1"

            android:text="SUBTRACT" />

    </LinearLayout>

</LinearLayout>

CalculatorMainActivity.java

public class CalculatorMainActivity extends Activity

{

   TextView textViewResult;

   EditText editTextFirstNumber,editTextSecondNumber;

   Button addButton,subtractButton;

                    

   @Override

   protected void onCreate(Bundle savedInstanceState)

   {

       super.onCreate(savedInstanceState);

      setContentView(R.layout.activity_calculator_main);

                                 

      // get the  for refferences of textView, and EditTexts

      textViewResult=(TextView)findViewById(R.id.textViewResult);

      editTextFirstNumber=(EditText)findViewById(R.id.editTextFirstNumber);

      editTextSecondNumber=(EditText)findViewById(R.id.editTextSecondNumber);

                   

      // get the  for refferences of both the buttons

       addButton=(Button)findViewById(R.id.buttonAdd);

       subtractButton=(Button)findViewById(R.id.buttonSubtract);

                   

                   

       // set clickListener on add Button

                   

       addButton.setOnClickListener(new View.OnClickListener() {

                     

        public void onClick(View v)

        {

          // Get the first number entered by user

           String strFirstNumber=editTextFirstNumber.getText().toString();

          // Get the second number entered by user

           String strSecondNumber=editTextSecondNumber.getText().toString();

                          

          /* Check If user has Entered Nothing in either of the Number editText

           *if any of the number contains blank string means user has entered     nothing */

           if(strFirstNumber.equals("")||strSecondNumber.equals(""))

            {

               Toast.makeText(getApplicationContext(), "Please Eneter Both the Numbers", Toast.LENGTH_LONG).show();

               return;

            }

                          

         // Convert both the Number String to Integer

           int firstNumber=Integer.parseInt(strFirstNumber);

           int secondNumber=Integer.parseInt(strSecondNumber);

           // perform addition     

             int  result=firstNumber+secondNumber;

                            

                                        

                           

/* Convert the result to String type because we have to show the             result in String form through textView  */

                     String resultString= String.valueOf(result);

                           

                      // show the result in textViewResult

                      textViewResult.setText("Answer is : "+resultString);

                     }

                });

                 

              //  set clickListener on subtract button Button

                subtractButton.setOnClickListener(new View.OnClickListener() {

                     

                 public void onClick(View v)

                 {

                    // Get the first number entered by user

                     String strFirstNumber=editTextFirstNumber.getText().toString();

                     // Get the second number entered by user

                     String strSecondNumber=editTextSecondNumber.getText().toString();

                          

               /* Check If user has Entered Nothing in either of the Number

editText if any of the number contains blank string means user has  entered nothing */

                   if(strFirstNumber.equals("")||strSecondNumber.equals(""))

                   {

                        Toast.makeText(getApplicationContext(), "Please Eneter Both the Numbers", Toast.LENGTH_LONG).show();

                       return;

                   }

                          

                  // Convert both the Number String to Integer

                  int firstNumber=Integer.parseInt(strFirstNumber);

                  int secondNumber=Integer.parseInt(strSecondNumber);

                       

                   // perform subtraction     

                  int result=firstNumber-secondNumber;

                           

                /* Convert the result to String type because we have to show

                    the result in String form through textView */

                  String resultString= String.valueOf(result);

                           

                  // show the result in textViewResult

                  textViewResult.setText("Answer is : "+resultString);

                 }

              });

                   

         }

                          

}