Android calculator

Project name:SimpleCalculator
Build Target: Android 2.3.3
Application name: SimpleCalculator
Package name: ru.startandroid.develop.simplecalculator
Create Activity: MainActivity

 Open main.xml and draw the screen:

 

 -->>

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

<LinearLayout

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

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent">

    <LinearLayout

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:id="@+id/linearLayout1"

        android:layout_marginLeft="10pt"

        android:layout_marginRight="10pt"

        android:layout_marginTop="3pt">

        <EditText

            android:layout_weight="1"

            android:layout_height="wrap_content"

            android:layout_marginRight="5pt"

            android:id="@+id/etNum1"

            android:layout_width="match_parent"

            android:inputType="numberDecimal">

        </EditText>

        <EditText

            android:layout_height="wrap_content"

            android:layout_weight="1"

            android:layout_marginLeft="5pt"

            android:id="@+id/etNum2"

            android:layout_width="match_parent"

            android:inputType="numberDecimal">

        </EditText>

    </LinearLayout>

    <LinearLayout

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:id="@+id/linearLayout2"

        android:layout_marginTop="3pt"

        android:layout_marginLeft="5pt"

        android:layout_marginRight="5pt">

        <Button

            android:layout_height="wrap_content"

            android:layout_width="match_parent"

            android:layout_weight="1"

            android:text="+"

            android:textSize="8pt"

            android:id="@+id/btnAdd">

        </Button>

        <Button

            android:layout_height="wrap_content"

            android:layout_width="match_parent"

            android:layout_weight="1"

            android:text="-"

            android:textSize="8pt"

            android:id="@+id/btnSub">

        </Button>

        <Button

            android:layout_height="wrap_content"

            android:layout_width="match_parent"

            android:layout_weight="1"

            android:text="*"

            android:textSize="8pt"

            android:id="@+id/btnMult">

        </Button>

        <Button

            android:layout_height="wrap_content"

            android:layout_width="match_parent"

            android:layout_weight="1"

            android:text="/"

            android:textSize="8pt"

            android:id="@+id/btnDiv">

        </Button>

    </LinearLayout>

    <TextView

        android:layout_height="wrap_content"

        android:layout_width="match_parent"

        android:layout_marginLeft="5pt"

        android:layout_marginRight="5pt"

        android:textSize="12pt"

        android:layout_marginTop="3pt"

        android:id="@+id/tvResult"

        android:gravity="center_horizontal">

    </TextView>

</LinearLayout>

Now we need to read field contents, define which buttons has been pressed and output the needed result. Open MainActivity.java and write the code:

public class MainActivity extends Activity implements OnClickListener {

  EditText etNum1;

  EditText etNum2;

  Button btnAdd;

  Button btnSub;

  Button btnMult;

  Button btnDiv;

  TextView tvResult;

  String oper = "";

  /** Called when the activity is first created. */

  @Override

  public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    // find the elements

    etNum1 = (EditText) findViewById(R.id.etNum1);

    etNum2 = (EditText) findViewById(R.id.etNum2);

    btnAdd = (Button) findViewById(R.id.btnAdd);

    btnSub = (Button) findViewById(R.id.btnSub);

    btnMult = (Button) findViewById(R.id.btnMult);

    btnDiv = (Button) findViewById(R.id.btnDiv);

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

    // set a listener

    btnAdd.setOnClickListener(this);

    btnSub.setOnClickListener(this);

    btnMult.setOnClickListener(this);

    btnDiv.setOnClickListener(this);

  }

  @Override

  public void onClick(View v) {

    // TODO Auto-generated method stub

    float num1 = 0;

    float num2 = 0;

    float result = 0;

    // check if the fields are empty

    if (TextUtils.isEmpty(etNum1.getText().toString())

        || TextUtils.isEmpty(etNum2.getText().toString())) {

      return;

    }

    // read EditText and fill variables with numbers

    num1 = Float.parseFloat(etNum1.getText().toString());

    num2 = Float.parseFloat(etNum2.getText().toString());

    // defines the button that has been clicked and performs the corresponding operation

    // write operation into oper, we will use it later for output

    switch (v.getId()) {

    case R.id.btnAdd:

      oper = "+";

      result = num1 + num2;

      break;

    case R.id.btnSub:

      oper = "-";

      result = num1 - num2;

      break;

    case R.id.btnMult:

      oper = "*";

      result = num1 * num2;

      break;

    case R.id.btnDiv:

      oper = "/";

      result = num1 / num2;

      break;

    default:

      break;

    }

    // form the output line

    tvResult.setText(num1 + " " + oper + " " + num2 + " = " + result);

  }

}