How to Create Calculator Android App by using OnClickListner | Button Click Method

Learn to create Calculator Android App by using OnClickListner on all buttons.. 

Coding is below - 

package com.example.admin.designingcalcyapp;

import android.content.res.Configuration;

import android.net.Uri;

import android.renderscript.Sampler;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import com.google.android.gms.appindexing.Action;

import com.google.android.gms.appindexing.AppIndex;

import com.google.android.gms.appindexing.Thing;

import com.google.android.gms.common.api.GoogleApiClient;



public class MainActivity extends AppCompatActivity {

1.

 Below is Variable Declaration

    private EditText result;

    private EditText newNumber;

    private TextView displayOperation;  

    private Double operand1 = null;

    private String pendingOperation = "=";

    private static final String STATE_PENDING_OPERATION = "PendingOperation";

    private static final String STATE_OPERAND1 = "Operand1";


    @Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

2.

Below is Variable Casting

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

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

    displayOperation = (TextView) findViewById(R.id.operation);       



    Button button0 = (Button) findViewById(R.id.button0);

    Button button1 = (Button) findViewById(R.id.button1);

    Button button2 = (Button) findViewById(R.id.button2);

    Button button3 = (Button) findViewById(R.id.button3);

    Button button4 = (Button) findViewById(R.id.button4);

    Button button5 = (Button) findViewById(R.id.button5);

    Button button6 = (Button) findViewById(R.id.button6);

    Button button7 = (Button) findViewById(R.id.button7);

    Button button8 = (Button) findViewById(R.id.button8);

    Button button9 = (Button) findViewById(R.id.button9);

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

    Button buttonAdd = (Button) findViewById(R.id.buttonAdd);
    Button buttonSub = (Button) findViewById(R.id.buttonSub);
    Button buttonDiv = (Button) findViewById(R.id.buttonDiv);
    Button buttonMult = (Button) findViewById(R.id.buttonMult);
    Button buttonEquals = (Button) findViewById(R.id.buttonEqual);

   3 - a 

  

Below is the Listner method, which is called when any number ie 0 to 9 and button dot is pressed.

  

 View.OnClickListener Listner = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Button b = (Button) v;

                newNumber.append(b.getText().toString()); // whatever number you pressed will shown in edittext number widgets box newNumber..


            }
        };

3 - b

Setting OnClickListner on all numbers and Dot (.)

        button0.setOnClickListener(Listner);
        button1.setOnClickListener(Listner);
        button2.setOnClickListener(Listner);
        button3.setOnClickListener(Listner);
        button4.setOnClickListener(Listner);
        button5.setOnClickListener(Listner);
        button6.setOnClickListener(Listner);
        button7.setOnClickListener(Listner);
        button8.setOnClickListener(Listner);
        button9.setOnClickListener(Listner);
        buttonDot.setOnClickListener(Listner);

 4 - a

Below is the opListner method, which is called when any operator ie +, -, *, /, = is pressed.

  View.OnClickListener opListner = new View.OnClickListener(

        ) {
            @Override
            public void onClick(View v) {

                Button b = (Button) v;
                String op = b.getText().toString();
                String value = newNumber.getText().toString();
                try {
                    Double doubleValue = Double.valueOf(value);
                    performOperation(doubleValue, op);

                } catch (NumberFormatException e) {
                    newNumber.setText("");


                }


                pendingOperation = op;
                displayOperation.setText(pendingOperation);
            }
        };
 

4 - b

Setting OnClickListner on all operators ie on +, -, /, *, =

      

buttonEquals.setOnClickListener(opListner);
buttonAdd.setOnClickListener(opListner);
buttonMult.setOnClickListener(opListner);  
buttonDiv.setOnClickListener(opListner);   
buttonSub.setOnClickListener(opListner);

  5.     

Below is the function for Clear button ( buttonC )

  final Button buttonC = (Button)findViewById(R.id.buttonC);
        buttonC.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                result.setText("");
             newNumber.setText("");
                operand1 = null;
                pendingOperation = "=";


            }
        });

  6.       

Below is the Function for Negative button ( buttonNeg )

Button buttonNeg = (Button)findViewById(R.id.buttonNeg);
  buttonNeg.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
                 String value = newNumber.getText().toString();
                 if (value.length()==0){

                     newNumber.setText("-");
                 }

                 else {
                     try {
                         Double doubleValue = Double.valueOf(value);
                         doubleValue *= -1;
                         newNumber.setText(doubleValue.toString());
                     } catch (NumberFormatException e) {
                           //newNumber was - or .

                         newNumber.setText("");

                     }
                 }
             }
         });


    }
7.

Below are methods used to save data across orientation changes ie,

OnSaveInstanceState(), OnRestoreInstanceState(), OnConfigurationChanged()

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putString(STATE_PENDING_OPERATION, pendingOperation); 
        if (operand1 != null) {
            outState.putDouble(STATE_OPERAND1, operand1);
        }
        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        pendingOperation = savedInstanceState.getString(STATE_PENDING_OPERATION);
        operand1 = savedInstanceState.getDouble(STATE_OPERAND1);
        displayOperation.setText(pendingOperation);
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
    }

8.
    

Below is the performOperation Method which is used to perform various types of operations ( +, /, *, - )

private void performOperation (Double value, String operation){

      if(null == operand1){


          operand1 = value;
                }
              else {

            if (pendingOperation.equals("=")){

           pendingOperation = operation;
            }

                switch (pendingOperation){

                    case  "=":
                    operand1 = value;
                    break;

                    case "/":
                        if (value==0){
                            operand1 = 0.0;
                        }else {
                            operand1/=value;
                        }
                    break;

                    case "*":
                        operand1 *= value;


                    case "-":

                        operand1 -= value;
                        break;

                    case "+":
                        operand1 += value;

                        break;


                }


      }

          result.setText(operand1.toString());
          newNumber.setText("");


}



}