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Android

Studio

Tutorial

Calculator Par t 1: Simple Calculations


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Intro:

In this Tutorial we are going to start a new project Calculator.

First of all, to start with we are going to create a simple calculator to do simple arithmetic operations (i.e., oneoperator and two operands).

Step 1:

Start Android Studio .Create a new Project .

Application Name : ‘Calculus’ or anything you like

Target Android devices >>

Check Phone and Tablet

Minimum SDK – Android 2.3 Gingerbread

Select a Blank Activity >>

Click Finish keeping the default settings for Activity (Name: Main Activity…..).


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Step 2: Setting Up Layout

Skip to XML Code

First of all insert a Linear Layout (Vertical ) inside the Relative Layout. (Delete the Hello World).

Next Insert a Text Field inside the Linear Layout (Vertical ).

Change the following settings for the Text Field in the XML tab.

Now go back to Design tab insert a Table Layout below the Text Field ‘txtScreen’ .

Now insert a Table Row inside the Table Layout


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Change its settings in XML/Text tab

Go to Design Tab and insert Buttons for operators in the first row.

Insert a new Table Row below the first one and add Buttons to it to finish the Layout.


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Apply the same settings to all the Table Rows

Change the id-s for all Buttons according to this Table:

Button Button Id

Button 0 btn0

Button 1 btn1

Button 2 btn2

Button 3 btn3

Button 4 btn4

Button 5 btn5

Button 6 btn6

Button 7 btn7

Button 8 btn8

Button 9 btn9

Button + btnAdd

Button - btnSubtract

Button * btnMultiply

Button / btnDivide

Button C btnClear

Button . btnDot

For Equals Button apply the following settings


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The final xml code will be:


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android:layout_height="wrap_content" android:text="*" android:id ="@+id/btnMultiply" />


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android:layout_height="wrap_content" android:text="=" android:id ="@+id/btnEquals" android:layout_span="4" />


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Step 3: Setting Up Java

Delete the onCreateOptionsMenu and onOptionsItemSelected functions. We don’t need them…

package com.blogspot.shuttereditz.calculus;

import android.support.v7.app.ActionBarActivity;

import android.os.Bundle;

public class MainActivity extends ActionBarActivity {

@Override

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

}

Below - public class MainActivity extends ActionBarActivity – Insert the code:

private EditText Scr;

private float NumberBf =0, NumAf, result=0;

private String Operation, mod= "replace";

Inside the onCreate() function below the setContentView(R.layout.activity_main); Add the following

code:-

Scr = (EditText) findViewById(R.id.txtScreen); Scr.setText("");

To add functions to the Buttons create an Array of Id’s by inserting this code below:

int idList[] = {R.id.btn0 , R.id.btn1, R.id.btn2 , R.id.btn2 , R.id.btn3 , R.id.btn4, R.id.btn5 , R.id.btn6 , R.id.btn7 , R.id.btn8 , R.id.btn9 ,

R.id.btnAdd , R.id.btnSubtract, R.id.btnMultiply , R.id.btnDivide,

R.id.btnClear ,R.id.btnEquals, R.id.btnDot};


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Now set the Onclick functions to these Buttons:

for(int id:idList) {

View v = (View) findViewById(id);

v.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

onButtonClick(v); }

}); }

Below the OnCreate() function create a new function onButtonClick();

public void onButtonClick(View v) { switch (v.getId()) {

case R.id.btnClear : //ClearScr.setText(""); NumberBf = 0; Operation = "";

break;

case R.id.btnAdd :

mMath("+");

break;

case R.id.btnSubtract:

if(mod.equals("replace")) { String numb = ((Button) v).getText().toString();

getKeyboard(numb);

} else mMath("-");

break;

case R.id.btnMultiply :

mMath("*"); break;

case R.id.btnDivide:

mMath("/"); break;

case R.id.btnEquals: mResult();

Operation = "";

NumberBf = 0; break;

default:

String numb = ((Button) v).getText().toString(); getKeyboard(numb);

break; }

}


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Now add the following code:

public void getKeyboard(String str) {

String ScrTxt = Scr.getText().toString(); ScrTxt += str;

if( mod .equals("add")) Scr.setText(ScrTxt);

else Scr.setText(str);

mod = "add"; }


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The complete Java Code is:

package com.blogspot.shuttereditz.calculus;

import android.support.v7.app.ActionBarActivity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.Toast;

public class MainActivity extends ActionBarActivity {

private EditText Scr; private float NumberBf=0, NumAf, result=0; private String Operation, mod="replace";

@Override protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);

Scr = (EditText) findViewById(R.id.txtScreen);

Scr.setText("");

int idList[] = {R.id.btn0 , R.id.btn1, R.id.btn2 , R.id.btn2 , R.id.btn3 , R.id.btn4,

R.id.btn5 , R.id.btn6 , R.id.btn7 , R.id.btn8 , R.id.btn9 , R.id.btnAdd , R.id.btnSubtract, R.id.btnMultiply , R.id.btnDivide,

R.id.btnClear ,R.id.btnEquals, R.id.btnDot, };

for(int id:idList) { View v = (View) findViewById(id); v.setOnClickListener(new View.OnClickListener() {

@Override public void onClick(View v) {

onButtonClick(v); }

}); }

}

public void mMath(String str) {

mResult();

try { NumberBf = Float.parseFloat(Scr.getText().toString());

Operation = str; }catch (Exception e) {

Toast.makeText(getApplicationContext(),(CharSequence) e, Toast.LENGTH_SHORT).show(); Scr.setText("SYNTAX ERROR");

mod ="replace";

}


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}

public void mResult() { NumAf = 0;

if(!Scr.getText().toString().trim().isEmpty())

NumAf = Float.parseFloat(Scr.getText().toString()); result = NumAf;

try {

switch (Operation) { case "+":

result = NumAf + NumberBf;

break; case "-":

result = NumberBf - NumAf;

break; case "*":

result = NumAf * NumberBf;

break; case "/":

result = NumberBf / NumAf; break;

default: result = NumAf;

break; }

} catch (Exception e) { e.printStackTrace();

}

Scr.setText(String.valueOf(result));

mod = "replace";

}

public void getKeyboard(String str) { String ScrTxt = Scr.getText().toString(); ScrTxt += str; if(mod.equals("add"))

Scr.setText(ScrTxt);

else Scr.setText(str);

mod = "add";

}

public void onButtonClick(View v) { switch (v.getId()) {

case R.id.btnClear : //Clear

Scr.setText("");

NumberBf = 0; Operation = "";

break;


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case R.id.btnAdd :

mMath("+"); break;

case R.id.btnSubtract: if(mod.equals("replace")) {

String numb = ((Button) v).getText().toString(); getKeyboard(numb);

} else mMath("-");

break;

case R.id.btnMultiply :

mMath("*"); break;

case R.id.btnDivide: mMath("/");

break;

case R.id.btnEquals:

mResult(); Operation = "";

NumberBf = 0;

break;

default: String numb = ((Button) v).getText().toString(); getKeyboard(numb);

break; }

}

}


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Now let’s check it out:

That’s it….. We have completed creating a simple calculator. Thank you for using this tutorial…ENJOY!

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