how to create calculator app in kotlin android

In this article today learn how to create calculator app in kotlin android lets start learn tutorial.

In this program, you'll learn to make a simple calculator using when expression in Kotlin. This calculator would be able to add, subtract, multiply, and divide two numbers.

Android Programming with Kotlin for Beginners - How to Create a simple Calculator App with Android Studio and Kotlin

Learn the basics of Android Studio and programming with Kotlin.

In this course, you will create a simple calculator app with Android Studio and Kotlin. You will learn basic things about the android frameworks activities, fragments, and views.

Robot planning with Kotlin for Beginners. You can make a simple computer App with Android work and Kotlin. You can learn basic things about the robot model actions, fragments and views. Basic Model View Presenter building, What is the action? What is the fragment? What is the perspective? How to have a Constraint design?

Kotlin is the programming language that was made by the one individual that produced IntelliJ thought and is fully supported by Google as the `` first-class '' word for Android. In its system, Kotlin is very related to Java; is solves these similar topics, it's objective oriented and statically typed. But what's important is that Kotlin has a structure that is cleaner, it brings more features and gets some thoughts coming from practical programming. Swift is the programming word that was produced by Apple. It's the general-purpose, multi-paradigm, compiled programming word that is primarily applied for iOS, macOS, watchOS, tvOS, and Unix. Swift has been developing a lot in the last years, it adopts good scheduling patterns and brings modern features which makes programming simple& adaptable. Writing code is Swift is really interactive and you will quickly make the hold of it.

Follow the full source code how to create calculator app in kotlin android

1.MainActivity.java:

package com.javahelps.ak_kotlincalculator

import android.os.Bundle

import android.support.v7.app.AppCompatActivity

import android.view.View

import android.widget.Button

import android.widget.TextView

import net.objecthunter.exp4j.ExpressionBuilder

class MainActivity : AppCompatActivity() {

// TextView used to display the input and output

lateinit var txtInput: TextView

// Represent whether the lastly pressed key is numeric or not

var lastNumeric: Boolean = false

// Represent that current state is in error or not

var stateError: Boolean = false

// If true, do not allow to add another DOT

var lastDot: Boolean = false

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

setContentView(R.layout.activity_main)

txtInput = findViewById(R.id.txtInput)

}

/**

* Append the Button.text to the TextView

fun onDigit(view: View) {

if (stateError) {

// If current state is Error, replace the error message

txtInput.text = (view as Button).text

stateError = false

} else {

// If not, already there is a valid expression so append to it

txtInput.append((view as Button).text)

}

// Set the flag

lastNumeric = true

}

/**

* Append . to the TextView

fun onDecimalPoint(view: View) {

if (lastNumeric && !stateError && !lastDot) {

txtInput.append(".")

lastNumeric = false

lastDot = true

}

/**

* Append +,-,*,/ operators to the TextView

fun onOperator(view: View) {

if (lastNumeric && !stateError) {

txtInput.append((view as Button).text)

lastNumeric = false

lastDot = false // Reset the DOT flag

}

/**

* Clear the TextView

fun onClear(view: View) {

this.txtInput.text = ""

lastNumeric = false

stateError = false

lastDot = false

}

/**

* Calculate the output using Exp4j

fun onEqual(view: View) {

// If the current state is error, nothing to do.

// If the last input is a number only, solution can be found.

if (lastNumeric && !stateError) {

// Read the expression

val txt = txtInput.text.toString()

// Create an Expression (A class from exp4j library)

val expression = ExpressionBuilder(txt).build()

try {

// Calculate the result and display

val result = expression.evaluate()

txtInput.text = result.toString()

lastDot = true // Result contains a dot

} catch (ex: ArithmeticException) {

// Display an error message

txtInput.text = "Error"

stateError = true

lastNumeric = false

}

2.activity_main.xml:

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

<android.support.constraint.ConstraintLayout

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

xmlns:tools="http://schemas.android.com/tools"

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

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingTop="8dp"

tools:context=".MainActivity">

<TextView

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:ems="10"

android:textSize="48sp"

android:background="#efefef"

android:id="@+id/txtInput"

android:gravity="right|center_vertical"

android:maxLength="12"

android:layout_marginLeft="8dp"

android:layout_marginEnd="8dp"

android:layout_marginStart="8dp"

app:layout_constraintTop_toTopOf="parent"

android:layout_marginRight="8dp"/>

<TableLayout

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_marginTop="8dp"

app:layout_goneMarginTop="8dp"

android:layout_marginLeft="8dp"

android:layout_marginBottom="8dp"

android:layout_marginRight="8dp"

app:layout_constraintLeft_toLeftOf="parent"

app:layout_constraintRight_toRightOf="parent"

app:layout_constraintBottom_toBottomOf="parent"

app:layout_constraintTop_toBottomOf="@+id/txtInput"

android:gravity="fill">

<TableRow

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:gravity="center">

<Button

android:text="7"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="8"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="9"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="/"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onOperator"

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

</TableRow>

<TableRow

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:gravity="center">

<Button

android:text="4"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="5"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="6"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="*"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onOperator"

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

</TableRow>

<TableRow

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:gravity="center">

<Button

android:text="1"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="2"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="3"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="-"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onOperator"

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

</TableRow>

<TableRow

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:gravity="center">

<Button

android:text="."

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDecimalPoint"

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

<Button

android:text="0"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onDigit"

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

<Button

android:text="CLR"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onClear"

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

<Button

android:text="+"

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onOperator"

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

</TableRow>

<TableRow

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

<Button

android:text="="

android:background="@drawable/button"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:onClick="onEqual"

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

</TableRow>

</TableLayout>

</android.support.constraint.ConstraintLayout>

3.Create a button.xml file a drawable folder:

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

<shape>

</shape>

</item>

<item>

<shape>

</shape>

</item>

</selector>

4.AndroidManifest.xml:

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

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

package="com.javahelps.ak_kotlincalculator" >

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:roundIcon="@mipmap/ic_launcher_round"

android:supportsRtl="true"

android:theme="@style/AppTheme" >

<intent-filter>

</intent-filter>

</activity>

</application>

</manifest>

5.build gradle:

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {

compileSdkVersion 28

defaultConfig {

applicationId "com.javahelps.kotlincalculator"

minSdkVersion 15

targetSdkVersion 28

versionCode 1

versionName "1.0"

testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

}

buildTypes {

release {

minifyEnabled false

proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

}

dependencies {

implementation fileTree(dir: 'libs', include: ['*.jar'])

implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"

implementation 'com.android.support:appcompat-v7:28.0.0'

implementation 'com.android.support.constraint:constraint-layout:1.1.3'

implementation 'net.objecthunter:exp4j:0.4.8'

testImplementation 'junit:junit:4.12'

androidTestImplementation 'com.android.support.test:runner:1.0.2'

androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

}

Android Tutorial

Wednesday 22 July 2020

how to create calculator app in kotlin android