How to Create Android Calculator Application

Build a functional calculator app in Android using Kotlin or Java. Learn to design the UI, handle user input, and perform calculations. Visit rrtutors.com.

Published February 16, 2020

In this post we are going to learn how to build mobile app from scratch, we are going to build a simple android calculator application with Kotlin support

Simple Calculator Application

Let's Start

Step 1: Create New Android Project

Open Android Studio
Go to file menu
Select new
Enter project name
Enter activity name
Keep other default settings
Select Language Kotlin
Click on finish button to create a new android project

Step 2: Add Required Dependencies in app level build.gradle file

implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
implementation 'androidx.appcompat:appcompat:1.0.0-beta01'
implementation 'androidx.core:core-ktx:1.3.0-alpha01'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

Step 3: Updated all resourses files

colors.xml

<resources>
    <color name="colorPrimary">#EC9109</color>
    <color name="colorPrimaryDark">#F50959</color>
    <color name="colorAccent">#9C27B0</color>
    <color name="colorWhite">#ffffff</color>
    <color name="colorBlack">#000000</color>
    <color name="colorAsh">#bbb</color>
    <color name="colorBg">#272927</color>
</resources>

style.xml

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>



<style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />

<style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />

<style name="stylish">
    <item name="android:layout_width">0dp</item>
    <item name="android:layout_height">60dp</item>
    <item name="android:layout_weight">1</item>
    <item name="android:gravity">center</item>
    <item name="android:textColor">@android:color/white</item>
    <item name="android:textSize">30sp</item>
    <item name="android:fontFamily">@font/font_family_ptsans</item>
    <item name="android:background">?attr/selectableItemBackground</item>
</style>

<style name="arithmetic_keys" parent="stylish">
    <item name="android:textColor">@android:color/holo_red_light</item>
</style>

<style name="foto_vertical_views">
    <item name="android:layout_width">0dp</item>
    <item name="android:layout_height">60dp</item>
    <item name="android:layout_weight">0.01</item>
    <item name="android:background">@android:color/black</item>
</style>

<style name="CalculatorTextView">
    <item name="android:layout_width">0dp</item>
    <item name="android:layout_height">0dp</item>
    <item name="android:gravity">center</item>
    <item name="android:textSize">30sp</item>
    <item name="android:fontFamily">@font/font_family_ptsans</item>
    <item name="android:background">?attr/selectableItemBackground</item>
</style>

Step 4: Now Update MainActivity.kt and xml file with below code

MainActivity.kt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.content.Intent
import android.os.Handler



class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val handler = Handler()
        handler.postDelayed({
            val intent = Intent(this@MainActivity, CalculatorActivity::class.java)
            startActivity(intent)
            finish()
        }, 2000)
    }
}

activity_main.xml

<FrameLayout xmlns:android="https://schemas.android.com/apk/res/android"
             xmlns:app="https://schemas.android.com/apk/res-auto"
             xmlns:tools="https://schemas.android.com/tools"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:orientation="vertical"
             android:background="@color/colorBg"
             tools:context=".MainActivity">

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            android:orientation="vertical"
            android:gravity="center"
            android:padding="20dp"
            tools:ignore="UseCompoundDrawables">

        <ImageView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:src="@mipmap/ic_launcher"
                android:contentDescription="@string/app_name"/>

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Simple Calculator"
                android:textColor="@color/colorPrimary"
                android:layout_marginTop="10dp"
                android:textSize="14sp"/>



    </LinearLayout>

</FrameLayout>

Step 5: Create new Activity CalculatorActivity.kt and update below code

CalculatorActivity.kt

import android.content.pm.ActivityInfo
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.method.TextKeyListener.clear
import android.util.Log
import android.view.View
import android.view.Window
import android.view.WindowManager
import androidx.appcompat.app.ActionBar
import kotlinx.android.synthetic.main.activity_calculator.*
import org.mariuszgromada.math.mxparser.Expression



class CalculatorActivity : AppCompatActivity() {
    private val TAG = CalculatorActivity::class.java!!.getSimpleName()
    private val text = ""


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        setContentView(R.layout.activity_calculator)

        result_tv.setText("0");

        key_seven.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x7");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "7");
                carryOutCalculation();
            }

        })

        key_percentage.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (!keys_pressed_tv.getText().toString().toString().equals("")) {
                    if (!containsLastLetter("%"))
                        keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "%");
                    carryOutCalculation();
                }

        }})

        key_close_bracket.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (!keys_pressed_tv.getText().toString().toString().equals("")) {
                    if (!containsLastLetter(")") || !containsLastLetter("("))
                        keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + ")");
                    carryOutCalculation();
                }
        }})
        key_open_bracket.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (keys_pressed_tv.getText().toString().toString().equals("")) {
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "(");
                    return;
                }
                if (!containsLastLetter("+") && !containsLastLetter("-") &&
                    !containsLastLetter("x") && !containsLastLetter("÷")) {
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "x(");
                    return;
                }

                if (!containsLastLetter("(")) {
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "(");
                    return;
                }

            }})

        key_divide_operation.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (!keys_pressed_tv.getText().toString().toString().equals("")) {
                    if (!containsLastLetter("÷"))
                        operatorClicked("÷");
                }   
        }})


        key_eight.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x8");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "8");
                carryOutCalculation();
        }})

        key_nine.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x9");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "9");
                carryOutCalculation();
        }})

        key_multiply_operation.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {

                if (!keys_pressed_tv.getText().toString().toString().equals("")) {
                    if (!containsLastLetter("x"))
                        operatorClicked("x");
                }
        }})

        key_four.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x4");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "4");
                carryOutCalculation();
        }})
        
        key_five.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x5");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "5");
                carryOutCalculation();
        }})
        
        key_six.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x6");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "6");
                carryOutCalculation();
        }})
        
        key_subtract_operation.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (keys_pressed_tv.getText().toString().toString().equals("")) {
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "-");
                    return;
                }
                if (!containsLastLetter("-"))
                    operatorClicked("-");   
        }})
        
         key_one.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x1");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "1");
                carryOutCalculation();
        }})
        
         key_two.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x2");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "2");
                carryOutCalculation();
        }})
        
         key_three.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (containsLastLetter("%"))
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString()+ "x3");
                else
                    keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "3");
                carryOutCalculation();
        }})
        
         key_addition_operation.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (!keys_pressed_tv.getText().toString().toString().equals("")) {
                    if (!containsLastLetter("+"))
                        operatorClicked("+");
                }
        }})
        
        key_zero.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + "0");
                carryOutCalculation();
        }})
         key_delete.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                deleteKeyClicked();
        }})

        key_dot.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                if (!keys_pressed_tv.getText().toString().equals("")) {
                    if (!containsLastLetter(".")) {
                        keys_pressed_tv.setText(keys_pressed_tv.getText().toString() + ".");
                    }
                }
        }})
        
        clear_tv.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                keys_pressed_tv.setText("");
                result_tv.setText("0");
                key_delete.setVisibility(View.VISIBLE);
                clear_tv.setVisibility(View.INVISIBLE);
        }})
        
        
         key_submission_operation.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                carryOutCalculation();
                clear_tv.setVisibility(View.VISIBLE);
                key_delete.setVisibility(View.INVISIBLE);
        }})
        
        
        
        
      }



     fun operatorClicked( operator:String) {
        if (clear_tv.getVisibility() == View.VISIBLE && result_tv.getText().toString().toString() != "Error") {
            keys_pressed_tv.setText(result_tv.getText().toString().toString() + operator);
            key_delete.setVisibility(View.VISIBLE);
            clear_tv.setVisibility(View.GONE);
        } else
            keys_pressed_tv.setText(keys_pressed_tv.getText().toString().toString() + operator);
    }

    
 

        fun containsLastLetter( letter :String):Boolean {
            var text = keys_pressed_tv.getText().toString().toString();
            var last = "";
            if(text.length != 0)
                last = text.substring(text.length - 1);
            return last.equals(letter);
        }
     fun deleteKeyClicked() {
     var   text = keys_pressed_tv.getText().toString().toString();
        if (text.length > 0) {

            var newText = text.substring(0, text.length - 1);

            if (newText.equals("-")) {
                newText = "";
            }

            keys_pressed_tv.setText(newText);

            if (!newText.isEmpty()) {
                var last = newText.substring(newText.length - 1);
            } else {
                result_tv.setText("0");
            }
        }
    }

     fun carryOutCalculation() {
        var expression = keys_pressed_tv.text.toString();


        if (expression.contains("x")) {
            expression = expression.replace("x", "*");
        }

        if (expression.contains("÷")) {
            expression = expression.replace("÷", "/");
        }


        if (expression.contains("(") && !expression.substring(expression.lastIndexOf("("), expression.length).contains(")")) {
            expression += ")";
        }

        Log.d(TAG, expression);

        //Carry out the calculation
        var e1 =  Expression(expression);
        var answer = (e1.calculate()).toString();

        //Format Error
        if (answer.equals("NaN"))
            answer = "Error";

        result_tv.setText(answer);
    }

   
}

activity_calculator.xml

<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="https://schemas.android.com/apk/res/android"
        xmlns:app="https://schemas.android.com/apk/res-auto"
        xmlns:tools="https://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >

    <View
            android:id="@+id/view"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:background="@color/colorBg"
            app:layout_constraintBottom_toTopOf="@+id/scrollView2"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    <TextView
            android:id="@+id/result_tv"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_marginTop="8dp"
            android:layout_weight="2"
            android:fontFamily="@font/font_family_ptsans"
            android:gravity="end|center"
            android:maxLines="1"
            android:padding="8dp"
            android:textColor="@color/colorWhite"
            android:textSize="60sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/toggle_nav"
            tools:text="0" />

    <TextView
            android:id="@+id/keys_pressed_tv"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:fontFamily="@font/font_family_ptsans"
            android:gravity="end|center"
            android:maxLines="1"
            android:padding="8dp"
            android:textColor="@color/colorWhite"
            android:textSize="40sp"
            android:scrollHorizontally="true"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/result_tv"
            tools:text="0" />

    <ScrollView
            android:id="@+id/scrollView2"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:fillViewport="true"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/keys_pressed_tv">

        <androidx.constraintlayout.widget.ConstraintLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent">

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="vertical"
                    app:layout_constraintGuide_percent="0.25" />

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline3"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="vertical"
                    app:layout_constraintGuide_percent="0.75" />

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline2"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="vertical"
                    app:layout_constraintGuide_percent="0.5" />

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline4"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal"
                    app:layout_constraintGuide_percent="0.20" />

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline5"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal"
                    app:layout_constraintGuide_percent="0.40" />

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline6"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal"
                    app:layout_constraintGuide_percent="0.60" />

            <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline7"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal"
                    app:layout_constraintGuide_percent="0.80" />

            <TextView
                    android:id="@+id/key_percentage"
                    style="@style/CalculatorTextView"
                    android:text="%"
                    app:layout_constraintBottom_toTopOf="@+id/guideline4"
                    app:layout_constraintEnd_toStartOf="@+id/guideline"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="parent" />

            <TextView
                    android:id="@+id/key_open_bracket"
                    style="@style/CalculatorTextView"
                    android:text="("
                    app:layout_constraintBottom_toTopOf="@+id/guideline4"
                    app:layout_constraintEnd_toStartOf="@+id/guideline2"
                    app:layout_constraintStart_toStartOf="@+id/guideline"
                    app:layout_constraintTop_toTopOf="parent" />

            <TextView
                    android:id="@+id/key_close_bracket"
                    style="@style/CalculatorTextView"
                    android:text=")"
                    app:layout_constraintBottom_toTopOf="@+id/guideline4"
                    app:layout_constraintEnd_toStartOf="@+id/guideline3"
                    app:layout_constraintStart_toStartOf="@+id/guideline2"
                    app:layout_constraintTop_toTopOf="parent" />

            <TextView
                    android:id="@+id/key_divide_operation"
                    style="@style/CalculatorTextView"
                    android:text="÷"
                    app:layout_constraintBottom_toTopOf="@+id/guideline4"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="@+id/guideline3"
                    app:layout_constraintTop_toTopOf="parent" />

            <TextView
                    android:id="@+id/key_seven"
                    style="@style/CalculatorTextView"
                    android:text="7"
                    app:layout_constraintBottom_toTopOf="@+id/guideline5"
                    app:layout_constraintEnd_toStartOf="@+id/guideline"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="@+id/guideline4" />

            <TextView
                    android:id="@+id/key_eight"
                    style="@style/CalculatorTextView"
                    android:text="8"
                    app:layout_constraintBottom_toTopOf="@+id/guideline5"
                    app:layout_constraintEnd_toStartOf="@+id/guideline2"
                    app:layout_constraintStart_toStartOf="@+id/guideline"
                    app:layout_constraintTop_toTopOf="@+id/guideline4" />

            <TextView
                    android:id="@+id/key_nine"
                    style="@style/CalculatorTextView"
                    android:text="9"
                    app:layout_constraintBottom_toTopOf="@+id/guideline5"
                    app:layout_constraintEnd_toStartOf="@+id/guideline3"
                    app:layout_constraintStart_toStartOf="@+id/guideline2"
                    app:layout_constraintTop_toTopOf="@+id/guideline4" />

            <TextView
                    android:id="@+id/key_multiply_operation"
                    style="@style/CalculatorTextView"
                    android:layout_marginBottom="8dp"
                    android:layout_marginEnd="8dp"
                    android:layout_marginStart="8dp"
                    android:layout_marginTop="8dp"
                    android:text="x"
                    app:layout_constraintBottom_toTopOf="@+id/guideline5"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="@+id/guideline3"
                    app:layout_constraintTop_toTopOf="@+id/guideline4" />

            <TextView
                    android:id="@+id/key_four"
                    style="@style/CalculatorTextView"
                    android:text="4"
                    app:layout_constraintBottom_toTopOf="@+id/guideline6"
                    app:layout_constraintEnd_toStartOf="@+id/guideline"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="@+id/guideline5" />

            <TextView
                    android:id="@+id/key_five"
                    style="@style/CalculatorTextView"
                    android:text="5"
                    app:layout_constraintBottom_toTopOf="@+id/guideline6"
                    app:layout_constraintEnd_toStartOf="@+id/guideline2"
                    app:layout_constraintStart_toStartOf="@+id/guideline"
                    app:layout_constraintTop_toTopOf="@+id/guideline5" />

            <TextView
                    android:id="@+id/key_six"
                    style="@style/CalculatorTextView"
                    android:text="6"
                    app:layout_constraintBottom_toTopOf="@+id/guideline6"
                    app:layout_constraintEnd_toStartOf="@+id/guideline3"
                    app:layout_constraintStart_toStartOf="@+id/guideline2"
                    app:layout_constraintTop_toTopOf="@+id/guideline5" />

            <TextView
                    android:id="@+id/key_subtract_operation"
                    style="@style/CalculatorTextView"
                    android:text="-"
                    app:layout_constraintBottom_toTopOf="@+id/guideline6"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="@+id/guideline3"
                    app:layout_constraintTop_toTopOf="@+id/guideline5" />

            <TextView
                    android:id="@+id/key_one"
                    style="@style/CalculatorTextView"
                    android:text="1"
                    app:layout_constraintBottom_toTopOf="@+id/guideline7"
                    app:layout_constraintEnd_toStartOf="@+id/guideline"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="@+id/guideline6" />

            <TextView
                    android:id="@+id/key_two"
                    style="@style/CalculatorTextView"
                    android:text="2"
                    app:layout_constraintBottom_toTopOf="@+id/guideline7"
                    app:layout_constraintEnd_toStartOf="@+id/guideline2"
                    app:layout_constraintStart_toStartOf="@+id/guideline"
                    app:layout_constraintTop_toTopOf="@+id/guideline6" />

            <TextView
                    android:id="@+id/key_three"
                    style="@style/CalculatorTextView"
                    android:text="3"
                    app:layout_constraintBottom_toTopOf="@+id/guideline7"
                    app:layout_constraintEnd_toStartOf="@+id/guideline3"
                    app:layout_constraintStart_toStartOf="@+id/guideline2"
                    app:layout_constraintTop_toTopOf="@+id/guideline6" />

            <TextView
                    android:id="@+id/key_addition_operation"
                    style="@style/CalculatorTextView"
                    android:text="+"
                    app:layout_constraintBottom_toTopOf="@+id/guideline7"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="@+id/guideline3"
                    app:layout_constraintTop_toTopOf="@+id/guideline6" />

            <TextView
                    android:id="@+id/key_zero"
                    style="@style/CalculatorTextView"
                    android:text="0"
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toStartOf="@+id/guideline"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="@+id/guideline7" />

            <TextView
                    android:id="@+id/key_dot"
                    style="@style/CalculatorTextView"
                    android:text="."
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toStartOf="@+id/guideline2"
                    app:layout_constraintStart_toStartOf="@+id/guideline"
                    app:layout_constraintTop_toTopOf="@+id/guideline7" />

            <TextView
                    android:id="@+id/key_submission_operation"
                    style="@style/CalculatorTextView"
                    android:text="="
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="@+id/guideline3"
                    app:layout_constraintTop_toTopOf="@+id/guideline7" />

            <TextView
                    android:id="@+id/key_delete"
                    style="@style/CalculatorTextView"
                    android:text="?"
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toStartOf="@+id/key_submission_operation"
                    app:layout_constraintStart_toStartOf="@+id/guideline2"
                    app:layout_constraintTop_toBottomOf="@+id/key_three" />

            <TextView
                    android:id="@+id/clear_tv"
                    style="@style/CalculatorTextView"
                    android:text="CLS"
                    android:visibility="invisible"
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toStartOf="@+id/guideline3"
                    app:layout_constraintStart_toStartOf="@+id/key_delete"
                    app:layout_constraintTop_toTopOf="@+id/key_delete" />

        </androidx.constraintlayout.widget.ConstraintLayout>

    </ScrollView>

    <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_begin="20dp" />

    <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_begin="20dp" />

    <ImageView
            android:id="@+id/toggle_nav"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:visibility="invisible"
            android:src="@android:drawable/ic_menu_more"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline9" />

    <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_end="20dp" />

    <ImageView
            android:id="@+id/imageView3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:visibility="invisible"
            android:src="@android:drawable/ic_media_play"
            app:layout_constraintEnd_toStartOf="@+id/guideline10"
            app:layout_constraintTop_toTopOf="@+id/guideline9" />

</androidx.constraintlayout.widget.ConstraintLayout>

How to Create Android Calculator Application

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