How to send data back to the Main Activity in Android using Kotlin?

This example demonstrates how to send data back to the Main Activity in Android using Kotlin

Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:gravity="center_horizontal"    android:orientation="vertical"    tools:context=".MainActivity">    <TextView       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="100dp"       android:layout_marginBottom="50dp"       android:text="Tutorials Point"       android:textAlignment="center"       android:textColor="@android:color/holo_green_dark"       android:textSize="32sp"       android:textStyle="bold" />    <TextView       android:id="@+id/textViewNumbers"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="Numbers: "       android:textColor="@android:color/black"       android:textSize="24sp"       android:textStyle="bold" />    <Button       android:id="@+id/buttonAdd"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="10dp"       android:text="add" />    <Button       android:id="@+id/buttonSubtract"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="5dp"       android:text="subtract" /> </LinearLayout>

Step 3 − Add the following code to src/MainActivity.kt

import android.app.Activity import android.content.Intent import android.os.Bundle import android.widget.Button import android.widget.EditText import android.widget.TextView import android.widget.Toast import androidx.appcompat.app.AppCompatActivity class MainActivity : AppCompatActivity() {    private lateinit var textViewResult: TextView    private lateinit var editTextNumber1: EditText    private lateinit var editTextNumber2: EditText    private lateinit var button: Button    override fun onCreate(savedInstanceState: Bundle?) {       super.onCreate(savedInstanceState)       setContentView(R.layout.activity_main)       title = "KotlinApp"       textViewResult = findViewById(R.id.textViewResult)       editTextNumber1 = findViewById(R.id.editTextNumber1)       editTextNumber2 = findViewById(R.id.editTextNumber2)       button = findViewById(R.id.btnOpenActivity2)       button.setOnClickListener {          if ((editTextNumber1.text.toString() == "" || editTextNumber2.text.toString() == "")) {             Toast.makeText(this@MainActivity, "Please insert numbers", Toast.LENGTH_SHORT).show()          } else {             val number1 = Integer.parseInt(editTextNumber1.text.toString())             val number2 = Integer.parseInt(editTextNumber2.text.toString())             val intent = Intent(this@MainActivity, SecondActivity::class.java)             intent.putExtra("number1", number1)             intent.putExtra("number2", number2)             startActivityForResult(intent, 1)          }       }    }    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {       super.onActivityResult(requestCode, resultCode, data)       if (requestCode == 1) {          if (resultCode == Activity.RESULT_OK) {             val result = data!!.getIntExtra("result", 0)             textViewResult.text = "" + result          }          if (resultCode == Activity.RESULT_CANCELED) {             textViewResult.text = "Nothing selected"          }       }    } }

Step 4 − Create a new activity and add the following code −

activity_second.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:gravity="center_horizontal"    android:orientation="vertical"    tools:context=".MainActivity">    <TextView       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="100dp"       android:layout_marginBottom="50dp"       android:text="Tutorials Point"       android:textAlignment="center"       android:textColor="@android:color/holo_green_dark"       android:textSize="32sp"       android:textStyle="bold" />    <TextView       android:id="@+id/textViewNumbers"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="Numbers: "       android:textColor="@android:color/black"       android:textSize="24sp"       android:textStyle="bold" />    <Button       android:id="@+id/buttonAdd"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="10dp"       android:text="add" />    <Button       android:id="@+id/buttonSubtract"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="5dp"       android:text="subtract" /> </LinearLayout>

SecondActivity.kt

import android.app.Activity import android.content.Intent import android.os.Bundle import android.widget.Button import android.widget.TextView import androidx.appcompat.app.AppCompatActivity class SecondActivity : AppCompatActivity() {    lateinit var textViewNumber: TextView    lateinit var buttonAdd: Button    lateinit var buttonSubtract: Button    override fun onCreate(savedInstanceState: Bundle?) {       super.onCreate(savedInstanceState)       setContentView(R.layout.activity_second)       val intent = intent       val number1 = intent.getIntExtra("number1", 0)       val number2 = intent.getIntExtra("number2", 0)       textViewNumber = findViewById(R.id.textViewNumbers)       textViewNumber.text = "Numbers: $number1, $number2"       buttonAdd = findViewById(R.id.buttonAdd)       buttonSubtract = findViewById(R.id.buttonSubtract)       buttonAdd.setOnClickListener {          val result = number1 + number2          val resultIntent = Intent()          resultIntent.putExtra("result", result)          setResult(Activity.RESULT_OK, resultIntent)          finish()       }       buttonSubtract.setOnClickListener {          val result = number1 - number2          val resultIntent = Intent()          resultIntent.putExtra("result", result)          setResult(Activity.RESULT_OK, resultIntent)          finish()       }    } }

Step 5 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.q11">    <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">       <activity android:name=".MainActivity">          <intent-filter>             <action android:name="android.intent.action.MAIN" />             <category android:name="android.intent.category.LAUNCHER" />          </intent-filter>       </activity>    </application> </manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen