How to send a variable from Activity to Fragment in Android using Kotlin?

This example demonstrates how to send a variable from Activity to Fragment 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"
   android:orientation="vertical"
   android:padding="2dp"
   tools:context=".MainActivity">
   <EditText
      android:id="@+id/editText"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginTop="20sp"
      android:hint="ENTER YOUR MESSAGE" />
   <Button
      android:id="@+id/btnSendData"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Send data" />
   <FrameLayout
      android:id="@+id/frameLayout"
      android:layout_width="match_parent"
      android:layout_height="match_parent">
   </FrameLayout>
</LinearLayout>

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

import android.os.Bundle
import android.widget.Button
import android.widget.EditText
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentTransaction
class MainActivity : AppCompatActivity() {
   lateinit var editText: EditText
   lateinit var button: Button
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      val fragmentManager: FragmentManager = supportFragmentManager
      val fragmentTransaction: FragmentTransaction = fragmentManager.beginTransaction()
      val myFragment = MyFragment()
      button = findViewById(R.id.btnSendData)
      editText = findViewById(R.id.editText)
      button.setOnClickListener {
         val bundle = Bundle()
         bundle.putString("message", editText.text.toString())
         myFragment.arguments = bundle
         fragmentTransaction.add(R.id.frameLayout, myFragment).commit()
      }
   }
}

Step 4 − Create a new Blank Fragment and add the following codes

MyFragment.kt

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.fragment.app.Fragment
class MyFragment : Fragment() {
   private lateinit var textView:TextView
   override fun onCreateView(
      inflater: LayoutInflater, container: ViewGroup?,
      savedInstanceState: Bundle?
   ): View? {
      val view: View = inflater.inflate(R.layout.fragment_my, container, false)
      textView = view.findViewById<View>(R.id.textView) as TextView
      val bundle = arguments
      val message = bundle!!.getString("message")
      textView.text = message
      return view
   }
}

fragment_my.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:gravity="center"
   android:padding="4dp">
   <TextView
      android:id="@+id/textView"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:textColor="@android:color/holo_orange_dark"
      android:textSize="36sp"
      android:textStyle="bold" />
</LinearLayout>

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.