How to Communicate Between Fragments in Android?

Now a day most apps have so many features so for that they use multiple fragments in a single app and communication is one of the important parts of apps for sharing data from one fragment to another because two fragments can’t communicate directly. A Fragment represents a portion of any user interface. There can be a number of fragments within one activity. They have their own life cycle.

Approach

There are multiple ways in which we can communicate within apps:

• We can communicate within fragments using the ViewModel.
• We can also communicate between fragments using Interface.

In this article, we are going to explain communicating within between fragments using the Interface using Kotlin.

Step by Step Implementation

Step 1: Create a New Project in your android studio 

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Kotlin as the programming language.

Step 2: Create two blank fragments 

Navigate to your Project file where MainActivity.kt exists. Right-click on that folder and click on the new package and name it fragments. Now inside this newly created folder create two blank fragments and name them Fragment1 & Fragment2.

Step 3: Working with XML files

Navigate to the app > res > layout > fragment1.xml and add the below code to that file. Below is the code for the fragment1.xml file. 

XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    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"
    tools:context=".fragments.Fragment1">

    <!-- Text View for showing Fragment1 text -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Fragment 1"
        android:textSize="40sp"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:layout_marginTop="20dp"
        android:textColor="@color/black"/>

    <!-- Edit Text for taking user input -->
    <EditText
        android:id="@+id/messageInput"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Enter text to Pass"
        android:layout_marginTop="200dp"
        android:gravity="center"
        android:layout_marginLeft="30dp"
        android:layout_marginRight="30dp"
        android:textSize="30sp"/>

   <!-- Button for submit user response -->
    <Button
        android:id="@+id/sendBtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/etText"
        android:text="Submit"
        android:backgroundTint="#0F9D58"
        android:textSize="20sp"
        android:textAllCaps="false"
        android:layout_marginLeft="30dp"
        android:layout_marginRight="30dp"
        android:layout_marginTop="20dp" />

</RelativeLayout>

Navigate to the app > res > layout > fragment2.xml and add the below code to that file. Below is the code for the fragment2.xml file. 

XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    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"
    tools:context=".fragments.Fragment2">

    <!-- Text View for showing Fragment2 text -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Fragment 2"
        android:textSize="40sp"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:layout_marginTop="20dp"
        android:textColor="@color/black"/>

    <!-- Frame Layout which will replaced by data from Fragment1 -->
    <FrameLayout
        android:id="@+id/frameLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/displayMessage"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Text"
            android:textSize="30sp"
            android:layout_centerHorizontal="true"
            android:gravity="center"
            android:layout_marginTop="300dp"
            android:textColor="@color/black"/>

    </FrameLayout>

</RelativeLayout>

Step 4: Create Interface

Again navigate to your Project folder where MainActivity.kt exists and right-click on that folder -> new -> Kotlin class/file -> Interface them name it as Communicator.

Kotlin

package com.mrtechy.gfg

interface Communicator {
    fun passData(editTextInput:String)
}

Step 5: Working With the MainActivity.kt

Kotlin

package com.mrtechy.gfg

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.mrtechy.gfg.fragments.Fragment1
import com.mrtechy.gfg.fragments.Fragment2

class MainActivity : AppCompatActivity(), Communicator {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // created instance of Fragment1
        val fragment1 = Fragment1()

        // Frame manager called to replace Fragment2 frame layout with Fragment1 data
        supportFragmentManager.beginTransaction().replace(R.id.frameLayout,fragment1).commit()
    }

    // Override function which we
    // have created in our interface
    override fun passData(editTextInput: String) {
        val bundle = Bundle()
        bundle.putString("message", editTextInput)

        val transaction = this.supportFragmentManager.beginTransaction()

        // Created instance of fragment2
        val fragment2 = Fragment2()

        fragment2.arguments = bundle
        transaction.replace(R.id.frameLayout,fragment2)
        transaction.commit()
    }
}

Step 6: Working With Fragment1 & Fragment file

Below is the code for the Fragment1.kt and Fragment2.kt files respectively. 

Kotlin

package com.mrtechy.gfg.fragments

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.EditText
import com.mrtechy.gfg.Communicator
import com.mrtechy.gfg.R

class Fragment1 : Fragment() {

    private lateinit var communicator: Communicator

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        // Inflate the layout for this fragment
        val view = inflater.inflate(R.layout.fragment_1, container, false)

        communicator = activity as Communicator

        // there are button and edittext id which we have saved
        val button:Button = view.findViewById(R.id.sendBtn)
        val textMessage:EditText = view.findViewById(R.id.messageInput)

        // pass data to our interface while
        // button clicked using setOnClickListener
        button.setOnClickListener {
            communicator.passData(textMessage.text.toString())
        }

        return view

    }

}

Kotlin

package com.mrtechy.gfg.fragments

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import com.mrtechy.gfg.R

class Fragment2 : Fragment() {

    // initialised a empty string variable
    var displayMessage:String? =""

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        // Inflate the layout for this fragment
        val view = inflater.inflate(R.layout.fragment_2, container, false)
        val displayM:TextView = view.findViewById(R.id.displayMessage)

        // get text from interface and send
        // to textView present in Fragment2
        displayMessage = arguments?.getString("message")
        displayM.text = displayMessage
        return view
    }

}

Output:

Output