Fragment to Fragment Communication with Interfaces

In this video we will learn how to send data between two fragments. Since fragments should be modular, reusable components, the communication happens over an interface that the underlying activity implements. This way we can send data from a fragment to an activity and from there to another fragment either by calling a public method or by instantiating a new fragment and sending the values as arguments to it.

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fragment_a.xmlfragment_b.xmlFragmentA.javaFragmentB.javaactivity_main.xmlMainActivity.java

<?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="wrap_content"
    android:background="@android:color/holo_green_light"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button_ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Ok" />

</LinearLayout>

<?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="wrap_content"
    android:background="@android:color/holo_blue_light"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button_ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Ok" />

</LinearLayout>

package com.codinginflow.fragmentcommunicationexample;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;


public class FragmentA extends Fragment {
    private FragmentAListener listener;
    private EditText editText;
    private Button buttonOk;

    public interface FragmentAListener {
        void onInputASent(CharSequence input);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_a, container, false);

        editText = v.findViewById(R.id.edit_text);
        buttonOk = v.findViewById(R.id.button_ok);
        buttonOk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                CharSequence input = editText.getText();
                listener.onInputASent(input);
            }
        });

        return v;
    }

    public void updateEditText(CharSequence newText) {
        editText.setText(newText);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof FragmentAListener) {
            listener = (FragmentAListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement FragmentAListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        listener = null;
    }
}

package com.codinginflow.fragmentcommunicationexample;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;


public class FragmentB extends Fragment {
    private FragmentBListener listener;
    private EditText editText;
    private Button buttonOk;

    public interface FragmentBListener {
        void onInputBSent(CharSequence input);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_b, container, false);

        editText = v.findViewById(R.id.edit_text);
        buttonOk = v.findViewById(R.id.button_ok);
        buttonOk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                CharSequence input = editText.getText();
                listener.onInputBSent(input);
            }
        });

        return v;
    }

    public void updateEditText(CharSequence newText) {
        editText.setText(newText);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof FragmentBListener) {
            listener = (FragmentBListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement FragmentBListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        listener = null;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.codinginflow.fragmentcommunicationexample.MainActivity">

    <FrameLayout
        android:id="@+id/container_a"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <FrameLayout
        android:id="@+id/container_b"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

package com.codinginflow.fragmentcommunicationexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity implements FragmentA.FragmentAListener, FragmentB.FragmentBListener {
    private FragmentA fragmentA;
    private FragmentB fragmentB;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fragmentA = new FragmentA();
        fragmentB = new FragmentB();

        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container_a, fragmentA)
                .replace(R.id.container_b, fragmentB)
                .commit();
    }

    @Override
    public void onInputASent(CharSequence input) {
        fragmentB.updateEditText(input);
    }

    @Override
    public void onInputBSent(CharSequence input) {
        fragmentA.updateEditText(input);
    }
}