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Beginner 20 min Java Full project

Fragments in Android Studio: Create and Switch Fragments (Java)

Learn fragments: reusable pieces of a screen that you can swap in and out. Build an activity that switches between fragments with buttons.

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What you'll learn

Create fragments and their layouts
Add and replace fragments with FragmentManager
Switch fragments with buttons
Understand the fragment lifecycle

Before you start

Android Studio (any recent version)
Basic Java: variables, methods and if/else
An emulator or an Android phone

How it fits together

1MainActivity
2FragmentContainerView
3FirstFragment or SecondFragment
4Back returns to the previous one

Build it step by step

1. Create the project

In Android Studio choose New Project → Empty Views Activity, with Language Java and Minimum SDK API 24.

2. Make room for fragments

In activity_main.xml, add a FragmentContainerView with the ID fragment_container. Fragments appear inside it. Below it, add two buttons: First and Second.

3. Create the first fragment

A fragment is a reusable piece of a screen, with its own layout. Create fragment_first.xml, then a FirstFragment class that extends Fragment and passes the layout to the constructor: super(R.layout.fragment_first). That's the whole class.

4. Create the second fragment

SecondFragment has its own button and counter. Find its views in onViewCreated, the fragment's version of an activity's onCreate.

5. Show the first fragment on launch

In MainActivity.onCreate, use getSupportFragmentManager().beginTransaction() to add the first fragment. Only do this when savedInstanceState is null; after a rotation, Android restores the fragment for you.

6. Swap fragments

When a button is tapped, replace the fragment in the container. addToBackStack(null) remembers the swap, so Back returns to the previous fragment. setCustomAnimations adds a fade.

7. Say "1 time", not "1 times"

The counter uses a plurals resource with one and other forms, read with getQuantityString. Android picks the right form for the number and the language.

8. Run it

Tap Second, tap the button a few times, then press Back to return to the first fragment.

If something goes wrong

Two fragments on top of each other after rotating: only add the first fragment when savedInstanceState == null.
Back closes the app instead of going back: add addToBackStack(null) to the transaction.

What's improved over the video

It uses FragmentContainerView, the layout-constructor shortcut, Back-stack support, fade animations and plurals.

Files affected

Check what to add and what to replace before copying code.

app/src/main/java/com/example/fragments/MainActivity.javaReplace file
app/src/main/res/layout/activity_main.xmlReplace file
app/src/main/java/com/example/fragments/FirstFragment.javaAdd these lines
app/src/main/res/layout/fragment_first.xmlAdd these lines
app/src/main/res/layout/fragment_second.xmlAdd these lines
app/src/main/java/com/example/fragments/Screens.javaAdd these lines
app/src/main/java/com/example/fragments/SecondFragment.javaAdd these lines
app/src/main/res/values/strings.xmlReplace file

Application code

Select a file to see its code and where it belongs.

This code uses package com.example.fragments. Change that first line to your own package, the one at the top of your MainActivity.

Replace fileapp/src/main/java/com/example/fragments/MainActivity.java

Adds the first fragment, and swaps fragments when the buttons are tapped.

MainActivity.java

package com.example.fragments;

import android.os.Bundle;
import android.widget.Button;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;

/** One screen with a container that shows either FirstFragment or SecondFragment. */
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Screens.setUp(this, R.layout.activity_main);

        Button first = findViewById(R.id.btnFirst);
        Button second = findViewById(R.id.btnSecond);
        first.setOnClickListener(v -> show(new FirstFragment()));
        second.setOnClickListener(v -> show(new SecondFragment()));

        // Only add the first fragment on a fresh start. After rotation, Android restores the one on screen.
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .setReorderingAllowed(true)
                    .add(R.id.fragment_container, new FirstFragment())
                    .commit();
        }
    }

    /** Swap the fragment in the container. addToBackStack lets Back return to the previous one. */
    private void show(Fragment fragment) {
        getSupportFragmentManager().beginTransaction()
                .setReorderingAllowed(true)
                .setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out, android.R.anim.fade_in, android.R.anim.fade_out)
                .replace(R.id.fragment_container, fragment)
                .addToBackStack(null)
                .commit();
    }
}

Full source code

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