Fragments in Android

Introduction

 

A fragment is a reusable UI that is used to provide re-usability and for better management of screen space of a user's device. It was introduced in HONEYCOMB i.e. Android 3.0 (API level 11).

If you need to use fragments for API below 11 you will need to import android-support-v4.jar to your project dependencies.

Fragments can be used in two ways:

1. Direct in XML.
2. Dynamically adding the Fragment using code. This will need a frame layout to add the fragment.

If we use the 1st method we cannot replace the fragment with other fragments but if we dynamically add a fragment we can always replace and make transition animations on the fragment.

Let's start with the application.

1. Create a new project and open the main XML file.

Paste this code into it.

activity_main.xml

<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:padding="10dp"
    android:orientation="vertical"
    >
    <fragment
       class="com.example.articlefragments.Fragment1"
       android:id="@+id/fragment1"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_marginBottom="40dp"/>
    <Button
        android:id="@+id/switchFragmentsButton"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:layout_gravity="center"
        android:layout_marginBottom="10dp"
        android:text="Switch Fragments"/>
    <FrameLayout
        android:id="@+id/frameForDynamicFragments"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </FrameLayout>
</LinearLayout>

The <fragment> tag is the static fragment. We cannot replace this fragment with another fragment. We have also added a FrameLayout to hold another fragment. You will see its use later.

2. Now create 3 XML files named fragment1.xml, fragment2.xml and fragment3.xml

fragment1.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:background="#ABABAB">
    <TextView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:text="This is Static Fragment 1"
        android:textSize="20sp"
        />
</LinearLayout>

fragment2.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:background="#A1A1A1" >
    <TextView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:text="This is text for fragment 2"
        android:textSize="20sp"
        android:gravity="center"
        />
</LinearLayout>

fragment3.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:background="#D1D1D1">
    <TextView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:text="This is text for fragment 3"
        android:textSize="20sp"
        android:gravity="center"
        />
</LinearLayout>

3. Now create 3 Java files Fragment1.java, Fragment2.java, and Fragment3.java.

Fragment1.java

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class Fragment1 extends Fragment{

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub

        View view = inflater.inflate(R.layout.fragment1, container, false);

        return view;
    }
}

Here we have extended the Fragment class from the android.support.v4.app package and overriden the method onCreateView that returns the view for the fragment.
The three files are nearly the same, with just the difference of the layout called i.e. just replace the fragment XML file name "R.layout.fragment2" for "Fragment2.java" and "R.layout.fragment3" for "Fragment3.java".

4. Now open the MainActivity file

MainActivity.java

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

//The MainActivity extends FragmentActivity instead of normal Activity class.
public class MainActivity extends FragmentActivity {

    Fragment2 fragment2;
    Fragment3 fragment3;

    Boolean isFragment2Showing;

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


        //Initialize fragment2 and fragment3
        fragment2 = new Fragment2();
        fragment3 = new Fragment3();

        // Add the fragment to the FrameLayout
        getSupportFragmentManager().beginTransaction()
                .add(R.id.frameForDynamicFragments, fragment2).commit();

        //This means that fragment2 is visible
        isFragment2Showing = true;

        //Set OnClickListener on button for switching the fragments
        ((Button)findViewById(R.id.switchFragmentsButton)).setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                switchFragments();
            }
        });
    }

    /*
     * Method to replace fragments with slide animation
     */
    private void switchFragments() {

        //Get the supported FragmentManager.
        //It is used for interaction with the Fragment. Remember that Fragments are only supported after API 11 and we have to add the android-support-v4.jar in project dependencies for backword compatability.
        FragmentManager   manager         =   getSupportFragmentManager();
        FragmentTransaction ft            =   manager.beginTransaction();

        //Set the Fragment change animation
        ft.setCustomAnimations(android.R.anim.slide_in_left , android.R.anim.slide_out_right);

        //If fragment2 is showing then change to fragment3
        if (isFragment2Showing) {
              ft.replace(R.id.frameForDynamicFragments, fragment3);
        }
        //else back to fragment 2
        else {
              ft.replace(R.id.frameForDynamicFragments, fragment2);
        }
        ft.commit();
        isFragment2Showing = !isFragment2Showing;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

Please see the comments above the code lines for further explanation.

This should be the final result:

 

 

 

Official Google documentation on Fragments: http://developer.android.com/reference/android/app/Fragment.html