Android Fragments

In Android a fragment is a "behaviour or a portion of user interface in an Activity". I first met fragments when putting maps in my Android activity. They're also useful for putting various UI components on one activity.
I've adapted this example from here http://developer.android.com/training/basics/fragments/index.html
Here's the simple breakdown of using a list fragment:

1) Create an activity_main.xml in res/layout/ as such:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment android:name="com.example.droidtestnew.smallpage"
              android:id="@+id/article_fragment"
              android:layout_weight="2"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

</LinearLayout>

2) Create another activity_main.xml in res/layout-large/ (note the second fragment):

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment android:name="com.example.droidtestnew.smallpage"
              android:id="@+id/headlines_fragment"
              android:layout_weight="1"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

    <fragment android:name="com.example.droidtestnew.smallpage"
              android:id="@+id/article_fragment"
              android:layout_weight="2"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

</LinearLayout>

3) Create a java class called smallpage.java

package com.example.droidtestnew;

import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.widget.ArrayAdapter;

public class smallpage extends ListFragment {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        String arrHello[] = {
            "Hello One",
            "Goodbye Two"
        };
        
        // We need to use a different list item layout for devices older than Honeycomb
        int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
                android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;

        // Create an array adapter for the list view, using the Ipsum headlines array
        setListAdapter(new ArrayAdapter<String>(getActivity(), layout, arrHello));
    }

}

4) Change MainActivity.java to extend FragmentActivity:

public class MainActivity extends FragmentActivity {

You're done. That should be all you need. If you launch this on a small screen, you'll see the one fragment list, if you launch it on a tablet, you'll see two lists.

Easy as pie! Obviously this is an incredibly basic example, but it should get you started with fragments.