android_frameworks_base/docs/html/training/basics/fragments/creating.jd

page.title=Creating a Fragment
parent.title=Building a Dynamic UI with Fragments
parent.link=index.html

trainingnavtop=true
previous.title=Using the Android Support Library
previous.link=support-lib.html
next.title=Building a Flexible UI
next.link=fragment-ui.html

@jd:body

<div id="tb-wrapper">
  <div id="tb">
    
    <h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#Create">Create a Fragment Class</a></li>
  <li><a href="#AddInLayout">Add a Fragment to an Activity using XML</a></li>
</ol>

    <h2>You should also read</h2>
    <ul>
      <li><a href="{@docRoot}guide/components/fragments.html">Fragments</a></li>
    </ul>

<h2>Try it out</h2>
    
<div class="download-box">
 <a href="http://developer.android.com/shareables/training/FragmentBasics.zip"
class="button">Download the sample</a>
 <p class="filename">FragmentBasics.zip</p>
</div>

  </div>
</div>

<p>You can think of a fragment as a modular section of an activity, which has its own lifecycle,
receives its own input events, and which you can add or remove while the activity is running (sort
of like a "sub activity" that you can reuse in different activities). This lesson shows how to
extend the {@link android.support.v4.app.Fragment} class using the Support Library so your app
remains compatible with devices running system versions as old as Android 1.6.</p>

<p class="note"><strong>Note:</strong> If you decide for other reasons that the minimum
API level your app requires is 11 or higher, you don't need to use the Support
Library and can instead use the framework's built in {@link android.app.Fragment} class and related
APIs. Just be aware that this lesson is focused on using the APIs from the Support Library, which
use a specific package signature and sometimes slightly different API names than the versions
included in the platform.</p>



<h2 id="Create">Create a Fragment Class</h2>

<p>To create a fragment, extend the {@link android.support.v4.app.Fragment} class, then override 
key lifecycle methods to insert your app logic, similar to the way you would with an {@link
android.app.Activity} class.</p>

<p>One difference when creating a {@link android.support.v4.app.Fragment} is that you must use the
{@link android.support.v4.app.Fragment#onCreateView onCreateView()} callback to define the layout.
In fact, this is the only callback you need in order to get a fragment running. For
example, here's a simple fragment that specifies its own layout:</p>

<pre>
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.ViewGroup;

public class ArticleFragment extends Fragment {
    &#64;Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
        Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.article_view, container, false);
    }
}
</pre>

<p>Just like an activity, a fragment should implement other lifecycle callbacks that allow you to
manage its state as it is added or removed from the activity and as the activity transitions
between its lifecycle states. For instance, when the activity's {@link
android.app.Activity#onPause()} method is called, any fragments in the activity also receive a call
to {@link android.support.v4.app.Fragment#onPause()}.</p>

<p>More information about the fragment lifecycle and callback methods is available in the <a
href="{@docRoot}guide/components/fragments.html">Fragments</a> developer guide.</p>



<h2 id="AddInLayout">Add a Fragment to an Activity using XML</h2> 

<p>While fragments are reusable, modular UI components, each instance of a {@link
android.support.v4.app.Fragment} class must be associated with a parent {@link
android.support.v4.app.FragmentActivity}. You can achieve this association by defining each
fragment within your activity layout XML file.</p>

<p class="note"><strong>Note:</strong> {@link android.support.v4.app.FragmentActivity} is a
special activity provided in the Support Library to handle fragments on system versions older than
API level 11. If the lowest system version you support is API level 11 or higher, then you can use a
regular {@link android.app.Activity}.</p>

<p>Here is an example layout file that adds two fragments to an activity when the device
screen is considered "large" (specified by the <code>large</code> qualifier in the directory
name).</p>

<p><code>res/layout-large/news_articles.xml:</code></p>
<pre>
&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    &lt;fragment android:name="com.example.android.fragments.HeadlinesFragment"
              android:id="@+id/headlines_fragment"
              android:layout_weight="1"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

    &lt;fragment android:name="com.example.android.fragments.ArticleFragment"
              android:id="@+id/article_fragment"
              android:layout_weight="2"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

&lt;/LinearLayout>
</pre>

<p class="note"><strong>Tip:</strong> For more information about creating layouts for different
screen sizes, read <a href="{@docRoot}training/multiscreen/screensizes.html">Supporting Different
Screen Sizes</a>.</p>

<p>Here's how an activity applies this layout:</p>

<pre>
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;

public class MainActivity extends FragmentActivity {
    &#64;Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.news_articles);
    }
}
</pre>


<p class="note"><strong>Note:</strong> When you add a fragment to an activity layout by defining
the fragment in the layout XML file, you <em>cannot</em> remove the fragment at runtime. If you plan
to swap your fragments in and out during user interaction, you must add the fragment to the activity
when the activity first starts, as shown in the next lesson.</p>