page.title=Tab Layout
parent.title=Hello, Views
parent.link=index.html
@jd:body
<p>To create a tabbed UI, you need to use a {@link android.widget.TabHost} and a {@link
android.widget.TabWidget}. The {@link android.widget.TabHost} must be the root node for the layout,
which contains both the {@link android.widget.TabWidget} for displaying the tabs and a {@link
android.widget.FrameLayout} for displaying the tab content.</p>
<p>You can implement your tab content in one of two ways: use the tabs to swap
{@link android.view.View}s within the same {@link android.app.Activity}, or use the tabs to change
between entirely separate activities. Which method you want for your application will depend on your
demands, but if each tab provides a distinct user activity, then it probably makes sense to use
a separate {@link android.app.Activity} for each tab, so that you can better manage the application
in discrete groups, rather than one massive application and layout.</p>
<p>In this tutorial, you'll create a tabbed UI that uses a separate {@link
android.app.Activity} for each tab.</p>
<ol>
<li>Start a new project named <em>HelloTabWidget</em>.</li>
<li>First, create three separate {@link android.app.Activity} classes in your project:
<code>ArtistsActivity</code>, <code>AlbumsActivity</code>, and <code>SongsActivity</code>. These
will each represent a separate tab. For now, make each one display a simple message using a {@link
android.widget.TextView}. For example:
<pre>
public class ArtistsActivity extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView textview = new TextView(this);
textview.setText("This is the Artists tab");
setContentView(textview);
}
}
</pre>
<p>Notice that this doesn't use a layout file. Just create a {@link
android.widget.TextView}, give it some text and set that as the content. Duplicate this for
each of the three activities, and add the corresponding <code><activity/></code> tags to the Android Manifest file.</p>
<li>You need an icon for each of your tabs. For each icon, you should create two versions: one
for when the tab is selected and one for when it is unselected. The
general design recommendation is for the selected icon to be a dark color (grey), and the
unselected icon to be a light color (white). (See the <a
href="{@docRoot}guide/practices/ui_guidelines/icon_design.html#tabstructure">Icon Design
Guidelines</a>.) For example:
<p>
<img src="images/ic_tab_artists_white.png" title="unselected tab icon" alt="" />
<img src="images/ic_tab_artists_grey.png" title="selected tab icon" alt="" />
</p>
<p>For this tutorial, you can copy these images and use them for all three tabs. (When you
create tabs in your own application, you should create customized tab icons.)</p>
<p>Now create a <a
href="{@docRoot}guide/topics/resources/drawable-resource.html#StateList">state-list drawable</a>
that specifies which image to use for each tab state:</p>
<ol>
<li>Save the icon images in your project <code>res/drawable/</code> directory.</li>
<li>Create a new XML file in <code>res/drawable/</code>
named <code>ic_tab_artists.xml</code> and insert the following:
<pre>
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<!-- When selected, use grey -->
<item android:drawable="@drawable/ic_tab_artists_grey"
android:state_selected="true" />
<!-- When not selected, use white-->
<item android:drawable="@drawable/ic_tab_artists_white" />
</selector>
</pre>
<p>This is a <a
href="{@docRoot}guide/topics/resources/drawable-resource.html#StateList">state-list drawable</a>,
which you will apply as the tab image. When the tab state changes, the tab icon will
automatically switch between the images defined here.</p>
</li>
</ol>
</li>
<li>Open the <code>res/layout/main.xml</code> file and insert the following:
<pre>
<?xml version="1.0" encoding="utf-8"?>
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="5dp">
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="5dp" />
</LinearLayout>
</TabHost>
</pre>
<p>This is the layout that will display the tabs and provide navigation between each {@link
android.app.Activity} created above.</p>
<p>The {@link android.widget.TabHost} requires that a {@link android.widget.TabWidget} and a
{@link android.widget.FrameLayout} both live somewhere within it. To position the {@link
android.widget.TabWidget} and {@link android.widget.FrameLayout} vertically, a {@link
android.widget.LinearLayout} is used. The {@link android.widget.FrameLayout} is where the content
for each tab goes, which is empty now because the {@link android.widget.TabHost} will automatically
embed each {@link android.app.Activity} within it.</p>
<p>Notice that the {@link android.widget.TabWidget} and the {@link android.widget.FrameLayout}
elements have the IDs {@code tabs} and {@code tabcontent}, respectively. These names
must be used so that the {@link android.widget.TabHost} can retrieve references to each of
them. It expects exactly these names.</p>
</li>
<li>Now open <code>HelloTabWidget.java</code> and make it extend {@link
android.app.TabActivity}:</p>
<pre>
public class HelloTabWidget extends TabActivity {
</pre>
</li>
<li>Use the following code for the {@link android.app.Activity#onCreate(Bundle) onCreate()}
method:
<pre>
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Resources res = getResources(); // Resource object to get Drawables
TabHost tabHost = getTabHost(); // The activity TabHost
TabHost.TabSpec spec; // Resusable TabSpec for each tab
Intent intent; // Reusable Intent for each tab
// Create an Intent to launch an Activity for the tab (to be reused)
intent = new Intent().setClass(this, ArtistsActivity.class);
// Initialize a TabSpec for each tab and add it to the TabHost
spec = tabHost.newTabSpec("artists").setIndicator("Artists",
res.getDrawable(R.drawable.ic_tab_artists))
.setContent(intent);
tabHost.addTab(spec);
// Do the same for the other tabs
intent = new Intent().setClass(this, AlbumsActivity.class);
spec = tabHost.newTabSpec("albums").setIndicator("Albums",
res.getDrawable(R.drawable.ic_tab_albums))
.setContent(intent);
tabHost.addTab(spec);
intent = new Intent().setClass(this, SongsActivity.class);
spec = tabHost.newTabSpec("songs").setIndicator("Songs",
res.getDrawable(R.drawable.ic_tab_songs))
.setContent(intent);
tabHost.addTab(spec);
tabHost.setCurrentTab(2);
}
</pre>
<p>This sets up each tab with their text and icon, and assigns each one an {@link
android.app.Activity}.</p>
<p>A reference to the {@link android.widget.TabHost} is first captured with {@link
android.app.TabActivity#getTabHost()}. Then, for
each tab, a {@link android.widget.TabHost.TabSpec} is created to define the tab properties. The
{@link android.widget.TabHost#newTabSpec(String)} method creates a new {@link
android.widget.TabHost.TabSpec} identified by the given string tag. For each
{@link android.widget.TabHost.TabSpec}, {@link
android.widget.TabHost.TabSpec#setIndicator(CharSequence,Drawable)} is called to set the text and
icon for the tab, and {@link android.widget.TabHost.TabSpec#setContent(Intent)} is called to specify
the {@link android.content.Intent} to open the appropriate {@link android.app.Activity}. Each
{@link android.widget.TabHost.TabSpec} is then added to the {@link android.widget.TabHost} by
calling {@link android.widget.TabHost#addTab(TabHost.TabSpec)}.</p>
<p>At the very end, {@link
android.widget.TabHost#setCurrentTab(int)} opens the tab to be displayed by default, specified
by the index position of the tab.</p>
<p>Notice that not once was the {@link android.widget.TabWidget} object referenced. This is
because a {@link android.widget.TabWidget} must always be a child of a {@link
android.widget.TabHost}, which is what you use for almost all interaction with the tabs. So when
a tab is added to the {@link android.widget.TabHost}, it's automatically added to the child
{@link android.widget.TabWidget}.</p>
</li>
<li>Now open the Android Manifest file and add the <code>NoTitleBar</code> theme to the
<em>HelloTabWidget</em>'s
<code><activity></code> tag. This will remove the default application title from the top
of the layout, leaving more space for the tabs, which effectively operate as their own titles.
The <code><activity></code> tag should look like this:
<pre>
<activity android:name=".HelloTabWidget" android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar">
</pre>
</li>
<li>Run the application.</li>
</ol>
<p>Your application should look like this (though your icons may be different):</p>
<img src="images/hello-tabwidget.png" width="150px" />
<h3>References</h3>
<ul>
<li>{@link android.widget.TabWidget}</li>
<li>{@link android.widget.TabHost}</li>
<li>{@link android.widget.TabHost.TabSpec}</li>
<li>{@link android.widget.FrameLayout}</li>
</ul>