android_frameworks_base/docs/html/training/tv/start/navigation.jd

page.title=Creating TV Navigation
page.tags=tv, d-pad, focus
helpoutsWidget=true
trainingnavtop=true

@jd:body

<div id="tb-wrapper">
<div id="tb">
  <h2>This lesson teaches you how to</h2>
  <ol>
    <li><a href="#d-pad-navigation">Enable D-pad Navigation</a></li>
    <li><a href="#focus-selection">Provide Clear Focus and Selection</a></li>
  </ol>

</div>
</div>

<p>
  TV devices provide a limited set of navigation controls for apps. Creating an effective
  navigation scheme for your TV app depends on understanding these limited controls and the limits
  of users' perception while operating your app. As you build your Android app for TVs,
  pay special attention to how the user actually navigates around your app when using remote
  control buttons instead of a touch screen.
</p>

<p>
  This lesson explains the minimum requirements for creating effective TV app navigation scheme and
  how to apply those requirements to your app.
</p>


<h2 id="d-pad-navigation">Enable D-pad Navigation</h2>

<p>
  On a TV device, users navigate with controls on a remote control device, using either a
  directional pad (D-pad) or arrow keys. This type of control limits movement to up, down, left,
  and right. To build a great TV-optimized app, you must provide a navigation scheme where the user
  can quickly learn how to navigate your app using these limited controls.
</p>

<p>
  The Android framework handles directional navigation between layout elements automatically, so
  you typically do not need to do anything extra for your app. However, you should thoroughly test
  navigation with a D-pad controller to discover any navigation problems. Follow these guidelines to
  test that your app's navigation system works well with a D-pad on a TV device:
</p>

<ul>
  <li>Ensure that a user with a D-pad controller can navigate to all visible controls on the
  screen.
  </li>
  <li>For scrolling lists with focus, make sure that the D-pad up and down keys scroll the list,
    and the Enter key selects an item in the list. Verify that users can select an element in the
    list and that the list still scrolls when an element is selected.
  </li>
  <li>Ensure that switching between controls between controls is straightforward and predictable.
  </li>
</ul>


<h3 id="modify-d-pad-nav">Modifying directional navigation</h3>

<p>
  The Android framework automatically applies a directional navigation scheme based on the
  relative position of focusable elements in your layouts. You should test the generated
  navigation scheme in your app using a D-pad controller. After testing, if you decide you want
  users to move through your layouts in a specific way, you can set up explicit directional
  navigation for your controls.
</p>

<p class="note">
  <strong>Note:</strong> You should only use these attributes to modify the navigation order if the
  default order that the system applies does not work well.
</p>

<p>
  The following code sample shows how to define the next control to receive focus for a {@link
  android.widget.TextView} layout object:
</p>

<pre>
&lt;TextView android:id="&#64;+id/Category1"
        android:nextFocusDown="&#64;+id/Category2"\&gt;
</pre>

<p>
  The following table lists all of the available navigation attributes for Android user interface
  widgets:
</p>

<table>
  <tr>
    <th>Attribute</th>
    <th>Function</th>
  </tr>
  <tr>
    <td>{@link android.R.attr#nextFocusDown}</td>
    <td>Defines the next view to receive focus when the user navigates down.</td>
  </tr>
  <tr>
    <td>{@link android.R.attr#nextFocusLeft}</td>
    <td>Defines the next view to receive focus when the user navigates left.</td>
  </tr>
  <tr>
    <td>{@link android.R.attr#nextFocusRight}</td>
    <td>Defines the next view to receive focus when the user navigates right.</td>
  </tr>
  <tr>
    <td>{@link android.R.attr#nextFocusUp}</td>
    <td>Defines the next view to receive focus when the user navigates up.</td>
  </tr>
</table>

<p>
  To use one of these explicit navigation attributes, set the value to the ID ({@code android:id}
  value) of another widget in the layout. You should set up the navigation order as a loop, so that
  the last control directs focus back to the first one.
</p>



<h2 id="focus-selection">Provide Clear Focus and Selection</h2>

<p>
  The success of an app's navigation scheme on TV devices is depends on how easy it is for
  a user to determine what user interface element is in focus on screen. If you do not provide
  clear indications of focused items (and therefore what item a user can take action on), they can
  quickly become frustrated and exit your app. For the same reason, it is important to always have
  an item in focus that a user can take action on immediately after your app starts, or any time
  it is idle.
</p>

<p>
  Your app layout and implementation should use color, size, animation, or a combination of these
  attributes to help users easily determine what actions they can take next. Use a uniform scheme
  for indicating focus across your application.
</p>

<p>
  Android provides <a href="{@docRoot}guide/topics/resources/drawable-resource.html#StateList">
  Drawable State List Resources</a> to implement highlights for focused and selected controls. The
  following code example demonstrates how to enable visual behavior for a button to indicate that a
  user has navigated to the control and then selected it:
</p>

<pre>
&lt;!-- res/drawable/button.xml --&gt;
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
    &lt;item android:state_pressed="true"
          android:drawable="@drawable/button_pressed" /&gt; &lt;!-- pressed --&gt;
    &lt;item android:state_focused="true"
          android:drawable="@drawable/button_focused" /&gt; &lt;!-- focused --&gt;
    &lt;item android:state_hovered="true"
          android:drawable="@drawable/button_focused" /&gt; &lt;!-- hovered --&gt;
    &lt;item android:drawable="@drawable/button_normal" /&gt; &lt;!-- default --&gt;
&lt;/selector&gt;
</pre>

<p>
  The following layout XML sample code applies the previous state list drawable to a
  {@link android.widget.Button}:
</p>

<pre>
&lt;Button
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:background="@drawable/button" /&gt;
</pre>

<p>
  Make sure to provide sufficient padding within the focusable and selectable controls so that the
  highlights around them are clearly visible.
</p>

<p>
  For more recommendations on designing effective selection and focus for your TV app, see
  <a href="{@docRoot}design/tv/patterns.html">Patterns for TV</a>.
</p>