android-7.0.0_r1/s

page.title=Building Layouts for TV
page.tags=tv
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="#themes">Use Layout Themes for TV</a></li>
    <li><a href="#structure">Build Basic TV Layouts</a></li>
    <li><a href="#visibility">Build Useable Text and Controls</a></li>
    <li><a href="#density-resources">Manage Layout Resources for TV</a></li>
    <li><a href="#anti-patterns">Avoid Layout Anti-Patterns</a></li>
    <li><a href="#large-bitmaps">Handle Large Bitmaps</a></li>
    <li><a href="#advertising">Provide Effective Advertising</a></li>
  </ol>
  <h2>You should also read</h2>
  <ol>
    <li><a href="{@docRoot}design/tv/index.html">Android TV Design</a></li>
  </ol>
</div>
</div>

<p>
  A TV screen is typically viewed from about 10 feet away, and while it is much larger than most
  other Android device displays, this type of screen does not provide the same level of precise
  detail and color as a smaller device. These factors require you to create app layouts with TV
  devices in mind in order to create a useful and enjoyable user experience.
</p>

<p>
  This lesson describes the minimum requirements and implementation details for building effective
  layouts in TV apps.
</p>

<h2 id="themes">Use Layout Themes for TV</h2>

<p>
  Android <a href="{@docRoot}guide/topics/ui/themes.html">Themes</a> can provide a basis for
  layouts in your TV apps. You should use a theme to modify the display of your app activities that
  are meant to run on a TV device. This section explains which themes you should use.
</p>

<h3 id="leanback-theme">Leanback theme</h3>

<p>
  A support library for TV user interfaces called the <a href=
  "{@docRoot}tools/support-library/features.html#v17-leanback">v17 leanback library</a> provides a
  standard theme for TV activities, called {@code Theme.Leanback}. This theme establishes a
  consistent visual style for TV apps. Use of this theme is recommended for most TV apps. This
  theme is strongly recommended for any TV app that uses v17 leanback classes. The following code
  sample shows how to apply this theme to a given activity within an app:
</p>

<pre>
&lt;activity
  android:name="com.example.android.TvActivity"
  android:label="&#64;string/app_name"
  <strong>android:theme="&#64;style/Theme.Leanback"</strong>&gt;
</pre>


<h3 id="notitle-theme">NoTitleBar theme</h3>

<p>
  The title bar is a standard user interface element for Android apps on phones and tablets, but it
  is not appropriate for TV apps. If you are not using v17 leanback classes, you should apply this
  theme to your TV activities to suppress the display of a title bar. The following code example
  from a TV app manifest demonstrates how to apply this theme to remove the display of a title bar:
</p>

<pre>
&lt;application&gt;
  ...

  &lt;activity
    android:name="com.example.android.TvActivity"
    android:label="&#64;string/app_name"
    <strong>android:theme="&#64;android:style/Theme.NoTitleBar"</strong>&gt;
    ...

  &lt;/activity&gt;
&lt;/application&gt;
</pre>


<h2 id="structure">Build Basic TV Layouts</h2>

<p>Layouts for TV devices should follow some basic guidelines to ensure they are usable and
  effective on large screens. Follow these tips to build landscape layouts optimized for TV screens:
</p>

<ul>
  <li>Build layouts with a landscape orientation. TV screens always display in landscape mode.</li>
  <li>Put on-screen navigation controls on the left or right side of the screen and save the
    vertical space for content.</li>
  <li>Create UIs that are divided into sections, using <a href="{@docRoot}guide/components/fragments.html"
    >Fragments</a>, and use view groups like {@link android.widget.GridView} instead of {@link
    android.widget.ListView} to make better use of the horizontal screen space.
  </li>
  <li>Use view groups such as {@link android.widget.RelativeLayout} or {@link
    android.widget.LinearLayout} to arrange views. This approach allows the system to adjust the
    position of the views to the size, alignment, aspect ratio, and pixel density of a TV screen.</li>
  <li>Add sufficient margins between layout controls to avoid a cluttered UI.</li>
</ul>


<h3 id="overscan">Overscan</h3>

<p>Layouts for TV have some unique requirements due to the evolution of TV standards and the
  desire to always present a full screen picture to viewers. For this reason, TV devices may
  clip the outside edge of an app layout in order to ensure that the entire display is filled.
  This behavior is generally referred to as <em>overscan</em>.
</p>

<p>Screen elements that must be visible to the user at all times should be positioned within the
overscan safe area. Adding a 5% margin of 48dp on the left and right edges and 27dp on the top and
bottom edges to a layout ensures that screen elements in that layout will be within the overscan
safe area.
</p>

<p>Background screen elements that the user doesn't directly interact with should not be adjusted or
clipped to the overscan safe area. This approach ensures that background screen elements look
correct on all screens.
</p>

<p>The following example shows a root layout that can contain background elements, and a nested
child layout that has a 5% margin and can contain elements within the overscan safe area:
</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   &gt;

   &lt;!-- Screen elements that can render outside the overscan safe area go here --&gt;

   &lt;!-- Nested RelativeLayout with overscan-safe margin --&gt;
   &lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:layout_marginTop="27dp"
       android:layout_marginBottom="27dp"
       android:layout_marginLeft="48dp"
       android:layout_marginRight="48dp"&gt;

      &lt;!-- Screen elements that need to be within the overscan safe area go here --&gt;

   &lt;/RelativeLayout&gt;
&lt;/RelativeLayout&gt;
</pre>

<p class="caution">
  <strong>Caution:</strong> Do not apply overscan margins to your layout if you are using the
  v17 leanback classes, such as {@link android.support.v17.leanback.app.BrowseFragment} or related
  widgets, as those layouts already incorporate overscan-safe margins.
</p>

<h2 id="visibility">Build Useable Text and Controls</h2>

<p>
  The text and controls in a TV app layout should be easily visible and navigable from a distance.
  Follow these tips to make your user interface elements easier to see from a distance:
</p>

<ul>
  <li>Break text into small chunks that users can quickly scan.</li>
  <li>Use light text on a dark background. This style is easier to read on a TV.</li>
  <li>Avoid lightweight fonts or fonts that have both very narrow and very broad strokes.
  Use simple sans-serif fonts and anti-aliasing to increase readability.</li>
  <li>Use Android's standard font sizes:
<pre>
&lt;TextView
      android:id="@+id/atext"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:gravity="center_vertical"
      android:singleLine="true"
      <strong>android:textAppearance="?android:attr/textAppearanceMedium"/&gt;</strong>
</pre>
  </li>
  <li>Ensure that all your view widgets are large enough to be clearly visible to someone
    sitting 10 feet away from the screen (this distance is greater for very large screens). The
    best way to do this is to use layout-relative sizing rather than absolute sizing, and
    density-independent pixel (dip) units instead of absolute pixel units. For example, to set the
    width of a widget, use {@code wrap_content} instead of a pixel measurement, and to set the
    margin for a widget, use dip values instead of px values.</li>
</ul>

<p>
  For more information about density-independent pixels and building layouts to handle larger
  screen sizes, see <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple
  Screens</a>.
</p>

<h2 id="density-resources">Manage Layout Resources for TV</h2>

<p>The common high-definition TV display resolutions are 720p, 1080i, and 1080p.
  Your TV layout should target a screen size of 1920 x 1080 pixels, and then allow the Android
  system to downscale your layout elements to 720p if necessary. In general, downscaling
  (removing pixels) does not degrade your layout presentation quality. However, upscaling can
  cause display artifacts that degrade the quality of your layout and have a negative impact on
  the user experience of your app.</p>

<p>
  To get the best scaling results for images, provide them as
  <a href="{@docRoot}tools/help/draw9patch.html">9-patch image</a> elements if possible. If you
  provide low quality or small images in your layouts, they will appear pixelated, fuzzy, or
  grainy, which is not a good experience for the user. Use high-quality images instead.
</p>

<p>
  For more information on optimizing layouts and resources for large screens see
  <a href="{@docRoot}training/multiscreen/index.html">Designing for multiple screens</a>.
</p>


<h2 id="anti-patterns">Avoid Layout Anti-Patterns</h2>

<p>
  There are a few approaches to building layouts that you should avoid because they do not work
  well on TV devices and lead to bad user experiences. Here are some user interface approaches you
  should specifically <em>not</em> use when developing a layout for TV.
</p>

<ul>
  <li><strong>Re-using phone or tablet layouts</strong> - Do not reuse layouts from a phone or
    tablet app without modification. Layouts built for other Android device form factors are not
    well suited for TV devices and should be simplified for operation on a TV.</li>
  <li><strong>ActionBar</strong> - While this user interface convention is recommended for use
    on phones and tablets, it is not appropriate for a TV interface. In particular, using an
    action bar options menu (or any pull-down menu for that matter) is strongly discouraged, due
    to the difficulty in navigating such a menu with a remote control.</li>
  <li><strong>ViewPager</strong> - Sliding between screens can work great on a phone or tablet,
    but don't try this on a TV!</li>
</ul>

<p>For more information on designing layouts that are appropriate to TV, see the
  <a href="{@docRoot}design/tv/index.html">TV Design</a> guide.</p>


<h2 id="large-bitmaps">Handle Large Bitmaps</h2>

<p>TV devices, like any other Android device, have a limited amount of memory. If you build your
  app layout with very high-resolution images or use many high-resolution images in the operation
  of your app, it can quickly run into memory limits and cause out of memory errors.
  To avoid these types of problems, follow these tips:</p>

<ul>
  <li>Load images only when they are displayed on the screen. For example, when displaying multiple
  images in a {@link android.widget.GridView} or {@link android.widget.Gallery}, only load an image
  when {@link android.widget.Adapter#getView getView()} is called on the
  view's {@link android.widget.Adapter}.
  </li>
  <li>Call {@link android.graphics.Bitmap#recycle()} on {@link android.graphics.Bitmap} views that
  are no longer needed.
  </li>
  <li>Use {@link java.lang.ref.WeakReference} for storing references to {@link
  android.graphics.Bitmap} objects in an in-memory {@link java.util.Collection}.
  </li>
  <li>If you fetch images from the network, use {@link android.os.AsyncTask} to fetch and store
  them on the device for faster access. Never do network transactions on the application's main
  user interface thread.
  </li>
  <li>Scale down large images to a more appropriate size as you download them; otherwise,
  downloading the image itself may cause an out of memory exception.
  </li>
</ul>

<p>
  For more information on getting the best performance when working with images, see
  <a href="{@docRoot}training/displaying-bitmaps/index.html">Displaying Bitmaps Efficiently</a>.
</p>

<h2 id="advertising">Provide Effective Advertising</h2>

<p>For the living room environment, we recommend you use video ads solutions
that are full-screen and dismissable within 30 seconds. Functionality for
advertising on Android TV, such as dismiss buttons and clickthroughs, must be
accessible using the D-pad rather than touch.</p>

<p>Android TV does not provide a web browser. Your ads must not attempt to
launch a web browser or redirect to Google Play Store content that is not
approved for Android TV devices.</p>

<p class="note">
  <strong>Note:</strong> You can use the {@link android.webkit.WebView} class
  for logins to services like Google+ and Facebook.
</p>