Android TV - 1.3 Building Layouts for TV

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Building Layouts for TV

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Android TV Design

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.

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

Use Layout Themes for TV

Android Themes 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.

Leanback theme

A support library for TV user interfaces called the v17 leanback library provides a standard theme for TV activities, called 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:

<activity
  android:name="com.example.android.TvActivity"
  android:label="@string/app_name"
  android:theme="@style/Theme.Leanback">

NoTitleBar theme

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:

<application>
  ...

  <activity
    android:name="com.example.android.TvActivity"
    android:label="@string/app_name"
    android:theme="@android:style/Theme.NoTitleBar">
    ...

  </activity>
</application>

Build Basic TV Layouts

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:

Build layouts with a landscape orientation. TV screens always display in landscape mode.
Put on-screen navigation controls on the left or right side of the screen and save the vertical space for content.
Create UIs that are divided into sections, using Fragments, and use view groups like GridView instead ofListView to make better use of the horizontal screen space.
Use view groups such as RelativeLayout or 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.
Add sufficient margins between layout controls to avoid a cluttered UI.

Overscan

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 overscan.

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.

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.

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:

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

   <!-- Screen elements that can render outside the overscan safe area go here -->

   <!-- Nested RelativeLayout with overscan-safe margin -->
   <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">

      <!-- Screen elements that need to be within the overscan safe area go here -->

   </RelativeLayout>
</RelativeLayout>

Caution: Do not apply overscan margins to your layout if you are using the v17 leanback classes, such asBrowseFragment or related widgets, as those layouts already incorporate overscan-safe margins.

Build Useable Text and Controls

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:

Break text into small chunks that users can quickly scan.
Use light text on a dark background. This style is easier to read on a TV.
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.

Use Android's standard font sizes:

<TextView
      android:id="@+id/atext"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:gravity="center_vertical"
      android:singleLine="true"
      android:textAppearance="?android:attr/textAppearanceMedium"/>

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 wrap_content instead of a pixel measurement, and to set the margin for a widget, use dip values instead of px values.

For more information about density-independent pixels and building layouts to handle larger screen sizes, seeSupporting Multiple Screens.

Manage Layout Resources for TV

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.

To get the best scaling results for images, provide them as 9-patch image 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.

For more information on optimizing layouts and resources for large screens see Designing for multiple screens.

Avoid Layout Anti-Patterns

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 notuse when developing a layout for TV.

Re-using phone or tablet layouts - 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.
ActionBar - 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.
ViewPager - Sliding between screens can work great on a phone or tablet, but don't try this on a TV!

For more information on designing layouts that are appropriate to TV, see the TV Design guide.

Handle Large Bitmaps

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:

Load images only when they are displayed on the screen. For example, when displaying multiple images in aGridView or Gallery, only load an image when getView() is called on the view's Adapter.
Call recycle() on Bitmap views that are no longer needed.
Use WeakReference for storing references to Bitmap objects in an in-memory Collection.
If you fetch images from the network, use AsyncTask to fetch and store them on the device for faster access. Never do network transactions on the application's main user interface thread.
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.

For more information on getting the best performance when working with images, see Displaying Bitmaps Efficiently.

Provide Effective Advertising

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.

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.

Note: You can use the WebView class for logins to services like Google+ and Facebook.

Next: Creating TV Navigation