Android TV-Creating TV Navigation

 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.

 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.

 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:

• Ensure that a user with a D-pad controller can navigate to all visible controls on the screen.
• 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.
• Ensure that switching between controls between controls is straightforward and predictable.

》Note: You should only use these attributes to modify the navigation order if the default order that the system applies does not work well.

<TextView android:id="@+id/Category1"
        android:nextFocusDown="@+id/Category2"\>

Attribute	Function
nextFocusDown	Defines the next view to receive focus when the user navigates down.
nextFocusLeft	Defines the next view to receive focus when the user navigates left.
nextFocusRight	Defines the next view to receive focus when the user navigates right.
nextFocusUp	Defines the next view to receive focus when the user navigates up.

 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.

 Android provides Drawable State List Resources 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:

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