Handling Focus

The framework will handle routine focus movement in response to user input. This includes changing the focus as Views are removed or hidden, or as new Views become available. Views indicate their willingness to take focus through the isFocusable() method. To change whether a View can take focus, call setFocusable() . When in touch mode, you may query whether a View allows focus with isFocusableInTouchMode() . You can change this with setFocusableInTouchMode() .

Focus movement is based on an algorithm which finds the nearest neighbor in a given direction. In rare cases, the default algorithm may not match the intended behavior of the developer. In these situations, you can provide explicit overrides with the following XML attributes in the layout file: nextFocusDown, nextFocusLeft, nextFocusRight, and nextFocusUp. Add one of these attributes to the View from which the focus is leaving. Define the value of the attribute to be the id of the View to which focus should be given. For example:

<LinearLayout android:orientation="vertical" ... >

<Button android:id="@+id/top"

android:nextFocusUp="@+id/bottom" ... />

<Button android:id="@+id/bottom"

android:nextFocusDown="@+id/top" ... />

</LinearLayout>

For a touch-capable device, once the user touches the screen, the device will enter touch mode. From this point onward, only Views for which isFocusableInTouchMode() is true will be focusable, such as text editing widgets. Other Views that are touchable, like buttons, will not take focus when touched; they will simply fire their on-click listeners when pressed.

Any time a user hits a directional key or scrolls with a trackball, the device will exit touch mode, and find a view to take focus. Now, the user may resume interacting with the user interface without touching the screen.

Ordinarily, in this vertical layout, navigating up from the first Button would not go anywhere, nor would navigating down from the second Button. Now that the top Button has defined the bottom one as the nextFocusUp (and vice versa), the navigation focus will cycle from top-to-bottom and bottom-to-top.

If you'd like to declare a View as focusable in your UI (when it is traditionally not), add the android:focusable XML attribute to the View, in your layout declaration. Set the value true. You can also declare a View as focusable while in Touch Mode with android:focusableInTouchMode.

To request a particular View to take focus, call requestFocus() .

To listen for focus events (be notified when a View receives or looses focus), use onFocusChange() , as discussed in the Event Listeners section, above.

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