Beginning Android

is available to your activity via getPackageManager().

The queryIntentActivityOptions() method takes some of the same parameters as does addIntentOptions(), notably the caller ComponentName, the “specifics” array of Intent instances, the overall Intent representing the actions you are seeking, and the set of flags. It returns a List of Intent instances matching the stated criteria, with the “specifics” ones first.

If you would like to offer alternative actions to users, but by means other than addIntentOptions() , you could call queryIntentActivityOptions(), get the Intent instances, then use them to populate some other user interface (e.g., a toolbar).

CHAPTER 26 Handling Rotation

Some Android handsets, like the T-Mobile G1, offer a slide-out keyboard that triggers rotating the screen from portrait to landscape. Other handsets might use accelerometers to determine screen rotation, like the iPhone does. As a result, it is reasonable to assume that switching from portrait to landscape and back again may be something your users will look to do.

Android has a number of ways for you to handle screen rotation, so your application can properly handle either orientation. All these facilities do is help you detect and manage the rotation process — you are still required to make sure you have layouts that look decent on each orientation.

A Philosophy of Destruction

By default, when there is a change in the phone configuration that might affect resource selection, Android will destroy and re-create any running or paused activities the next time they are to be viewed. While this could happen for a variety of different configuration changes (e.g., change of language selection), it will most likely trip you up mostly for rotations, since a change in orientation can cause you to load a different set of resources (e.g., layouts).

The key here is that this is the default behavior. It may even be the behavior that is best for one or more of your activities. You do have some control over the matter, though, and can tailor how your activities respond to orientation changes or similar configuration switches.

It’s All The Same, Just Different

Since, by default, Android destroys and re-creates your activity on a rotation, you may only need to hook into the same onSaveInstanceState() that you would if your activity were destroyed for any other reason (e.g., low memory). Implement that method in your activity and fill in the supplied Bundle with enough information to get you back to your current state. Then, in onCreate() (or onRestoreInstanceState(), if you prefer), pick the data out of the Bundle and use it to bring your activity back to the way it was.

To demonstrate this, let’s take a look at the Rotation/RotationOne project. It, and the other sample projects used in this chapter, which are also found in the source code section of the Apress web site, use a pair of main.xml layouts, one in res/layout/ and one in res/layout-land/ for use in landscape mode. Here is the portrait layout:

<?xml version='1.0' encoding='utf-8'?>
<LinearLayout xmlns:android='http://schemas.android.com/apk/res/android'
 android:orientation='vertical'
 android:layout_width='fill_parent'
 android:layout_height='fill_parent'
>
 <Button android:id='@+id/pick'
  android:layout_width='fill_parent'
  android:layout_height='fill_parent'
  android:layout_weight='1'
  android:text='Pick'
  android:enabled='true'
 />
 <Button android:id='@+id/view'
  android:layout_width='fill_parent'
  android:layout_height='fill_parent'
  android:layout_weight='1'
  android:text='View'
  android:enabled='false'
 />
</LinearLayout>

while here is the similar landscape layout:

<?xml version='1.0' encoding='utf-8'?>
<LinearLayout xmlns:android='http://schemas.android.com/apk/res/android'
 android:orientation='horizontal'
 android:layout_width='fill_parent'
 android:layout_height='fill_parent'
>
 <Button android:id='@+id/pick'
  android:layout_width='fill_parent'
  android:layout_height='fill_parent'
  android:layout_weight='1'
  android:text='Pick'
  android:enabled='true'
 />
 <Button android:id='@+id/view'
  android:layout_width='fill_parent'
  android:layout_height='fill_parent'
  android:layout_weight='1'
  android:text='View'
  android:enabled='false'
/>
</LinearLayout>

Basically, it is a pair of buttons, each taking up half the screen. In portrait mode, the buttons are stacked; in landscape mode, they are side-by-side.

If you were to simply create a project, put in those two layouts, and compile it, the application would appear to work just fine — a rotation (Ctrl-F12 in the emulator) will cause the layout to change. And while buttons