I have an application that I just would like to use in portrait mode, so I have defined
android:screenOrientation="portrait" in the manifest XML. This works OK for the HTC Magic phone (and prevents orientation changes on other phones as well).
But I have a problem with the HTC G1 phone as I open the hardware QWERTY keyboard (not the virtual keyboard). My activity stays in portrait mode, but it seems to get restarted and loses all its states. This does not happen with the HTC Hero version.
My application is quite big, so I don't want it to restart and lose all its states when the keyboard is opened. How can I prevent that?
Update April 2013: Don't do this. It wasn't a good idea in 2009 when I first answered the question and it really isn't a good idea now. See this answer by hackbod for reasons: http://stackoverflow.com/a/5336057/84021
android:configChanges="keyboardHidden|orientation" to your AndroidManifest.xml. This tells the system what configuration changes you are going to handle yourself - in this case by doing nothing.
<activity android:name="MainActivity" android:screenOrientation="portrait" android:configChanges="keyboardHidden|orientation">
See http://developer.android.com/reference/android/R.attr.html#configChanges for more details.
However, your application can be interrupted at any time, e.g. by a phone call, so you really should add code to save the state of your application when it is paused.
Update: As of Android 3.2, you also need to add "screenSize":
<activity android:name="MainActivity" android:screenOrientation="portrait" android:configChanges="keyboardHidden|orientation|screenSize">
Caution: Beginning with Android 3.2 (API level 13), the "screen size" also changes when the device switches between portrait and landscape orientation. Thus, if you want to prevent runtime restarts due to orientation change when developing for API level 13 or higher (as declared by the minSdkVersion and targetSdkVersion attributes), you must include the "screenSize" value in addition to the "orientation" value. That is, you must declare
android:configChanges="orientation|screenSize". However, if your application targets API level 12 or lower, then your activity always handles this configuration change itself (this configuration change does not restart your activity, even when running on an Android 3.2 or higher device).