Activity lifecycle - onCreate called on every re-orientation

Activity is recreated after each rotation by default. You can override this behaviour with configChanges attribute of the activity tag in AndroidManifest. For further details and different options, see http://developer.android.com/guide/topics/resources/runtime-changes.html

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 decalare 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).

http://developer.android.com/guide/topics/resources/runtime-changes.html

What happen when orientation changed

Life Cycle of orientation

onPause();
onSaveInstanceState();
onStop();
onDestroy();

onCreate();
onStart();
onResume();

---- app recreated and now is running ---

If you do long operation in onCreate() and want prevent re-create your activity add configChanges attribute in your mainfest

<activity android:name=".MyActivity"
          android:configChanges="orientation|keyboardHidden|screenSize"
          android:label="@string/app_name">

screenSize if you targeting api >= 13