Force "portrait" orientation mode

Don't apply the orientation to the application element, instead you should apply the attribute to the activity element, and you must also set configChanges as noted below.

Example:

<activity
   android:screenOrientation="portrait"
   android:configChanges="orientation|keyboardHidden">
</activity>

This is applied in the manifest file AndroidManifest.xml.

Note that

android:screenOrientation="portrait"     
android:configChanges="orientation|keyboardHidden"

is added in the manifest file - where the activity is defined.