Add android:screenOrientation="portrait"
to the activity in the AndroidManifest.xml. For example:
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<activity
android:name="com.neundorfer.microraphandheld.v1.ParentActivity"
android:label="@string/app_name"
android:screenOrientation="portrait">