Answers for "set app always portrait"

only portrait mode android studio

<activity android:name=".YourActivity"
    android:configChanges="orientation"
    android:screenOrientation="portrait"/>

how to fix portrait orientation for android apps

<activity
            android:name="com.example.demo_spinner.MainActivity"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
</activity>

<!-- Do this in AndroidMainifest.xml-->

<!--Additionaly, you can also use screenOrientation="sensorPortrait" 
if you want to enable rotation by 180 degrees.-->

<!--android:screenOrientation="nosensor"
This will lead to forcing your app to portrait on most phones
and landscape on tablets. -->