Check out example codes for "how to fix portrait orientation for android apps". It will help you in understanding the concepts better.

Code Example 1

<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. -->

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