In order for the Android system to restore the state of the views in your activity, each view must have a unique ID

Normally, in the process of carrying out a screen reorientation, the Android platform tears down the foreground activity and recreates it, restoring each of the view values in the activity’s layout.

In an app you’re working on, you notice that a view’s value is not being restored after screen reorientation. What could be a likely cause of the problem that you should verify, at a minimum, about that particular view?

You should verify that it has a valid id. In order for the Android system to restore the state of the views in your activity, each view must have a unique ID, supplied by the android:id attribute.