In what state or states of an activity can a user interact with it?

In the case of Android, an activity represents a single screen with a user interface just like windows form in vb.net or frame of Java. Activity is a java class in Android which has some pre-defined functions which are triggered at different App states, which developer can override to perform anything they want to do.

They are four states of activity

1. 1. Active
2. 2. Paused
3. 3. Stopped
4. 4. Destroyed

In the case of active state only users interact with the activity.