Lifecycle

Question 1

Explain the android activity lifecycle?

Answer 1

As a user navigates inside & outside of an app, the activities transition through different states.

A number of call-backs are provided to let the app know that there has been a state change.

We can use these call-back methods to manage how the app reacts to the changes in state.

For example, if we have a high data intensive app then we can unsubscribe from any data changes when the app is in the background and re-subscribe when the user resumes the app.

Question 2

What are some examples of using life cycle callback methods?

Answer 2

• A stock monitoring app can unsubscribe from price changes when the app triggers onPause() and re-subscribe on resume.
• A video streaming app can pause the stream onPause(), resume at same point on resume.

Question 3

What are the core six callback methods in the activity lifecycle?

Answer 3

• onCreate()
• onStart()
• onResume()
• onPause()
• onStop()
• onDestroy()

Question 4

In what stage of the lifecycle can the app process be killed?

Answer 4

When the activity goes into the background or is no longer visible (onPause() / onStop()). The app process may then be killed because a higher priority app needs more memory. When the user navigates back to the app, the onCreate() method is executed.

Question 5

In what situation is the onRestart() callback method called?

Answer 5

When the activity has entered the onStop() state and the user navigates back to the activity. The onStart() method is then called afterwards.