Explain Activity LifeCycle.

                                                    

1)onCreate()
                  Called when activity is first created.

2)onStart()
                   Called when Activity is visible to User.

3)onResume()
                     Called when activity will start interacting with user.

4)onPause()
                    Called when activity went to background but not be killed.

5)onStop()
                   Called when activity UI is not visisble to user.

6)onRestart()
                    Called activity  started again.

7)onDestroy()
                  Called before activity is destroyed.