An Activity is an application component that provides a screen with which users can interact in order to do something, such as dial the phone, take a photo, send an email, or view a map. Each activity is given a window in which to draw its user interface. The window typically fills the screen, but may be smaller than the screen and float on top of other windows. An application usually consists of multiple activities that are loosely bound to each other. Typically, one activity in an application is specified as the "main" activity, which is presented to the user when launching the application for the first time. Each activity can then start another activity in order to perform different actions. Each time a new activity starts, the previous activity is stopped, but the system preserves the activity in a stack . When a new activity starts, it is pushed onto the back stack and takes user focus.

2. Activity
An Activity is an application component that provides a
screen with which users can interact in order to do
something, such as dial the phone, take a photo, send
an email, or view a map.
Each activity is given a window in which to draw
its user interface.
An application usually consists of multiple
activities that are loosely bound to each other.

3. Activity
Each time a new activity starts, the
previous activity is stopped, but the
system preserves the activity in a stack .
When a new activity starts, it is pushed
onto the back stack and takes user
focus.

4. Go Phish! 4
Android
Activity - >

5. Activity life
cycle - >

6. Method Description Next
onCreate() Called when the activity is first created. onStart()
onRestart() Called after your activity has been stopped, just prior to
it being started again.
Always followed by onStart()
onStart()
onStart() Called when the activity is becoming visible to the user.
Followed by onResume() if the activity comes to the
foreground, or onStop() if it becomes hidden.
onResume()or
onStop()
onResume() Called when the activity will start interacting with the
user.
Always followed by onPause().
onPause()
onPause() Called when the system is about to start resuming a
previous activity.
onResume()
or
onStop()
onStop() Called when the activity is no longer visible to the user.
Followed by either onRestart() if this activity is coming
back to interact with the user, or onDestroy() if this
activity is going away.
onRestart()
or
onDestroy()
onDestroy() The final call you receive before your activity is
Go Phish! 6
destroyed.
nothing

7. Example:
When the Activity first time loads the events are called as below:
onCreate()
onStart()
onResume()
When you click on Phone button the Activity goes to the background and the below events
are called:
onPause()
onStop()
Exit the phone dialer and the below events will be called:
onRestart()
onStart()
onResume()
When you click the back button OR try to finish() the activity the events are called as below:
onPause()
onStop()
onDestroy()

8. Activity Stack
• Activities in the system are managed as an activity stack. An activity has essentially four states:
If an activity in the foreground of
the screen (at the top of the stack),
it is active or running.
If an activity is completely obscured
by another activity, it is stopped.
If an activity has lost focus, it
is paused.
If an activity is paused or stopped,
the system can drop the activity
from memory by either asking it to
finish, or simply killing its process.