Android Activity Life Cycle
Importance of Activity's Life cycle
Understanding Android Activity Life cycle is one of the most important things for android developers. Using the activity life cycle correctly can avoid your application from:
- Losing the user data when the screen orientation changes
- Crashing of application while switching between applications
- Consuming valuable resources of the phone while the user is not using you app
- Losing the users data when user leaves you app and return later
Here an important point is, the activity is recreated with the phone's orientation is changes. So to give your users best experience, you need to take care of this too.
Activity Life cycle Callbacks
To give the users of your application best user experience, it is very important to understand the activity life cycle. To manage you activities, android provides various callbacks on different stages of activity life cycle. They are listed below:
- onCreate()
- onStart()
- onResume()
- onPause()
- onStop()
- onRestart()
- onDestroy()
They all are called on different stages of activity life. To understand which callback is called when, see the table and image from the official documentation of android below carefully. And also see the demo project running given at the end of the tutorial.
 |
| Android Activity Life Cycle |
| Method | Description |
|---|---|
| onCreate | called when activity is first created. You must implement this callback. |
| onStart | When the activity enters the Started state, the system invokes this callback. The system prepares to enter the activity to foreground. |
| onResume | called when activity will be in visible form to the user. This is the state in which the app interacts with the user. |
| onPause | called when activity is not in focus. It is the first indication that the user is leaving the activity. It does not mean that activity is going to destroy. When a new dialog(popup) or multi window in android 7.0 and higher is made, it is also called as the app loses the focus. |
| onStop | called when activity is no longer visible to the user. It usually happens when a new activity is launched. |
| onRestart | called after your activity is stopped, prior to start. |
| onDestroy | called before the activity is destroyed. After that your activity will be removed from the memory. |
Save the State of your App
To save the state of your application, android provides two callbacks onSaveInstanceState(Bundle savedInstanceState) and onRestoreInstanceState(Bundle savedInstanceState). From these two callbacks, you can save and restore the data and make the user experience better. These callbacks are called when the orientation of the app is changed or app is brought to foreground again. onSaveInstanceState(Bundle savedInstanceState) is called after onPause() and similarly onRestoreInstanceState(Bundle savedInstanceState) is called onStart() method.
Demo Project
To understand the activity life cycle more clearly, run the demo project at Github Repository. Here you will see all the callbacks in action and also learn how you can save the user data and make the better user experience. If you want to know anything about it or having some confusing, feel free to comment or contact me at farooqahmadkhan003@gmail.com
