What Is the Android Activity Lifecycle?

Activity is crucial in Android application development, and understanding the life cycle of Activity is the key to mastering Activity. This article will explore the life cycle of Android Activity in depth.

Activity is a single screen in an Android application, similar to a window in a desktop application or a Frame in a Java program, used to organize UI components and controls onto the screen. An activity has a life cycle, and its status changes according to application and user interaction.

Lifecycle method

The life cycle of an Android Activity includes a series of method callbacks. When the Activity state changes, the corresponding method will be called:

onCreate() : Called at creation time, used to initialize components and set layouts. onStart() : Activity is called when it is about to be visible to the user. onResume() : Called when the activity is restored to the foreground and begins to interact with the user. onPause() : Called when the activity is about to lose focus, and is usually used for time-consuming operations such as saving data and stopping animations. onStop() : Activity is called when it is invisible to the user and is used to release resources. onDestroy() : Called before Activity, used to free all resources. onSaveInstanceState() : Called when the Activity is about to be destroyed, and is used to save the status information of the Activity. onRestoreInstanceState() : Called when the Activity is restored from the destroyed state, used to restore the status information of the Activity.

onSaveInstanceState() method uses a Bundle object to save instance state, but is limited to tracking information about various EditText controls. When the Activity instance is destroyed and recreated, the system uses the saved data to restore the Activity state. You are still responsible for saving and restoring any additional information you wish to retain between different Activity instances.

To extract the saved state from the Bundle and restore it, implement onRestoreInstanceState() method. For example, if the app's main Activity has a submit button that takes the user to MainActivity and then clicks the Submit button, a callback to MainActivity is triggered. Clicking the "Submit" button should take us to onCreate() , onResume() is triggered for MainActivity, and now MainActivity is no longer visible. Therefore, the MainActivity is triggered next.

A new activity or dialog appears on the screen

Various events may place new activities in the foreground, such as users answering calls or using shortcut gestures. In this case, the callback sequence of the Activity will depend on whether the new Activity completely or partially overwrites your Activity.

When partially overridden, your Activity will trigger a callback to onResume() when it returns to the foreground.

When fully overridden, your Activity will quickly trigger callbacks to onStop() and onPause() in turn. If your Activity returns to the foreground, a callback to onStart() and onResume() will be triggered.

in conclusion

After reading this article, you should have a good understanding of how the Activity life cycle works. You also learn about two ways to start an Activity, as well as some tips on how to handle instance state during the Activity lifecycle.

Thank you for reading. If you are interested in Android application development, please check out our other articles on Android application development.

This article has been updated and includes contributions from Nitish Kumar. Nitish is a web developer with experience in creating e-commerce websites on a variety of platforms. He uses his free time to work on personal projects to make his daily life easier or to take long night walks with friends.

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