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Understanding the Android App Lifecycle
Android apps are not like simple programs that start, run, and then exit when the user closes them. On Android, the system is constantly creating, destroying, pausing, and resuming parts of your app to balance performance, memory, and user experience. The concept that describes how an app behaves from the moment it is opened until it is completely removed from memory is called the app lifecycle.
This chapter gives you the big picture of how Android manages your app over time and why this matters when you build real applications. Later chapters in this section will focus on activities specifically, lifecycle callbacks, and configuration changes in more detail. Here the focus stays on the overall lifecycle behavior that is common to Android apps as a whole.
Processes, Components, and the System
An Android app usually lives inside a process managed by the operating system. Within that process, different components of your app can exist at different times. The two components that are most relevant to the lifecycle are activities and services, but in this chapter we will think mostly in terms of the overall app as the user experiences it.
The system can create your app process when it needs to run something from your app, and it can remove that process when it needs memory for other apps. This can happen even if the user did not press a close button. Instead of you deciding when your app ends, Android decides based on what the user is doing and how much memory is available.
Your responsibility as a developer is to respect this control. You must save important data at the right time, free resources when you do not need them, and avoid assuming that your app will keep running in the background forever.
Android can destroy your app’s process at any time when system resources are low, even if the user has not explicitly closed your app.
Visible, Background, and Killed States
From the user’s point of view, an app is either on screen, in the background, or gone. Internally, these states map to different priorities that the system keeps for your app process.
When your app is in the foreground, the user can see it and interact with it. This is the time when Android gives your process the highest priority. Your code should focus on fast user interaction, smooth animations, and responsive input. Heavy work during this time may cause visible delays, which leads to a poor experience.
When your app is in the background, the user has moved to another app or the home screen. The system wants to keep your app alive so the user can return quickly, but it may kill your process if memory is needed elsewhere. Background apps must be prepared to be removed at any time and then recreated when the user returns.
If your app is killed, the process is gone from memory. The user can still reach your app from the recent apps list or launcher, but Android will recreate it almost as if it is starting from scratch. Any critical state that you did not save will be lost.
A key idea here is that background does not always mean running. Your app can be considered in the background from the user’s perspective, but the process itself might be completely terminated if the system needs to reclaim memory.
User Navigation and Lifecycle Transitions
The lifecycle of your app is mostly driven by user actions. When the user taps your app icon, Android starts a new process, launches the first screen, and brings it to the foreground. As the user navigates between screens, jumps to another app, or presses the Back or Home buttons, Android moves your app through different lifecycle states.
Pressing the Home button typically sends your app to the background. The current screen is no longer visible, but Android keeps your state in memory when possible. Pressing the Back button usually signals that the user is finished with that particular screen. If the user backs out of the last screen in your app, the app is removed from the recent navigation stack, so returning to it will recreate it from the beginning.
When the user switches between multiple apps quickly, Android tries to preserve the state of the apps involved. However, when resources are limited on the device, your app may be one of the first candidates to be removed if it is not in active use.
Understanding this behavior helps you design predictable navigation flows. You should not try to override the user’s expectations by keeping activities alive in unusual ways or by blocking normal navigation. Instead, design your app so it behaves naturally with the system navigation rules.
State Persistence and Restoration
Because Android may destroy your app while it is not actively in use, you must plan for the possibility that the user will return to your app after it has been removed from memory. Your code should save enough information to restore the user experience so that it feels continuous.
There are two main types of state you will need to think about. Short term state describes what is currently visible on screen. This may include text typed into a form, the scroll position of a list, or which tab is selected. This state should be saved and restored so that when the user rotates the screen or leaves and returns quickly, everything looks as they left it.
Long term state represents data that is important even across full app restarts or device reboots, such as saved notes, preferences, or login status. This data is usually stored in shared preferences, a database, or files. From the app lifecycle perspective, you should commit long term state to persistent storage when it changes, not only at lifecycle boundaries, because you can not rely on receiving a final callback before the system destroys your process.
Short term state is more tightly connected to lifecycle events and is typically saved at specific moments, then restored when the app recreates its screens. Later chapters in this section will show you the exact lifecycle callbacks where this saving and restoring should happen.
Never assume that your app will receive a final chance to save data before being killed. Persist important data as soon as it is confirmed, not only in shutdown related callbacks.
Resource Management and Performance
Another important aspect of the Android app lifecycle is when to acquire and release resources. A resource can be anything that has a cost, such as memory, battery, network usage, sensors, location updates, or open files. Keeping these resources active when your app is not visible can drain the device and create a poor experience.
In practice, you should acquire resources only when needed and release them when your app moves out of the active part of its lifecycle. For example, a camera preview that the user sees on screen should stop when the app is not visible. Continuous location tracking should also pause or switch to a lower power mode when the app is in the background.
You must also be careful with background work. Long running tasks that continue after the user leaves your app should only run when they are truly necessary, and they should use the correct tools provided by the system, such as services or WorkManager, instead of trying to hold your whole app process alive manually. Misusing background work easily leads to performance issues, high battery use, and increased chance that the system kills your app.
Proper resource management is not only a performance concern. It is also a requirement to pass app store quality checks and to avoid user complaints. As you learn more about lifecycle callbacks, you will see that Android gives you specific moments when you should start and stop expensive work.
Lifecycle and Configuration Changes
While this chapter focuses on the overall lifecycle, a special case worth mentioning is configuration changes. A configuration change is any change to device properties that affects how your app should present itself. Common examples are rotations between portrait and landscape modes and language changes.
On many configuration changes, Android tears down and recreates parts of your app so that it can adapt to the new configuration. This is not a crash or an error; it is a normal part of the lifecycle. Your app must treat these restarts as expected and must restore user visible state smoothly.
From an app lifecycle point of view, configuration changes are another reason why you cannot treat your app as a single continuous run. Instead, think of your app as something that may be recreated many times during its lifetime, often while the user is still actively using it. Proper lifecycle handling ensures that these recreations are invisible to the user and that your app feels stable and well designed.
Thinking the “Android Way”
The biggest mental shift for beginners is to stop thinking about the app lifecycle as something they control directly and to start thinking in terms of cooperating with the system. You launch work in response to lifecycle events, you save and restore state when told to, and you accept that the system can remove your process at any time.
This cooperation brings benefits. Android can keep your app feeling smooth, manage memory efficiently, and provide a consistent user experience across all apps. When you use the lifecycle correctly, your app will start faster, use less battery, and behave predictably when users switch tasks, rotate the device, or come back after some time.
As you proceed through the next chapters, you will learn about the specific lifecycle of activities, the callbacks that Android gives to you, and how to handle configuration changes. All of those details build on the ideas you encountered here: apps are managed by the system, they move between visible and background states, they may be killed and recreated, and your code must handle these transitions gracefully.