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Understanding Android Services
In Android, a service is a component that can perform work in the background without providing a user interface. Services are useful when you need to keep doing something even if the user is not actively looking at your app, such as playing music, tracking location, or syncing data with a server.
This chapter introduces the basic ideas behind services, how they differ from other Android components, and the main types of services you will work with. Details about foreground and background behavior, and how to schedule work properly, will be covered in later chapters about Foreground vs Background Services and WorkManager.
What a Service Is and Is Not
A service runs in the same process as your app by default and executes code while your app might not be visible on the screen. Unlike activities, services do not draw anything on the screen and do not directly interact with the user. Unlike broadcast receivers, which respond quickly to events and finish, a service is designed to run longer operations.
You can think of an activity as the visible face of your app and a service as the worker that stays in the background, even if the user switches to another app. However, a service is not a separate process and it is not a separate thread. If you start a long, blocking operation directly in a service, you can still freeze your app unless you manage threads or use other concurrency tools.
A service is not a thread. Starting a service does not automatically create a new thread. Long running or blocking work inside a service must be done on a background thread, such as with Kotlin coroutines or other threading tools.
Main Use Cases for Services
Services are designed for tasks that need to keep running beyond the lifetime of a single activity. Typical situations where services make sense include ongoing background work, tasks that must survive activity changes, and work that must continue even if the user leaves the app.
A common example is playing audio. The user might start a song in your app and then press the Home button, or open another app, but the audio should keep playing. A service can manage the playback and keep running while the user is elsewhere.
Another example is downloading large files or uploading data. If you start a big download inside an activity and the user rotates the device or leaves the screen, that activity might be destroyed. A service can own the download logic and continue it independently of the activity lifecycle.
Location tracking is another typical case. If your app needs to periodically get the device location for navigation or fitness tracking, it can place that logic in a service so that updates still happen when activities come and go.
Later you will see that modern Android puts strong limits on what work can run in the background, especially when the app is not visible. For this reason, services are often combined with foreground notifications or with scheduling components such as WorkManager. At this stage, it is important to understand that services are meant for ongoing or longer operations that outlive a single screen.
Basic Service Lifecycle Ideas
Just like activities have a lifecycle, services also have a lifecycle with specific callback methods. You do not need to memorize the details here, but you should know that a service is created, can start running, and eventually is destroyed.
The core idea is that the system calls lifecycle methods on your service at certain times. For example, a base service class will typically override methods that are called when the service is first created and when it is finally removed from memory. There is also a method called when work is requested, which depends on the type of service.
The service lifecycle is more limited than the activity lifecycle. Services do not have visible states like started, paused, or resumed in the way that activities do. Instead, the focus is on when they start work, how long they run, and what happens if the system kills them because of memory pressure.
Android can stop a background service when the device is low on resources or when the system needs to improve battery life. If that happens, your service may receive no direct warning. For important ongoing tasks, you will learn to use foreground services, which are given higher priority and must show a notification to the user.
Started and Bound Services
At a high level, Android has two main ways to work with a service: started and bound. It is possible for a single service to support both. The distinction is about how the service is used and how long it should stay alive.
A started service begins when some component, usually an activity, explicitly requests that it start doing work. The component does not need a direct two way connection after that. Once started, the service can keep running until it decides to stop itself or until the system stops it. This style is suitable for doing one time or ongoing tasks in the background, such as a single large download or continuous playback.
A bound service, on the other hand, exposes an interface that other components can connect to. Clients bind to the service and can call its methods, often within the same process. When the last client unbinds, the service can be destroyed. This is more like a local server inside your app that provides features such as playing or pausing media, or retrieving the current status of some background operation.
In practice, started services are easier to understand. You tell them to start, they do their job, and they stop. Bound services are more interactive and often require slightly more complex setup, but they allow you to share a long running feature across multiple activities or fragments in your app.
The Role of Foreground Services
Android requires user awareness for some types of continuous background work, especially when it can affect battery life or user privacy. For these situations, you place your service in the foreground, which is a special kind of started service that shows a non dismissible notification.
Foreground services are appropriate for tasks that the user has requested and expects to continue, such as turn by turn navigation, tracking a workout, voice calls, or ongoing music playback. The notification informs the user that your app is performing work even though it may not be currently visible.
Foreground services are less likely to be killed by the system than ordinary background services. However, they must follow stricter rules, including showing a visible notification and sometimes requesting special permissions. There are also category restrictions for when you can use them. The details of all these rules will be covered in the Foreground vs Background Services chapter.
Background Execution Limits
Modern Android versions strongly limit background execution to preserve battery and performance. A simple always running background service is no longer acceptable in most situations. Instead, Android encourages you to use services together with scheduling and constraints, depending on the type of work.
For example, if your app needs to sync data with a server every few hours, it is not allowed to keep a service running all the time just for that purpose. Instead, you use background scheduling tools such as WorkManager, which will choose the right time to run your tasks according to system policies, connectivity, and battery conditions.
For work that must run immediately and continue, such as current user actions, foreground services are usually required. For delayed or periodic work, background scheduling is preferred. The exact rules and techniques will be discussed when you study WorkManager and lifecycle aware tasks.
Do not rely on long running background services that stay alive indefinitely. Modern Android versions limit background services heavily. For most persistent or periodic tasks, use scheduled work with components like WorkManager.
Service and App Process Relationship
A service is part of your app package and, by default, shares the same process as your activities. This means that all components of your app can share the same memory and resources. If the system kills your process, all your activities, services, and other components inside it are gone.
You can technically configure a service to run in a different process using settings in the manifest file, but this is an advanced scenario and has a cost. Separate processes increase memory usage and complicate communication. For most beginner applications you will keep services in the default process and focus on how to correctly manage their lifecycle and workload.
It is important to understand that even though a service allows your app to continue doing work when no activity is visible, the app itself is still running from the system point of view. That means any background work affects device battery, memory, and performance. Android monitors these effects and may limit your service if it causes too much load.
Declaring a Service in the Manifest
Before the system can start a service, it must know about it. This is done by declaring the service in your AndroidManifest.xml. The manifest informs the system about all components of your app, including activities, services, broadcast receivers, and content providers.
For a service, the manifest entry specifies its class name and certain attributes that control how it behaves. An example declaration looks like this.
<service
android:name=".MyExampleService"
android:exported="false" />
The android:name attribute points to the service class in your code. The android:exported attribute controls whether components from other apps can interact with your service. For beginners, it is usually set to false for safety, so only your own app components can start or bind to this service.
If your service needs special permissions, or if it acts as a foreground service in specific categories, you add more attributes and sometimes metadata. These advanced details will be introduced later, especially when working with permissions and foreground services.
Starting Work in a Service
Once a service is declared, your app can ask the system to start it or bind to it. You do not create new instances of services directly with constructors. Instead, you use an Intent that identifies the service and hand it to the Android system.
From an activity or other component, you can request the service to start by calling a specific method and passing an intent that targets the service class. When you do this, the system creates the service if needed and then calls its lifecycle callbacks to begin work.
For bound services, components use a different method to establish a connection that allows two way communication. When the last connection is removed, the system can stop the service automatically.
Because intents and inter component communication are covered in other chapters, you do not need to know the exact code here. At this point it is enough to understand that services are not instantiated directly. The system manages their creation and destruction when you request them through well defined methods.
When to Use Services in Your Apps
As you start developing real applications, it is important to recognize when a service is needed and when it is not. If your task is short and only needed while an activity is visible, you often do not need a service at all. Running a coroutine or a background thread inside the activity can be enough, as long as you handle lifecycle properly.
You reach for a service when your work must survive the activity lifecycle or must continue while the user does something else. For example, a podcast player that keeps audio playing when the screen is off, a file transfer that should end even if the user leaves the app, or a navigation app that keeps providing directions while it runs in the background.
At the same time, you should avoid creating services for everything. Each service adds complexity and potential battery cost. For delayed or periodic background work that does not need to start immediately, you will later learn to use WorkManager instead of a manually controlled service.
A good guiding question is: does this work need to keep going when my activities are gone or when the user is not in my app? If the answer is yes, then a service, usually combined with foreground behavior or scheduling, is a good candidate. If the answer is no, then simpler lifecycle aware tools inside your UI components may be better.
Summary
Services are Android components that allow your app to keep performing tasks in the background without showing a user interface. They are not threads and do not automatically run work off the main thread, so you still need background execution tools to avoid blocking the user interface.
You have two main interaction patterns: started services that perform ongoing or one shot tasks and bound services that let other components interact with them through a defined interface. Foreground services are a special form that keep the user informed with a visible notification and are used for important ongoing work.
Modern Android imposes strict limits on background execution, so services must be used carefully and are often combined with scheduling components such as WorkManager. In the next chapters you will explore how foreground and background services differ in practice and how WorkManager helps you run reliable background work in a battery friendly way.