Embedded Files
Components of Android Applications
Definition
Android applications are built using a set of fundamental components that work together to create the overall user experience. Each component plays a distinct role, contributing to the app's functionality and behavior. These components are activated through a combination of user interactions and system events. The eight main components of Android applications are as follows:
1.Activities
An Activity represents a single screen with a user interface (UI) where users can interact with the app. It is one of the primary building blocks of an Android app.
Purpose
Each activity performs a specific task, such as displaying a form, a list, or a web page.
Lifecycle
An activity goes through a lifecycle from creation to destruction, including states like onCreate(), onStart(), onResume(), onPause(), onStop(), and onDestroy().
Example
The main screen of an app, where users log in or view content, is typically an activity.
2. Services
A Service is a component that runs in the background to perform long-running operations or tasks without user interaction. Unlike activities, services do not have a user interface.
Purpose
Services are used for tasks that continue even when the app is not in the foreground, such as playing music, downloading files, or syncing data.
Types:
Started Service: Initiated when a component (such as an activity) starts it, and it runs until stopped.
Bound Service: Allows other components to bind to it and interact with it.
Example:
A music player app continues playing music through a service even when the user navigates away from the app.
3. Broadcast Receivers
A Broadcast Receiver is a component that listens for system-wide broadcast announcements or intents and responds accordingly.
Purpose
It allows the app to react to events, such as when the phone battery is low, the screen is turned on, or an incoming message is received.
System Broadcasts: Android sends various system events that apps can listen for, such as the device booting up, network changes, or airplane mode being turned on.
Example
An app can use a broadcast receiver to react when the device connects to Wi-Fi by automatically syncing data.
4. Content Providers
A Content Provider manages access to a structured set of data within an app or shares data with other apps.
Purpose
Content providers allow apps to interact with data stored in databases, files, or the cloud, using a uniform API.
Data Sharing: They facilitate data sharing between apps. For example, one app can access a user's contacts stored by another app.
Example
The Contacts app uses a content provider to store and retrieve contact information. Another app can request access to read the contacts through this content provider.
5. Fragments
A Fragment is a portion of an activity's UI that can be reused across multiple activities.
Purpose
Fragments allow developers to break down the UI into smaller components that can be used and managed independently.
Lifecycle: Fragments have their own lifecycle, which is managed by the host activity.
Example
In a tablet app, a fragment can display a list of items on one side of the screen, while another fragment shows the details of the selected item on the other side.
6. Intents
An Intent is a messaging object that facilitates communication between components, such as starting activities, services, or broadcasting system events.
Explicit Intents: Used to start specific activities or services within the same app.
Implicit Intents: Used to request actions from other apps, like opening a URL or sharing content.
7. Resources
Android apps use various resources, such as images, strings, and layouts, to define how the UI looks and functions. These resources are stored in the res folder and can be referenced in code or XML layouts.
Types of Resources: Drawable resources (images), layout resources (XML files defining UI), and string resources (text).
Localization: Resources help localize apps for different languages and regions.
8. Manifest File
Every Android app contains a Manifest.xml file that provides essential information about the app to the Android system.
Component Declaration: The manifest file declares all components, such as activities, services, broadcast receivers, and content providers.
Permissions: The file specifies the permissions the app needs, such as access to the internet or the device’s camera.
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