Android-03 Android Application Basics

Anatomy of an Android Application

• The anatomy of an Android application refers to the structure and organization of files and folders in an Android project
• It helps developers understand how different components are arranged and how an app is built and executed

java (Source Code Folder)

• Contains the main source code of the application
• Includes Java or Kotlin files such as MainActivity.java
• Handles the logic and functionality of the application

res (Resources Folder)

• Contains all non-code resources used in the application
• Includes subfolders like:
  • layout → XML files for UI design (activity_main.xml)
  • drawable → Images and graphics
  • values → Strings, colors, styles
• Helps in designing UI and managing resources efficiently

manifests Folder

• Contains the AndroidManifest.xml file
• It is a mandatory configuration file for every Android app
• Declares application components such as activities, services, and permissions
• Provides essential information to the Android system about the app

Gradle Scripts

• Used for build and dependency management
• Defines project configuration, libraries, and SDK versions
• Helps in compiling and packaging the application

Activity

• Represents a single screen with user interface
• Acts as an entry point for user interaction
• Every Android application must have at least one activity

Resources and UI Components

• Includes layouts, strings, colors, and images
• Defines how the application looks and behaves
• Managed through XML files in the res folder

The Core Components of Android

• Android applications are built using core components that define the structure and behavior of the app
• These components help in handling user interaction, background processing, communication, and data management

Activity

• Activity represents a single screen with a user interface
• It is the main entry point for user interaction in an application
• Each activity is responsible for displaying UI and handling user actions
• Example: Login screen, Home screen
• Managed by Activity Lifecycle methods like onCreate(), onStart(), onResume(), etc.

Service

• Service is a component that runs in the background without a user interface
• Used to perform long-running operations
• Continues running even when the user is not interacting with the app
• Example: Playing music, downloading data in background
• Improves application performance by handling tasks separately from UI

Broadcast Receiver

• Broadcast Receiver is used to respond to system-wide events or messages
• It listens for broadcast intents sent by the system or other applications
• Does not have a user interface
• Example: Battery low notification, incoming SMS alert
• Helps in handling global events efficiently

Content Provider

• Content Provider is used to manage and share application data between different applications
• Provides a standard interface to access structured data
• Data can be stored in databases, files, or other storage systems
• Example: Contacts, media files
• Ensures data security and controlled access using permissions

Intent

• In Android, components communicate with each other using Intents
• Intent is a fundamental concept used to start activities, services, or send messages between components
• It enables interaction within an application as well as between different applications

What is an Intent

• Intent is a messaging object used to request an action from another Android component
• It is used to start an Activity, Service, or Broadcast Receiver
• It acts as a bridge between different components
• It can carry data using key-value pairs (extras)
• It helps in navigation and communication within the app

Explicit Intent

• Explicit Intent is used to start a specific component by clearly specifying its class name
• It is mainly used within the same application
• The developer knows exactly which activity or service should be opened
• Provides direct and controlled communication between components
• Example of Explicit Intent
  • Intent intent = new Intent(this, SecondActivity.class);
  • startActivity(intent);

Implicit Intent

• Implicit Intent is used when the target component is not specified
• The Android system automatically selects the appropriate component based on the action and data
• Used to perform common actions like opening a website, dialing a number, or sharing content
• Allows interaction with other applications
• Example of Implicit Intent
  • Intent intent = new Intent(Intent.ACTION_VIEW);
  • intent.setData(Uri.parse("https://www.google.com"));
  • startActivity(intent);

Android Manifest file

• AndroidManifest.xml is a core configuration file in every Android application
• It provides essential information about the app to the Android system
• Without this file, an Android application cannot run
• AndroidManifest.xml is a mandatory file that defines the structure and components of an Android app
• It tells the system about app components, permissions, and other configurations
• The Android system reads this file before launching the application

Important Elements of Android Manifest File

• <manifest>

  • Root element of the manifest file
  • Contains package name and basic information about the application
  • All other elements are included inside this tag

• <application>

  • Defines application-level information
  • Includes app name, icon, theme, and other properties
  • Contains declarations of activities, services, and other components

• <activity>

  • Declares an activity (screen) in the application
  • Each activity must be defined in the manifest file
  • Can include intent filters to specify how it is launched

• <intent-filter>

  • Specifies the type of intents that the component can respond to
  • Used to define actions like MAIN and categories like LAUNCHER
  • Helps in launching the app from the home screen

• <service>

  • Declares a service component that runs in the background
  • Used for long-running operations without UI

• <receiver>

  • Declares a Broadcast Receiver
  • Used to handle system-wide or app-wide events

• <provider>

  • Declares a Content Provider
  • Used to manage and share data between applications

• <uses-permission>

  • Specifies permissions required by the application
  • Example: Internet access, camera, storage
  • Ensures security and controlled access to device features

Resource Management in Android

• Resource management in Android refers to organizing and managing non-code elements used in an application
• Resources are stored in the res folder and help in designing UI and maintaining consistency
• It improves reusability, maintainability, and localization of the application

String Resources

• Stored in strings.xml file inside res/values folder
• Used to define text values instead of hardcoding in code
• Helps in easy modification and localization (multi-language support)
• Example:
  • MyApp
  • Used in layout: android:text="@string/app_name"

Color Resources

• Stored in colors.xml file inside res/values folder
• Used to define color values for UI elements
• Helps maintain consistent color theme across the app
• Example:
  • <color name="primary">#6200EE</color>
  • Used in layout: android:textColor="@color/primary"

Image Resources

• Stored in res/drawable folder
• Includes images like PNG, JPG, SVG, etc.
• Used for icons, backgrounds, and graphics
• Example:
  • android:src="@drawable/logo"

Layout Resources

• Stored in res/layout folder as XML files
• Defines the structure and design of the user interface
• Contains UI components like TextView, Button, EditText, etc.
• Example:
  • <LinearLayout>
  • <TextView android:text="Hello"/>
  • </LinearLayout>

XML Resources

• XML is used to define various configurations and UI elements
• Includes layout files, animation files, styles, and menus
• Stored in different folders inside res (layout, anim, menu, values, etc.)
• Helps separate design from code and improves readability

---

Questions

1. Define Android Application.
2. What is an Activity in Android?
3. What is a Fragment?
4. Define Intent in Android.
5. What is Android Manifest file?
6. Explain components of Android Application.
7. Explain explicit and implicit intents with example.
8. Explain Services and Broadcast Receivers in Android.
9. Explain the role of Manifest file in Android Application.
10. Explain different types of resources in Android.