Android Application Components

Android application components work together to create a seamless user experience. If you’re an Android developer, it’s important to understand the different types of components that make up an Android app.

In this article, we will explore the different types of Android application components and their roles in app development.

The components of an Android application are the building blocks of the application. These components are self-contained units that perform specific tasks and can be combined with other components to create a complete application.

In Android, there are Five types of application components:

1. Activities.
2. Services.
3. Broadcast Receivers.
4. Content Providers.
5. Intents

Lets explore each of them in detail.

Activities

Activities are user interface components that represent a single screen in an app. They handle user interactions, such as button clicks, menu selections, and touch events. An app can have multiple activities, and each activity has its own lifecycle. Activities can be used to navigate between different screens within an app and can also be used to start other activities or launch other apps.

As a developer, you should know that an activity is responsible for creating a window on the device’s screen where user interface elements such as buttons, text fields, and images are displayed. When the user interacts with these elements, such as clicking a button or making a gesture, the activity receives and handles the input and may initiate an action or process accordingly.

Activities are not isolated and can communicate with other activities within the same app, as well as with activities in other apps. For instance, an email application may have separate activities for composing, sending, and receiving emails, which can share data and interact with each other.

Moreover, activities have a lifecycle that the Android system manages to optimize memory usage and enhance performance. The lifecycle determines how activities are created, started, paused, resumed, stopped, and destroyed. Understanding this lifecycle is essential for building efficient and robust Android applications.

The syntax for creating an Activity in Android is as follows:

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

// Your code goes here
}
}

The onCreate() method is called when the activity is created, and it is where you should initialize any resources needed by the activity, such as views or data. In this example, we set the content view to activity_main, which is a layout file that defines the user interface for the activity.

This is the basic structure of an activity in Android. To lean more in depth please read our article on android activities.

Services

Services, on the other hand, are components that perform background tasks in an app without an interface. They run in the background even when the app is not active and can perform long-running operations such as downloading files, playing music, or uploading data. Services can run indefinitely, and they do not have a user interface. They are used to perform tasks that need to be executed in the background, without interrupting the user experience.

As a developer, you might find services helpful for carrying out long-running operations such as playing music, handling network transactions, or downloading data from the internet. They can also provide functionality to other applications or system services. A messaging app, for example, might utilize a service to handle incoming messages and notify the user even if the messaging app is not active.

There are two types of services in Android: started and bound services. Started services are initiated by calling the startService() method, and they keep running until the stopService() method is explicitly called. In contrast, bound services are initiated by calling the bindService() method, and they run only as long as the application is bound to the service.

Services usually work in conjunction with other Android components, such as Activities and Broadcast Receivers, to offer a complete user experience. A music player application, for instance, may use a Service to play music in the background, an Activity to display the user interface, and a Broadcast Receiver to handle media button events.

Below code snippet demonstrates the syntax for specifying a service:

public class MyService extends Service {

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// Code to be executed when the service is started
return START_STICKY;
}

@Override
public void onDestroy() {
// Code to be executed when the service is destroyed
}

@Nullable
@Override
public IBinder onBind(Intent intent) {
// Return null if this service does not provide a binding interface
return null;
}
}

Above example defines a class called MyService that extends the Service class. It overrides three methods:

onStartCommand(): This method is called when the service is started. It takes three parameters: an Intent object that contains the command to be executed, a set of flags that indicate how the service should be started, and a unique integer ID that represents the start request. The method should return an integer that indicates what the service should do if it is killed by the system. In this example, START_STICKY is returned, which means the service should be restarted if it is killed. The actual code that performs the desired functionality should be added to the onStartCommand() method.

onDestroy(): This method is called when the service is destroyed. It can be used to perform any cleanup tasks that are necessary.

onBind(): This method is called when another component wants to bind to the service. It returns an IBinder object that can be used to communicate with the service. In this example, null is returned because the service does not provide a binding interface.

Broadcast Receivers

Broadcast Receivers are components that receive and respond to system-wide broadcast announcements. They can be used to start a Service or launch an Activity in response to these events. For example, a broadcast receiver can be used to receive a message when the battery level of a device is low and start a service to conserve battery life.

Another example, an activity can send a broadcast message to a service to indicate that a certain action has been taken by the user. The service can then respond to the message and perform a corresponding action, such as updating a database or sending a notification.

Broadcast Receivers can also be used to trigger the launch of an activity or service in response to a system-wide event. For example, an application can register a Broadcast Receiver to listen for the system boot event. When the device boots up, the Broadcast Receiver will receive the system boot message and can launch a service to perform a certain task, such as downloading updated content for the application.

The syntax for broadcast receiver is shown below:

public class MyReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
// Do something when the broadcast is received
}
}

This is a basic skeleton of a Broadcast Receiver in Android. To use it, you would need to register it in your AndroidManifest.xml file, specifying which event or system broadcast it should listen for.

<receiver android:name=".MyReceiver">
<intent-filter>
<action android:name="android.intent.action.BATTERY_CHANGED" />
</intent-filter>
</receiver>

This tells Android that whenever the battery level changes, it should send a broadcast message with the “android.intent.action.BATTERY_CHANGED” action, which will be received by your MyReceiver class.

Content Providers

A Content Provider acts as a mediator between the application and the underlying data storage. A Content Provider offers a standard interface to read and write data from a data source like a file, database, or web server.

Content providers are particularly useful when multiple applications need to access the same data. Instead of each application accessing the data source directly, they can use the Content Provider to access the data in a consistent and controlled manner. This provides a layer of abstraction that isolates the data from the application code, making it easier to manage and maintain the data.

For example, Android’s contacts application uses a Content Provider to access contact information stored in the device’s database. This allows other applications to access the same contact information without implementing their own database access code.

Another example is the MediaStore Content Provider, which provides access to media files stored on the device, such as images and videos.

To use a Content Provider, an application must first request permission to access the data. This is done using the Android Manifest file. Once permission is granted, the application can use the Content Resolver to interact with the Content Provider.

The Content Resolver provides methods to insert, update, delete, and query data using the Content Provider’s URI (Uniform Resource Identifier).

Here’s the syntax for defining a content provider:

public class MyContentProvider extends ContentProvider {
// Code for content provider goes here
}

The code snippet defines a class named MyContentProvider which extends the ContentProvider class provided by the Android framework.

The ContentProvider class is a fundamental component of the Android platform that provides a standard interface for sharing data between applications.

By extending this class, the MyContentProvider class is able to implement the methods required for a content provider, such as onCreate(), query(), insert(), update(), delete(), and getType().

These methods are responsible for handling data access requests from other applications, performing database operations, and returning results in a format that can be consumed by the requesting application.

Intents

Lastly, Intents are messaging components that allow different components of an app or different apps to communicate with each other.

Intents are used to start activities, launch services, or send broadcast messages.

They can also transfer data between components or apps. Intents can be explicit or implicit, and they can carry data as extras.

In addition to the main application components, Android has several other components essential to the development process.

Overall, understanding the roles of these different Android application components is crucial for developers who want to create high-quality, scalable applications. By leveraging these components effectively, developers can create apps that provide a seamless user experience and perform tasks efficiently.