Android Components

Before getting started with android programming, we need to know some of the basic components of Android applications. These are the buildings blocks of Android applications. These will let us understand Android application from scratch.

There are Following Components in android:

- Activities

-View/User Interface(UI)

-Intents

-Services

-Content Provider

-BroadCast Receiver

 Activities:
An activity in Android represents a single screen with user interface. An android application typically consists of several activities.  An activity interacts with the user to do one thing, only ONE, such as Unlock screen, dial a phone, view home etc. An application consists of multiple activities that are loosely bound together. But only one activity can be specified as main activity which is displayed while launching the application. Every time an activity starts previous activity is stopped but the data is preserved.

         For instance an email application will have one activity to display list of new emails, another activity to compose email, another activity for reading emails and so on.

The above figure show is the screen with multiple fields like TextView, EditText, Analog Clock and buttons so this is the best example of Activity.

View:

An activity contains views and viewgroups. Views in Andriod are UI components that could be used to build user interface. Examples are buttons, label, and text boxes. One or more views can be grouped together into a ViewGroup. Types of View in android.

• Basic Views
• List Views
• Picker Views
• Menus
• Display Views
• Additional Views

ViewGroup provides a layout where you can order the appearance of views.       Android support the following view groups.·      

• LinearLayout
• TableLayout
• AbsoluteLayout
• FrameLayout
• RelativeLayout
• ScrollView

Services:

Services are something that does not require user interface. It performs operation without user interaction in the background but does not get initiated without user invocation. Another component such as an activity should invoke. To be more technical, service does not have an independent thread, they make use of the main thread from hosting process. For instance you can download something while you get involved in some other application, where download is a service running in background.

Services can be defined in the Manifest.xml as the below mentioned code.

<service android:name=".ServiceClassName" />

All Android services are implemented as a subclass of Service class defined in Android SDK. There are two types of services in Android.

They are:

Unbound Services:

Its a type of service which is not bounded to any components. Once started, it will run in the background even after the component that started the service gets killed. It can be run in the background indefinitely and should stop by itself after the operation its intended to carry out is completed.

Bound Services

Its bound to other components and runs only till the component to which it is bounded runs.

  

Content Providers:

Android is embedded with SQLite Database where all your data gets stored. Content providers in Android manage data that is being shared by more than one application. Consider a case where your Contacts are stored in centralized repository, so here many applications may require access to it or may even require modifying it. In such cases these applications need to query the centralized repository through content providers, so an application with proper permissions can read or modify the Contacts based on permissions. Content provider is concept evolved to manage common data based on permissions. This is a critical concept that has led to develop in-house android applications in a better way.

We will see in details about Content Providers with the Example in coming tutorials.

Broadcast Receivers:

Broadcast receiver is also a component where you can register for system or application events. Once registered you will be notified about the events. Broadcast originates from the system as well as applications. Instance for broadcast originating from the system is ‘low battery notification’. Application level is, like when you download an mp3 file, Mp3 player gets notified about it, and gets added to player list. For this action to take place, mp3 player has to register for this event.

Many system wide events broadcast their information. For example

·         When SMS / Call is received

·         Battery low

·         Network state Changed

·         Photo captured from camera

·         Phone Starts

We will see in details about BroadCast Receivers with the Example in coming tutorials.

Broadcast Receivers can be defined in the Manifest.xml as the below mentioned code.

<receiver android:name=".YourReceiver">

<intent-filter>

<action android:name="android.intent.action.BATTERY_LOW" />

</intent-filter>

</receiver>

Intent:

Intents are messages that allow components to request activities from other components. Consider an activity requires another activity to perform some functionality in such cases communication between activities occurs via Intent.

We will see in details about Intent Class with the Example in coming tutorials.

There are two types of Intents in Android:

Explicit Intents:

In explicit Intent, we are highly specific. We specify which activity should get active on receiving the intent. These are usually used for application’s internal communications.

Implicit Intents:

In implicit Intent we are sending a message to the Android system to find a suitable Activity that can respond to the intent. For example, to send an e-mail, we can use an intent. We will also specify  the data to be operated on, with the intent. On receiving the Intent, Android system will invoke an Activity which is able to send e-mail messages with the data that we specified. If there is more than one activity is capable of receiving the Intent, the system presents a chooser to the user so that he can select which Activity/Application should handle it.

 Android Components with Twitter Example:

Please Send Your Comments To ambilpura.sunil@gmail.com

NEXT Tutorial:  What Is Emulator and How Can We Create Emulator