What is an Android?

What is an Android?

This is posts describes you about the four main components of Android. This will be useful for people who like to learn about the basics of Android. Read further U ll find it useful too...

Activity:

An activity represents the visual representation of an Android application.

 User interacts with the screen provided by the activity. 

Typically, an activity hosts a view, which can be an application-specific view or a system-provided view. activities use views.  

An activity is associated with a window and covers the entire screen.   

An application needs to have at least one main activity to start but can have a number of other activities—roughly one per screen.  

Activities are organized in a stack and when a new activity starts, it goes to the top of the stack.  

Users can then navigate through the stack using the Back button.

Activities receive notification from the system about relevant facts during their lifetime.  

For example, activities can be notified when they are pushed to the background and restored.

Services: 

A service is a UI-less component that runs in the background.

It involves in the tasks such as uploading or downloading data and application-specific calculations. 

A service is normally started by an activity.

Broadcast Receivers: 

A broadcast receiver listens to special messages being broadcast by the system or individual applications. 

An interesting example of a broadcast message is a network-state-change that is sent out when we get or lose connectivity. Similarly messages can be received when the connectivity changes from Wi-Fi to 3G, the battery is dangerously low, or an SMS message is received. 

Applications can also broadcast. 

A receiver is often UI-less but can display notifications on the status bar.  

Content Providers: 

A content provider is a component that manages shared data and optionally exposes query and update capabilities for other components to invoke.

An example is the provider for data about the contacts you have stored in the phone. One piece of information that you often need to add to a manifest file is the list of permissions

Views and layout manager

Views are user interface widgets, e.g. buttons or text fields. The base class for all views is the android.view.Viewclass.

Views have attributes which can be used to configure their appearance and behavior.

A layout manager is responsible for arranging other views. 

The base class for these layout managers is theandroid.view.ViewGroup class which extends the View class.

Layout managers can be nestled to create complex layouts.

Live Wallpapers

 It allows to create animated wallpapers on Android home screen.