Android Basics

Android History

2003	Andy Rubin Founded Android
2005	Google buys Android, Inc. Work on Dalvik starts
2007	OHA Announced Early SDK
2008	First Android Phone G1 Announced SDK 1.0 Released
2009	Cupcake(1.5), Donut(1.6), Éclair(2.0) versions of Android Released.
2010	2.1 and Froyo(2.2) Released

Android and Java

Dalvik Virtual Machine

• Its Free 
• Originally written by Dan Bornstein at Google 
• Register-based   Vs   stack-based Java VM 
• Highly CPU optimized Bytecode Interpretor 
• Uses Runtime memory very efficiently 
• Highly Compact 
• Different set of Java Libs than SDK 

Activity


An activity is like a self contained use case. As per Android, it is a single, focused thing that the user can do. Almost all activities interact with the user, so the Activity class takes care of creating a window for you in which you can place your UI with setContentView(View). 


Intent


An intent is an abstract description of an operation to be performed. They can be implicit and explicit.

Services

A service is something that can be started and stopped. It doesn’t have UI. It is typically managed by an activity. 

Content Providers

Content Providers share content with applications across application boundaries. This would be useful if you are creating multiple apps with shared content.

Manifest File 

1. The Android Manifest file describes your application to the Android OS 
2. Every Application needs to have “AndroidManifest.xml (WITH PRECICELY THAT NAME) in its root dir. 
3. It describes components like Activities, Services, BroadcastReceivers, Content Providers and Classes that implement these components. 
4. Permissions that the Application needs should be declared in here 
5. Permissions that other Applications are required to have in order to interact with the application’s components.

XML-Based User Interface

Android provides a straightforward XML vocabulary that corresponds to the View classes and subclasses. You can use the WYSIWYG tools in Eclipse to build powerful XML-based UI. Check out this link for more details:

http://developer.android.com/guide/topics/ui/declaring-layout.html