Android Notes: Lessons from HelloWorld

Basic Setup

• Install Android Studio
• Get the required SDK - I got the latest SDK for 4.4
• Gradle build tool is bundled with Android Studio? (Maybe, I don't know)
• Create the Android Virtual Devices (emulator) for testing - use the AVD manager (the AVD manager can also be launched from inside Android Studio, as can the SDK Manager)
• You may need to install the correct CPU/ABI for the emulator from the SDK Manager.
• Launch the AVD - you will probably need to set the RAM on the emulator to a low value (200MB) for the device emulator to launch in a decent time. 

Basic development process

• Write code - target a particular version of the Android SDK
• Launch emulator
• Run code. this will:  
• compile and create an APK
• install the APK in the emulator
• launch the app

Structure of an Android HelloWorld App

public class Greetings extends Activity 

• An Activity represents a screen in the UI
• Contains a bunch of on* methods (onCreate, onCreateOptionsMenu, ...) which will be invoked when specific events happen.

AndroidManifest.xml

• Declares various components (including Activities) which are to be a part of the application.
• Various important pieces:
• uses-sdk  - which sdk the application can work with (max, min,...)
• application - defines the application, contains the various components like activities, services, etc.
• activity (inside application) - defines a screen
• intent-filter (inside activity, can it be in other places?) - defines what events the activity will listen for?

The res/ Directory

• Contains various resources needed by the application
• drawable-* : different images to be drawn, based on screen resolution
• layout - contains layouts for various activities - how to layout the screen
• menu?
• values/strings.xml - different strings to be used in the application

R  Generated class

• Generated during build - do not hand edit. 
• Contains various strings/resources/etc. - can be used in the application.