Activity

• Single screen
• Extends Activity base class
• UI composed of Views (rectangular area on screen that is responsible for drawing and event handling)
• Responds to events
• Change screens by starting new Activity
  -via an Intent
  • abstract description of action to perform
  • launches Activities; acts as glue between Activities
  • consists of action to do and data

Broadcast Intent Receiver

• Good for reactions to an external event (phone rings, data network is available, it's 12:00)
• Use Notification Manager to alert user if something happened
• Registered in AndroidManifest.xml or by using Context.registerReceiver()
• Application need not be running! System can start applications when needed.
• Applications can also send own intent broadcasts (Context.sendBroadcast())

Service

• Runs without UI (example: media player automatically and continuously playing songs from playlist in background)
• Long-lived
• Started by Context.startService() or called by Context.bindService()
• Communicate with via interface exposed by service (example: pause, rewind, etc)

Content Provider

• Useful if you want to share data with other apps
• Class that implements a standard set of methods to let other applications store and retrieve the type of data handled by Content Provider