Android Application Component

• Asynchronous Message

intent/intent filter

• Activities, services, and broadcast receivers are activated by asynchronous messages called intents.

• intent
  • asynchronous messages/an abstract description of an operation to be performed
  • Intent object
    • holds the content of the message
    • Component name
    • Action
    • Data
      • The URI of the data to be acted on and the MIME type of that data
    • Category

• activating
  • activity
    • Context.startActivity()
    • Activity.startActivityForResult()
  • service
    • Context.startService()
    • Context.bindService()
  • broadcast receiver
    • Context.sendBroadcast()
    • Context.sendOrderedBroadcast()
    • Context.sendStickyBroadcast()

• intent resolution
  • action
  • data (both URI and data type)
  • category

• IntentFilter
  • Action test
    • Intent object must match one of the actions listed in the filter
  • Category test
    • an Intent object with no categories should always pass this test
    • implicit intents contained at least one category: android.intent.category.DEFAULT
  • Data test
    • URI
      • scheme://host:port/path
      • When the URI in an Intent object is compared to a URI specification in a filter, it's compared only to the parts of the URI actually mentioned in the filter
    • type

• OpenIntents
  • Open Intents - Android Intents Mechanism and Dependency Management

• Intent and Intent Filter, Broadcast Receivers

Bundles

• typesafe containers of primitives
• A mapping from String keys to various Parcelable types values.

• Activity

Activity

• a visual user interface
• Activity class

• Activity vs. Window
  • Each activity is given a default window to draw in
  • An activity can also make use of additional windows

• activity stack

Activity Lifecycle

• Starting up phase
  • (entire lifetime)onCreate()
    • first method called during lifetime, with prior state
    • Called when the activity is first created
    • This method also provides you with a Bundle containing the activity's previously frozen state, if there was one
  • (visible lifetime)onStart()/onRestart()
    • signal that execution is beginning
    • Called when the activity is becoming visible to the user
  • (foreground lifetime)onResume()
    • signals that a previous pause is being undone
    • Called when the activity will start interacting with the user
    • At this point your activity is at the top of the activity stack.

• Normal execution phase
  • (foreground lifetime)onPause
    • signals loss of focus and possible impending shutdown
    • typically used to commit unsaved changes to persistent data, stop animations and other things that may be consuming CPU.
    • it is important to save persistent data in onPause() instead of onSaveInstanceState(Bundle) because the later is not part of the lifecycle callbacks
  • onSaveInstanceState(Bundle) is called before the activity is killed, allowing you to save away any dynamic instance state in your activity into the given Bundle, to be later received in onCreate(Bundle) if the activity needs to be re-created.
    • This method is called before an activity may be killed so that when it comes back some time in the future it can restore its state.

• Shutting down phase
  • (visible lifetime)onStop()
    • Called when the activity is no longer visible to the user
  • (entire lifetime)onDestroy()
    • final shutdown and process termination
    • The final call you receive before your activity is destroyed.
    • Not guaranteed to be called (and usually not, except on finish()…)

• Service

Service

• doesn't have a visual user interface, but rather runs in the background for an indefinite period of time
• Implementing a Download Background Service

Service Lifecycle

• Broadcast Receiver

Broadcast Receiver

• receive and react to broadcast announcements

Broadcast Receiver Lifecycle

• Content Provider

Content Provider

• a specific set of the application's data
• Content providers are activated when they're targeted by a request from a ContentResolver.

ContentResolver

• getContentResolver()

• Query
  • ContentResolver.query()
  • Activity.managedQuery(URI, The names of the data columns that should be returned, SQL WHERE clause, Selection arguments, SQL ORDER BY clause)

URI

• ContentUris.withAppendedId
• Uri.withAppendedPath

Cursor

• Activity.startManagingCursor()