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Introduction to Android | Android Developers



・single screen 
・Apps adapt to different devices
・assigns each app a unique Linux user ID
・Each process has its own VM, so an app's code runs in isolation from other apps.


・One APK file contains all the contents of an Android app


・All app permissions must be granted by the user at install time


Intents and Intent Filters * アプリケーション間の呼び出し

・action that other apps may invoke(start another app using an intent)
・combination of distinct components(start another component using an intent)
  • 外部URL呼び出し
an intent might convey a request for an activity to show an image or to open a web page. 


・service(work in the background)


  • Activities
An activity represents a single screen with a user interface.
  • Services
A service is a component that runs in the background
to perform long-running operations or to perform work for remote processes.
  • Content providers
A content provider manages a shared set of app data.

You can store the data in the file system, an SQLite database, on the web,
or any other persistent storage location your app can access.

other apps can query or even modify the data

content provider, is not activated by intents.
Rather, it is activated when targeted by a request from a ContentResolver
  • Broadcast receivers
A broadcast receiver is a component responds to system-wide broadcast announcements.



<activity> elements for activities
<service> elements for services
<receiver> elements for broadcast receivers
<provider> elements for content providers


If your app starts the activity in the camera app that captures a photo,
that activity runs in the process that belongs to the camera app, not in your app's process. 


you should define animations, menus, styles, colors,
and the layout of activity user interfaces with XML files.

the SDK build tools define a unique integer ID, which you can use to reference the resource from your app code or from other resources defined in XML