Android - Important Android components


Important Android components
An Android application consists out of the following parts:
  • Activity - Represents the presentation layer of an Android application, e.g. a screen which the user sees. An Android application can have several activities and it can be switched between them during runtime of the application.
  • Views - The User interface of an Activities is build with widgets classes which inherent from "android.view.View". The layout of the views is managed by android.view.ViewGroups".
  • Services - perform background tasks without providing an UI. They can notify the user via the notification framework in Android.
  • Content Provider - provides data to applications, via a content provider your application can share data with other applications. Android contains a SQLite DB which can serve as data provider
  • Intents are asynchronous messages which allow the application to request functionality from other services or activities. An application can call directly a service or activity (explicit intent) or ask the Android system for registered services and applications for an intent (implicit intents). For example the application could ask via an intent for a contact application. Application register themself to an intent via an IntentFilter. Intents are a powerful concept as they allow to create loosely coupled applications.
  • Broadcast Receiver - receives system messages and implicit intents, can be used to react to changed conditions in the system. An application can register as a broadcast receiver for certain events and can be started if such an event occurs.
Other Android parts are Android Widgets or Live Folders and Live Wallpapers . Live Folders display any source of data on the homescreen without launching the corresponding application.

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