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How Content Providers Work

  • Article

There are two classes involved in a ContentProvider interaction:

  • ContentProvider – Implements an API that exposes a set of data in a standard way. The main methods are Query, Insert, Update and Delete.

  • ContentResolver – A static proxy that communicates with a ContentProvider to access its data, either from within the same application or from another application.

A content provider is normally backed by an SQLite database, but the API means that consuming code does not need to know anything about the underlying SQL. Queries are done via a Uri using constants to reference column names (to reduce dependencies on the underlying data structure), and an ICursor is returned for the consuming code to iterate over.

Consuming a ContentProvider

ContentProviders expose their functionality through a Uri that is registered in the AndroidManifest.xml of the application that publishes the data. There is a convention where the Uri and the data columns that are exposed should be available as constants to make it easy to bind to the data. Android's built-in ContentProviders all provide convenience classes with constants that reference the data structure in the Android.Providers namespace.

Built-In Providers

Android offers access to a wide range of system and user data using ContentProviders:

  • Browser – bookmarks and browser history (requires permission READ_HISTORY_BOOKMARKS and/or WRITE_HISTORY_BOOKMARKS).

  • CallLog – recent calls made or received with the device.

  • Contacts – detailed information from the user's contact list, including people, phones, photos & groups.

  • MediaStore – contents of the user's device: audio (albums, artists, genres, playlists), images (including thumbnails) & video.

  • Settings – system-wide device settings and preferences.

  • UserDictionary – contents of the user-defined dictionary used for predictive text input.

  • Voicemail – history of voicemail messages.

Classes Overview

The primary classes used when working with a ContentProvider are shown here:

Class diagram of Content Provider application and Consuming application interactions

In this diagram, the ContentProvider implements queries and registers URI's that other applications use to locate data. The ContentResolver acts as a 'proxy' to the ContentProvider (Query, Insert, Update, and Delete methods). The SQLiteOpenHelper contains data used by the ContentProvider, but it is not directly exposed to consuming apps. The CursorAdapter passes the cursor returned by the ContentResolver to display in a ListView. The UriMatcher is a helper class that parses URIs when processing queries.

The purpose of each class is described below:

  • ContentProvider – Implement this abstract class's methods to expose data. The API is made available to other classes and applications via the Uri attribute that is added to the class definition.

  • SQLiteOpenHelper – Helps implement the SQLite datastore that is exposed by the ContentProvider.

  • UriMatcher – Use UriMatcher in your ContentProvider implementation to help manage Uris that are used to query the content.

  • ContentResolver – Consuming code uses a ContentResolver to access a ContentProvider instance. The two classes together take care of the inter-process communication issues, allowing data to be easily shared between applications. Consuming code never creates a ContentProvider class explicity; instead, the data is accessed by creating a cursor based on a Uri exposed by the ContentProvider application.

  • CursorAdapter – Use CursorAdapter or SimpleCursorAdapter to display data accessed via a ContentProvider.

The ContentProvider API allows consumers to perform a variety of operations on the data, such as:

  • Query data to return lists or individual records.
  • Modify individual records.
  • Add new records.
  • Delete records.

This document contains an example that uses a system-provided ContentProvider, as well as a simple read-only example that implements a custom ContentProvider.