1. Storage Access Framework

　　Android 4.4 (API level 19) introduces the Storage Access Framework (SAF). The SAF makes it simple for users to browse and open

　　　　documents, images, and other files across all of their their preferred document storage providers. A standard, easy-to-use UI lets

　　　　users browse files and access recents in a consistent way across apps and providers.

2. Overview

3. Control Flow

　　Here shows an example of how a photo app might use the SAF to access stored data:

　　In the SAF, providers and clients don‘t interact directly. A client requests permission to interact with files (that is, to read, edit, create, or

　　　　delete files).
　　The interaction starts when an application (in this example, a photo app) fires the intent ACTION_OPEN_DOCUMENT or

　　　　ACTION_CREATE_DOCUMENT. The intent may include filters to further refine the criteria—for example, "give me all openable files that

　　　　have the ‘image‘ MIME type."

　　Once the intent fires, the system picker goes to each registered provider and shows the user the matching content roots.

　　The picker gives users a standard interface for accessing documents, even though the underlying document providers may be very different.

　　For example, figure above shows a Google Drive provider, a USB provider, and a cloud provider.

4. Writing a Client App

2.App Components-Content Providers/Storage Access Framework