Professional Android, 4th Edition

8Files, Saving State, and User Preferences

WHAT'S IN THIS CHAPTER?

• Persisting application data using Shared Preferences
• Managing application settings and building Preference Screens
• Saving Activity instance data between sessions
• Using View Models and Live Data
• Including static files as external resources
• Saving and loading files, and managing the local filesystem
• Using the application file caches
• Storing files in public directories
• Sharing files between applications
• Accessing files from other applications

WROX.COM CODE DOWNLOADS FOR THIS CHAPTER

The code downloads for this chapter are found at www.wrox.com. The code for this chapter is divided into the following major examples:

• Snippets_ch8.zip
• Earthquake_ch8.zip

SAVING FILES, STATES, AND PREFERENCES

This chapter introduces some of the simplest and most versatile data-persistence and file sharing techniques in Android: Shared Preferences, instance-state Bundles, local files, and the Storage Access Framework.

At a minimum, an Activity should save its user interface (UI) state before becoming inactive, to ensure the same UI is presented when the Activity restarts. It’s also likely that you’ll need to save user preferences and UI selections.

Android’s nondeterministic Activity and application lifetimes make persisting UI state and application data between sessions particularly important, because your application process may have been killed and restarted before it returns to the foreground.

We will explore mechanisms ...