Professional Android 4 Application Development, 3rd Edition

Chapter 7

Files, Saving State,and Preferences

What's in this Chapter?

Persisting simple application data using Shared Preferences

Saving Activity instance data between sessions

Managing application preferences and building Preference Screens

Saving and loading files and managing the local filesystem

Including static files as external resources

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

Saving and loading data is essential for most applications. At a minimum, an Activity should save its user interface (UI) state before it becomes inactive to ensure the same UI is presented when it 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, as your application process may have been killed and restarted before it returns to the foreground. Android offers several alternatives for saving application data, each optimized to fulfill a particular need.

Shared Preferences are a simple, lightweight name/value pair (NVP) mechanism for saving primitive application data, most commonly a user's application preferences. Android also offers a mechanism for recording application state within the Activity lifecycle handlers, as well as for providing access to the local filesystem, through both specialized ...