Storing Local Data

So far, we've concentrated on writing applications that don't need to keep data around when they exit. They start up, run, and go away, leaving no trace that they were ever there. However, most real programs need persistent state, whether it's a simple font size setting, an embarrassing photo from your last office party, or next week's meal plan. Whatever it is, Android lets you permanently store it on your mobile device for later use and protects it from accidental or malicious access by other programs.

Your application can store data using several different techniques depending on the size of the data, its structure, its lifetime, and whether it will be shared with other programs. In this chapter, we'll take a look at three simple methods to keep local data: the preferences API, instance state bundles, and flash memory files. In Chapter 9, Putting SQL to Work, on page 178, we'll delve into more advanced techniques using the built-in SQLite database engine.

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