HTML and CSS Reference
In-Depth Information
Chapter 10
Adding persistent data to
applications
—Stephen Hawking
No applications that are expected to be more than just a basic exercise can operate without persis-
tent data. As users work with the application, they produce information by entering fresh data or
processing known values. This information will not be lost with the shutdown of the application. This
information is vital and must be persisted somewhere to be reloaded on the next session or on demand.
To make data persistent, software uses files; sometimes applications make use of very special
files known as
databases
. A database is ultimately a large collection of files owned and managed by
a specific and distinct application. Interacting with a database is more expensive in terms of system
resources since it involves ad hoc protocols for an app-to-app communication.
In this chapter, you won't use any database, but you will go through a number of exercises that
involve files. In particular, you'll be extending the TodoList application to make it able to save tasks
to files and reload them on demand. In doing so, you will also learn a lot about the application
programming interface (API) available to Windows Store applications to deal with persistent data.
Persisting application objects
The first exercise of this chapter consists of taking the version of the TodoList application you worked
on in the last chapter one step further. You will enable the application to pick a file and save some of
the details of the task to it.
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