MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

What We’ve Just Learned
• Statefulness is important to Windows Store apps, to maintain a sense of continuity between
sessions even if the app is suspended and terminated.
• App data is session, local, temporary, and roaming state that is tied to the existence of an app; it
is accessible only by that app.
• User data is stored in locations other than app data (such as the user’s music, pictures, videos,
and documents libraries, along with removable storage) and persists independent of any given
app, and multiple apps might be able to open and manipulate user files.
• App data is accessed through the Windows.Storage.ApplicationData API and accommodates
both structured settings containers as well as file-based data. Additional APIs like IndexedDB and
HTML5 localStorage are also available.
• It is important to version app state, especially where roaming is concerned, as versioning is how
the roaming service manages what app state gets roamed to which devices based on what
version apps are looking for.
• The size of roaming state is limited to a quota (provided by an API), otherwise Windows will not
roam the data. Services like SkyDrive can be used to roam larger files, including user data.
• The typical roaming period is 30 minutes or less. A single setting or composite named
“HighPriority,” so long as it’s under 8K, will be roamed within a minute.
• The StorageFolder and StorageFile classes in WinRT are the core objects for working with
folders and files. All programmatic access to the file system begins, in fact, with a StorageFolder.
Otherwise, the user can point to files and folders through the file picker API, which is really the
first choice for file access.
• Blobs are useful aids in working with files, as are the WinRT APIs in the Windows.Storage.-
FileIO and PathIO classes. WinJS offers some simplified methods for reading and writing text
files (especially in conjunction with app state), and the HTML5 FileReader is supported.
• WinRT offers encryption services through Windows.Security.Cryptography, as well as a built-in
compression mechanism in Windows.Storage.Compression.
• To use the Settings pane, an app populates the top-level pane provided by Windows with
specific commands. Those commands map to handlers that either open a hyperlink (in a
browser) or display a settings flyout using the WinJS.UI.SettingsFlyout control. Those flyouts
can contain any HTML desired, including iframe elements that load remote content.
• Access to user data folders, such as media libraries, documents, and removable storage, is
controlled by manifest capabilities. Such capabilities need be declared only if the app needs to
access the file system in some way other than using the file picker.
361