MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

scenario oriented on the music library that lets you enter in an AQS string directly. However, this isn’t
always what you’ll be using in an app, so I wanted to show many other variations.
Queries always start with a StorageFolder, whose createFileQuery[WithOptions],
createFolderQuery[WithOptions], and createItemQuery[WithOptions] methods (6 total) provide for
enumerating files, folders, or both, within whatever folder the StorageFolder is attached to. The
simplest queries are created with the base StorageFolder.create* methods and no parameters:
folder.createFileQuery();
folder.createFolderQuery();
folder.createItemQuery();
The first two methods here are actually just shortcuts for the one-parameter variants with the same
names, where that parameter is a value from the Windows.Storage.Search.CommonFileQuery or
CommonFolderQuery enumerations. These shortcut versions just use the defaultQuery value for a simple
alphabetical, shallow enumeration of the folder contents. createItemQuery, for its part, has only this one
form.
Creating a query itself doesn’t actually enumerate anything until you ask it to through an async
method: for file queries the method is getFilesAsync, for folders it’s getFoldersAsync, and for items it’s
getItemsAsync. (See a pattern here?) So, in Scenario 2 of the FileQuery example, I have these three
functions attached to buttons:
function fileQuery() {
var query = picturesLibrary.createFileQuery();
SdkSample.showResults(query.getFilesAsync());
}
function folderQuery() {
var query = picturesLibrary.createFolderQuery();
SdkSample.showResults(query.getFoldersAsync());
}
function itemQuery() {
var query = picturesLibrary.createItemQuery();
SdkSample.showResults(query.getItemsAsync());
}
where the SdkSample.showResults function in js/default.js just creates a listing of the items in the
collection. Running this sample, you’ll see a list of those files and/or folders in your Pictures library.
Tip The actual object types returned by these create*Query APIs are StorageFileQueryResult,
StorageFolderQueryResult, and StorageItemQueryResult, all in the Windows.Storage.Search
namespace. These all provide some additional properties like folder, methods like
findStartIndexAsync and getItemCountAsync, and events like optionschanged and
contentschanged (both WinRT events). The latter event especially is something you can use to monitor
changes to the file system that affect query results.
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