File I/O in Windows Runtime

The following obtains a directory listing of all files in the documents folder:
StorageFolder docsFolder = KnownFolders.DocumentsLibrary;
IReadOnlyList<StorageFile> files = await docsFolder.GetFilesAsync();
foreach (IStorageFile file in files)
Debug.WriteLine (file.Name);

The CreateFileQueryWithOptions method lets you filter to a specific extension:
StorageFolder docsFolder = KnownFolders.DocumentsLibrary;
var queryOptions = new QueryOptions (CommonFileQuery.DefaultQuery,
new[] { ".txt" });
var txtFiles = await docsFolder.CreateFileQueryWithOptions (queryOptions)
.GetFilesAsync();
foreach (StorageFile file in txtFiles)
Debug.WriteLine (file.Name);

The QueryOptions class exposes properties to further control the search. For example,
the FolderDepth property requests a recursive directory listing:
queryOptions.FolderDepth = FolderDepth.Deep;

For example, the  following creates and writes to a file called test.txt in the documents folder:
StorageFolder docsFolder = KnownFolders.DocumentsLibrary;
StorageFile file = await docsFolder.CreateFileAsync
("test.txt", CreationCollisionOption.ReplaceExisting);
using (Stream stream = await file.OpenStreamForWriteAsync())
using (StreamWriter writer = new StreamWriter (stream))
await writer.WriteLineAsync ("This is a test");
If you don’t specify CreationCollisionOption.ReplaceExisting
and the file already exists, it will automatically append a number
to the filename to make it unique.
The following reads the file back:
StorageFolder docsFolder = KnownFolders.DocumentsLibrary;
StorageFile file = await docsFolder.GetFileAsync ("test.txt");
using (var stream = await file.OpenStreamForReadAsync ())
using (StreamReader reader = new StreamReader (stream))
Debug.WriteLine (await reader.ReadToEndAsync());

Isolated Storage in Metro Apps Metro apps also have access to private folders that are isolated from other applications and can be used to store application-specific data:
Windows.Storage.ApplicationData.Current.LocalFolder
Windows.Storage.ApplicationData.Current.RoamingFolder
Windows.Storage.ApplicationData.Current.TemporaryFolder
Each of these static properties returns a StorageFolder object which can be used to read/write and list files as we described previously.