ファイル アクセスの最適化

StorageFolder library = Windows.Storage.KnownFolders.PicturesLibrary;
IReadOnlyList<StorageFile> files = await library.GetFilesAsync(Windows.Storage.Search.CommonFileQuery.OrderByDate);

for (int i = 0; i < files.Count; i++)
{
    // do something with the name of each file
    string fileName = files[i].Name;
}

Dim library As StorageFolder = Windows.Storage.KnownFolders.PicturesLibrary
Dim files As IReadOnlyList(Of StorageFile) =
    Await library.GetFilesAsync(Windows.Storage.Search.CommonFileQuery.OrderByDate)

For i As Integer = 0 To files.Count - 1
    ' do something with the name of each file
    Dim fileName As String = files(i).Name
Next i

StorageFolder library = Windows.Storage.KnownFolders.PicturesLibrary;
IReadOnlyList<StorageFile> files = await library.GetFilesAsync(Windows.Storage.Search.CommonFileQuery.OrderByDate);
for (int i = 0; i < files.Count; i++)
{
    ImageProperties imgProps = await files[i].Properties.GetImagePropertiesAsync();

    // do something with the date the image was taken
    DateTimeOffset date = imgProps.DateTaken;
}

Dim library As StorageFolder = Windows.Storage.KnownFolders.PicturesLibrary
Dim files As IReadOnlyList(Of StorageFile) = Await library.GetFilesAsync(Windows.Storage.Search.CommonFileQuery.OrderByDate)
For i As Integer = 0 To files.Count - 1
    Dim imgProps As ImageProperties =
        Await files(i).Properties.GetImagePropertiesAsync()

    ' do something with the date the image was taken
    Dim dateTaken As DateTimeOffset = imgProps.DateTaken
Next i

// Set QueryOptions to prefetch our specific properties
var queryOptions = new Windows.Storage.Search.QueryOptions(CommonFileQuery.OrderByDate, null);
queryOptions.SetThumbnailPrefetch(ThumbnailMode.PicturesView, 100,
        ThumbnailOptions.ReturnOnlyIfCached);
queryOptions.SetPropertyPrefetch(PropertyPrefetchOptions.ImageProperties, 
       new string[] {"System.Size"});

StorageFileQueryResult queryResults = KnownFolders.PicturesLibrary.CreateFileQueryWithOptions(queryOptions);
IReadOnlyList<StorageFile> files = await queryResults.GetFilesAsync();

foreach (var file in files)
{
    ImageProperties imageProperties = await file.Properties.GetImagePropertiesAsync();

    // Do something with the date the image was taken.
    DateTimeOffset dateTaken = imageProperties.DateTaken;

    // Performance gains increase with the number of properties that are accessed.
    IDictionary<String, object> propertyResults =
        await file.Properties.RetrievePropertiesAsync(
              new string[] {"System.Size" });

    // Get/Set extra properties here
    var systemSize = propertyResults["System.Size"];
}

' Set QueryOptions to prefetch our specific properties
Dim queryOptions = New Windows.Storage.Search.QueryOptions(CommonFileQuery.OrderByDate, Nothing)
queryOptions.SetThumbnailPrefetch(ThumbnailMode.PicturesView,
            100, Windows.Storage.FileProperties.ThumbnailOptions.ReturnOnlyIfCached)
queryOptions.SetPropertyPrefetch(PropertyPrefetchOptions.ImageProperties,
                                 New String() {"System.Size"})

Dim queryResults As StorageFileQueryResult = KnownFolders.PicturesLibrary.CreateFileQueryWithOptions(queryOptions)
Dim files As IReadOnlyList(Of StorageFile) = Await queryResults.GetFilesAsync()


For Each file In files
    Dim imageProperties As ImageProperties = Await file.Properties.GetImagePropertiesAsync()

    ' Do something with the date the image was taken.
    Dim dateTaken As DateTimeOffset = imageProperties.DateTaken

    ' Performance gains increase with the number of properties that are accessed.
    Dim propertyResults As IDictionary(Of String, Object) =
        Await file.Properties.RetrievePropertiesAsync(New String() {"System.Size"})

    ' Get/Set extra properties here
    Dim systemSize = propertyResults("System.Size")

Next file

StorageFile file = await Windows.Storage.ApplicationData.Current
    .LocalFolder.GetFileAsync("example.txt");
Windows.Storage.Streams.IInputStream windowsRuntimeStream = 
    await file.OpenReadAsync();

byte[] destinationArray = new byte[8];

// Create an adapter with the default buffer size.
using (var managedStream = windowsRuntimeStream.AsStreamForRead())
{

    // Read 8 bytes into destinationArray.
    // A larger block is actually read from the underlying 
    // windowsRuntimeStream and buffered within the adapter.
    await managedStream.ReadAsync(destinationArray, 0, 8);

    // Read 8 more bytes into destinationArray.
    // This call may complete much faster than the first call
    // because the data is buffered and no call to the 
    // underlying windowsRuntimeStream needs to be made.
    await managedStream.ReadAsync(destinationArray, 0, 8);
}

Dim file As StorageFile = Await Windows.Storage.ApplicationData.Current -
.LocalFolder.GetFileAsync("example.txt")
Dim windowsRuntimeStream As Windows.Storage.Streams.IInputStream =
    Await file.OpenReadAsync()

Dim destinationArray() As Byte = New Byte(8) {}

' Create an adapter with the default buffer size.
Dim managedStream As Stream = windowsRuntimeStream.AsStreamForRead()
Using (managedStream)

    ' Read 8 bytes into destinationArray.
    ' A larger block is actually read from the underlying 
    ' windowsRuntimeStream and buffered within the adapter.
    Await managedStream.ReadAsync(destinationArray, 0, 8)

    ' Read 8 more bytes into destinationArray.
    ' This call may complete much faster than the first call
    ' because the data is buffered and no call to the 
    ' underlying windowsRuntimeStream needs to be made.
    Await managedStream.ReadAsync(destinationArray, 0, 8)

End Using

MemoryStream destination = new MemoryStream();
// copies the buffer into memory using the default copy buffer
await managedStream.CopyToAsync(destination);

// Copy the buffer into memory using a 1 MB copy buffer.
await managedStream.CopyToAsync(destination, bufferSize: 1024 * 1024);

Dim destination As MemoryStream = New MemoryStream()
' copies the buffer into memory using the default copy buffer
Await managedStream.CopyToAsync(destination)

' Copy the buffer into memory using a 1 MB copy buffer.
Await managedStream.CopyToAsync(destination, bufferSize:=1024 * 1024)