GetQuery Method

BitmapMetadata.GetQuery Method (String)

 

Provides access to a metadata query reader that can extract metadata from a bitmap image file.

Namespace:   System.Windows.Media.Imaging
Assembly:  PresentationCore (in PresentationCore.dll)

<SecurityCriticalAttribute>
Public Function GetQuery (
	query As String
) As Object

Parameters

query
Type: System.String

Identifies the string that is being queried in the current BitmapMetadata object.

Return Value

Type: System.Object

The metadata at the specified query location.

Exception Condition
ArgumentNullException

query is null.

Metadata that is associated with an image is data that describes the image but that is not necessary for display of the image. Each supported bitmap image format handles metadata differently, but the facility for reading and writing metadata is the same.

Windows Presentation Foundation (WPF) supports the following image metadata schemas: Exchangeable image file (Exif), tEXt (PNG Textual Data), image file directory (IFD), International Press Telecommunications Council (IPTC), and Extensible Metadata Platform (XMP).

The following code example demonstrates how to use the SetQuery method to write metadata to a Portable Network Graphics (PNG) file.

Dim pngStream As New System.IO.FileStream("smiley.png", FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite)
Dim pngDecoder As New PngBitmapDecoder(pngStream, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default)
Dim pngFrame As BitmapFrame = pngDecoder.Frames(0)
Dim pngInplace As InPlaceBitmapMetadataWriter = pngFrame.CreateInPlaceBitmapMetadataWriter()
If pngInplace.TrySave() = True Then
    pngInplace.SetQuery("/Text/Description", "Have a nice day.")
End If
pngStream.Close()

After the metadata is written, the GetQuery method is used to read that data and emit it as a text string.

' Add the metadata of the bitmap image to the text block.
Dim myTextBlock As New TextBlock()
myTextBlock.Text = "The Description metadata of this image is: " + pngInplace.GetQuery("/Text/Description").ToString()

.NET Framework
Available since 3.0
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