GetInformationAsync(Stream,Boolean,Int32,Object) Method

Gets the image information from a stream containing image data asynchronously.

Syntax

Visual Basic
C#
WinRT C#
WinRT JavaScript
C++

public CodecsImageInfo GetInformationAsync( 
   Stream stream,
   bool totalPages,
   int pageNumber,
   object userState
)

'Declaration
 
Public Overloads Function GetInformationAsync( _
   ByVal stream As Stream, _
   ByVal totalPages As Boolean, _
   ByVal pageNumber As Integer, _
   ByVal userState As Object _
) As CodecsImageInfo

'Usage
 
Dim instance As RasterCodecs
Dim stream As Stream
Dim totalPages As Boolean
Dim pageNumber As Integer
Dim userState As Object
Dim value As CodecsImageInfo
 
value = instance.GetInformationAsync(stream, totalPages, pageNumber, userState)

public CodecsImageInfo GetInformationAsync( 
   Stream stream,
   bool totalPages,
   int pageNumber,
   object userState
)

 function Leadtools.Codecs.RasterCodecs.GetInformationAsync(Stream,Boolean,Int32,Object)( 
   stream ,
   totalPages ,
   pageNumber ,
   userState 
)

public:
CodecsImageInfo^ GetInformationAsync( 
   Stream^ stream,
   bool totalPages,
   int pageNumber,
   Object^ userState
)

Parameters

stream: System.IO.Stream containing the input image data to query.
totalPages: true to query the file for total number of pages; false, otherwise.
pageNumber: The page number to query. Pass 1 for the first page (default).
userState: A user-defined object that is passed to the method invoked when the asynchronous operation completes.

Return Value

A CodecsImageInfo object that contains the information about the specified image. See remarks about the usage of this object.

Remarks

Specifying true for totalPages can cause the process to be slow for files with large number of pages.

The RasterCodecs class supports getting information on image files asynchronously using the GetInformationAsync methods. When calling any of these methods, the caller thread will not be blocked and the method will return instantly with an instance CodecsImageInfo that is in a loading status (CodecsImageInfo.IsLoading set to true). You should not use the other properties of this object while the object is in loading status.

When the RasterCodecs object finishes getting the information about the file, the various properties of the CodecsImageInfo will be populated with the image file information and the CodecsImageInfo.IsLoading property will be set to false.

It is recommended that you do not poll for the CodecsImageInfo.IsLoading property to determine whether the image information has been collected. Instead, subscribe to the GetInformationAsyncCompleted event to get notification on when the GetInformationAsync(String,Boolean,Int32,Object) operation is completed and whether any errors occurred.

The GetInformationAsyncCompleted event data will also contain the same object returned from GetInformationAsync so you do not have to keep the original object in your application.

userState will be passed to the CodecsGetInformationAsyncCompletedEventArgs.UserState member of the GetInformationAsyncCompleted event data.

Example

Visual Basic
C#
WinRT C#
WinRT JavaScript
Silverlight C#
Silverlight VB

Public Sub GetInformationAsyncStreamExample()
      Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp")

      Dim codecs As New RasterCodecs()

      ' Now get information about the file asynchronously
      AddHandler codecs.GetInformationAsyncCompleted, AddressOf GetInformationAsyncStreamExample_GetInformationAsyncCompleted

      Dim stream As Stream = File.OpenRead(srcFileName)
      Dim imageInfoObject As Object = codecs.GetInformationAsync(stream, True, 1, Nothing)

      ' Notice that the returned imageInfoObject is a CodecsImageInfo with IsLoading set to true at this point
      ' The IsLoading will be false (and hence, the object will be usable) when the GetInformationAsyncCompleted
      ' fires.
   End Sub

   Private Sub GetInformationAsyncStreamExample_GetInformationAsyncCompleted(ByVal sender As Object, ByVal e As CodecsGetInformationAsyncCompletedEventArgs)
      If e.Cancelled Then
         Console.WriteLine("User canceled")
      ElseIf Not IsNothing(e.Error) Then
         Console.WriteLine("Error: " + e.Error.Message)
      Else
         ' Get the image info
         Dim info As CodecsImageInfo = DirectCast(e.Info, CodecsImageInfo)
         Console.WriteLine("Image info obtainted asynchronously:\n{0}", info.ToString())
         info.Dispose()
      End If

      ' We should close the stream here
      e.Stream.Dispose()

      ' Unsubscribe to the event and dispose the RasterCodecs object
      Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs)
      RemoveHandler codecs.GetInformationAsyncCompleted, AddressOf GetInformationAsyncStreamExample_GetInformationAsyncCompleted
      codecs.Dispose()
   End Sub

Public NotInheritable Class LEAD_VARS
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images"
End Class

public void GetInformationAsyncStreamExample()
     {
         string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp");

         RasterCodecs codecs = new RasterCodecs();

         // Now get information about the file asynchronously
         codecs.GetInformationAsyncCompleted += new EventHandler<CodecsGetInformationAsyncCompletedEventArgs>(GetInformationAsyncStreamExample_GetInformationAsyncCompleted);

         Stream stream = File.OpenRead(srcFileName);
         object imageInfoObject = codecs.GetInformationAsync(stream, true, 1, null);

         // Notice that the returned imageInfoObject is a CodecsImageInfo with IsLoading set to true at this point
         // The IsLoading will be false (and hence, the object will be usable) when the GetInformationAsyncCompleted
         // fires.
     }

     private void GetInformationAsyncStreamExample_GetInformationAsyncCompleted(object sender, CodecsGetInformationAsyncCompletedEventArgs e)
     {
         if (e.Cancelled)
         {
             Console.WriteLine("User canceled");
         }
         else if (e.Error != null)
         {
             Console.WriteLine("Error: " + e.Error.Message);
         }
         else
         {
             // Get the image info
             CodecsImageInfo info = e.Info;
             Console.WriteLine("Image info obtainted asynchronously:\n{0}", info.ToString());
             info.Dispose();
         }

         // We should close the stream here
         e.Stream.Dispose();

         // Unsubscribe to the event and dispose the RasterCodecs object
         RasterCodecs codecs = sender as RasterCodecs;
         codecs.GetInformationAsyncCompleted -= new EventHandler<CodecsGetInformationAsyncCompletedEventArgs>(GetInformationAsyncStreamExample_GetInformationAsyncCompleted);
         codecs.Dispose();
     }

static class LEAD_VARS
{
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images";
}

Requirements

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

RasterCodecs Class
RasterCodecs Members
Overload List
Loading and Saving Large Tiff Files
Speeding Up 1-Bit Documents