LoadAsync(Stream,LeadRect,Object) Method

Loads the specified rectangle from the specified image stream using default options asynchronously.

Syntax

public RasterImage LoadAsync( 
   Stream stream,
   LeadRect tile,
   object userState
)

public RasterImage LoadAsync( 
   Stream stream,
   LeadRect tile,
   object userState
)

 function Leadtools.Codecs.RasterCodecs.LoadAsync(Stream,LeadRect,Object)( 
   stream ,
   tile ,
   userState 
)

public:
RasterImage^ LoadAsync( 
   Stream^ stream,
   LeadRect tile,
   Object^ userState
)

'Declaration
 
Public Overloads Function LoadAsync( _
   ByVal stream As Stream, _
   ByVal tile As LeadRect, _
   ByVal userState As Object _
) As RasterImage

'Usage
 
Dim instance As RasterCodecs
Dim stream As Stream
Dim tile As LeadRect
Dim userState As Object
Dim value As RasterImage
 
value = instance.LoadAsync(stream, tile, userState)

Parameters

stream: A System.IO.Stream containing the image data to load.
tile: A Leadtools.LeadRect describing the tile/area of the image to load.
userState: A user-defined object that is passed to the method invoked when the asynchronous operation completes.

Return Value

The Leadtools.RasterImage object that this method loads. See remarks for the usage of this object.

Remarks

This method loads a section of an image stream (any format). The section begins is defined by tile rectangle.

LEADTOOLS will attempt to load corrupted files so you can see at least a portion of the image. For these images, the load methods succeed, but LoadStatus will return an error code.

Use the CodecsLoadOptions class to set up other load option parameters before calling this method.

Support for 12 and 16-bit grayscale images is only available in the Document/Medical Imaging editions.

For supported formats, refer to Summary of All Supported Image File Formats.

LEADTOOLS loads all PDF files as Raster PDF uncompressed RasterImageFormat.RasPdf, regardless of the compression and color space used when saving the file.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller thread will not be blocked and the method will return instantly with an instance of Leadtools.RasterImage that is in a loading status (RasterImage.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 loading the image, the various properties of the Leadtools.RasterImage will be populated with the image information and data and the RasterImage.IsLoading property will be set to false.

Do not poll the RasterImage.IsLoading property to determine whether the image has finished loading. Instead, subscribe to the LoadAsyncCompleted event to get notification when the LoadAsync(String,LeadRect,Int32,CodecsLoadByteOrder,Int32,Int32,Object) operation has completed and whether any errors occurred.

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

Example

Visual Basic
C#

Public Sub LoadAsyncStream3Example()
      Dim codecs As New RasterCodecs()

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

      ' Load a random tile from the image asynchronously
      Dim tileRect As New LeadRect(100, 50, 200, 150)
      AddHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncStream3Example_LoadAsyncCompleted
      Dim stream As Stream = File.OpenRead(srcFileName)
      Dim rasterImageObject As Object = codecs.LoadAsync(stream, tileRect, Nothing)

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

   Private Sub LoadAsyncStream3Example_LoadAsyncCompleted(ByVal sender As Object, ByVal e As CodecsLoadAsyncCompletedEventArgs)
      If e.Cancelled Then
         Console.WriteLine("User canceled")
      ElseIf Not IsNothing(e.Error) Then
         Console.WriteLine("Error: " + e.Error.Message)
      Else
         ' Everything is OK, get the image
         Dim image As RasterImage = e.Image
         Console.WriteLine("Image loaded OK, size: {0} by {1}, order: {2}, bits/pixel: {3}", image.Width, image.Height, image.Order, image.BitsPerPixel)
         image.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.LoadAsyncCompleted, AddressOf LoadAsyncStream3Example_LoadAsyncCompleted
      codecs.Dispose()
   End Sub

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

public void LoadAsyncStream3Example()
     {
         RasterCodecs codecs = new RasterCodecs();

         string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp");

         // Load a random tile from the image asynchronously
         LeadRect tileRect = new LeadRect(100, 50, 200, 150);
         codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncStream3Example_LoadAsyncCompleted);
         Stream stream = File.OpenRead(srcFileName);
         object rasterImageObject = codecs.LoadAsync(stream, tileRect, null);

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

     private void LoadAsyncStream3Example_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e)
     {
         if (e.Cancelled)
         {
             Console.WriteLine("User canceled");
         }
         else if (e.Error != null)
         {
             Console.WriteLine("Error: " + e.Error.Message);
         }
         else
         {
             // Everything is OK, get the image
             RasterImage image = e.Image;
             Console.WriteLine("Image loaded OK, size: {0} by {1}, order: {2}, bits/pixel: {3}", image.Width, image.Height, image.Order, image.BitsPerPixel);
             image.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.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncStream3Example_LoadAsyncCompleted);
         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 Images
Loading and Saving Large Tiff Files
Speeding Up 1-Bit Documents
Fast File Info