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LoadAsync(Uri,LeadRect,object) Method

Summary

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

Syntax
C#
VB
C++
public RasterImage LoadAsync( 
   Uri uri, 
   LeadRect tile, 
   object userState 
) 
Public Overloads Function LoadAsync( _ 
   ByVal uri As Uri, _ 
   ByVal tile As LeadRect, _ 
   ByVal userState As Object _ 
) As RasterImage 
public: 
RasterImage^ LoadAsync(  
   Uri^ uri, 
   LeadRect tile, 
   Object^ userState 
)  

Parameters

uri
The Uri containing the input image data.

tile
A 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 RasterImage object that this method loads. See remarks for the usage of this object.

Remarks

NOTE: This topic is part of RasterCodecs Async support using the .NET System.ComponentMode.AsyncOperation model. For .NET async/await support this type/member is not used. Instead, refer to RasterCodecs Async Operations.

This method loads a section of an image file (any format). The section beginning is defined by a 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 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.

LEADTOOLS supports the following URI schemes:

Scheme Description
UriSchemeFile Specifies that the URI is a disk file in local machine or universal naming convention (UNC) path.
UriSchemeHttp Specifies that the URI is accessed through the Hypertext Transfer Protocol (HTTP).
UriSchemeHttps Specifies that the URI is accessed through the Secure Hypertext Transfer Protocol (HTTPS).
UriSchemeFtp Specifies that the URI is accessed through the File Transfer Protocol (FTP).

If uri points to a resource in a UriSchemeHttp, UriSchemeHttps or UriSchemeFtp, then this RasterCodecs will attempt to download image data in an iterative fashion by creating a temporary buffer. The size of this buffer can be determined and changed by setting up the UriOperationBufferSize prior to calling this method.

For authenticity and proxy settings, refer to UriOperationCredentials and UriOperationProxy.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller's thread will not be blocked and the method will return instantly with an instance of 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 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 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.

The CodecsLoadOptions.AllPages property controls whether RasterCodecs will try to load all pages or just the first page if the image data contains multiple pages.

Example
C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void LoadAsyncUrl2Example() 
{ 
   RasterCodecs codecs = new RasterCodecs(); 
 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
   Uri uri = new Uri(srcFileName); 
 
   // Load a random tile from the image asynchronously 
   LeadRect tileRect = new LeadRect(100, 50, 200, 150); 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncUrl2Example_LoadAsyncCompleted); 
   object rasterImageObject = codecs.LoadAsync(uri, 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 LoadAsyncUrl2Example_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 at {0} loaded OK, size: {1} by {2}, order: {3}, bits/pixel: {4}", e.Uri, image.Width, image.Height, image.Order, image.BitsPerPixel); 
      image.Dispose(); 
   } 
 
   // Unsubscribe to the event and dispose the RasterCodecs object 
   RasterCodecs codecs = sender as RasterCodecs; 
   codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncUrl2Example_LoadAsyncCompleted); 
   codecs.Dispose(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; 
} 
Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.ImageProcessing 
Imports Leadtools.ImageProcessing.Color 
Imports Leadtools.Drawing 
Imports Leadtools.Svg 
 
Public Sub LoadAsyncUrl2Example() 
   Dim codecs As New RasterCodecs() 
 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp") 
   Dim uri As New Uri(srcFileName) 
 
   ' Load a random tile from the image asynchronously 
   Dim tileRect As New LeadRect(100, 50, 200, 150) 
   AddHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncUrl2Example_LoadAsyncCompleted 
   Dim rasterImageObject As Object = codecs.LoadAsync(uri, 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 LoadAsyncUrl2Example_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 at {0} loaded OK, size: {1} by {2}, order: {3}, bits/pixel: {4}", e.Uri, image.Width, image.Height, image.Order, image.BitsPerPixel) 
      image.Dispose() 
   End If 
 
   ' Unsubscribe to the event and dispose the RasterCodecs object 
   Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs) 
   RemoveHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncUrl2Example_LoadAsyncCompleted 
   codecs.Dispose() 
End Sub 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class 
Requirements

Target Platforms

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Leadtools.Codecs Assembly