UseAsync Method

C#
Visual Basic
WinRT C#
Java
Objective-C
WinRT JavaScript
C++

public void UseAsync()

'Declaration

Public Sub UseAsync()

'Usage

Dim instance As RasterCodecs
 
instance.UseAsync()

public void UseAsync()

 function Leadtools.Codecs.RasterCodecs.UseAsync()

public:
void UseAsync();

The RasterCodecs object supports getting information and loading image files asynchronously through the use of the GetInformationAsync, LoadAsync and LoadSvgAsyncmethods. These methods will use an internal WebClient object to perform their operations and this object will be created automatically on the first call to these methods and can be accessed through the AsyncWebClient property.

If it is desired to create the WebClient object manually (for example, to subscribe to any of its event or set the credentials prior to invoking any read operations), you can call UseAsync to create the object, change its behavior and then call GetInformationAsync, LoadAsync or LoadSvgAsync.

Note:UseAsync, AsyncWebClient, IsAsyncBusy, and CancelAsync are only applicable when the GetInformationAsync or LoadAsync was with the versions that take a Uri parameter. The versions that take a String or a Stream does not use a WebClient object internally. If you want to check the progress or cancel the operation then use the LoadImage event as normal.

This example will use UseAsync to create the WebClient object used by a RasterCodecs object for asynchronous operations. It will then change the cache policy of the web client object before loading an image asynchronously.

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

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Imports Leadtools
Imports Leadtools.Codecs
Imports Leadtools.ImageProcessing
Imports Leadtools.ImageProcessing.Color
Imports Leadtools.Drawing
Imports Leadtools.Svg

      
Public Sub UseAsyncExample()
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp")
   Dim uri As New Uri(srcFileName)
   Dim codecs As New RasterCodecs()

   ' The RasterCodecs.AsyncWebClient is Nothing first
   Debug.Assert(Not IsNothing(codecs.AsyncWebClient))

   ' Force the RasterCodecs object to create it
   codecs.UseAsync()

   ' Change the Cache policy
   codecs.AsyncWebClient.CachePolicy = New System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.CacheOnly)

   ' Now Load the file asynchronously
   AddHandler codecs.LoadAsyncCompleted, AddressOf useAsyncExample_LoadAsyncCompleted
   Dim image As RasterImage = codecs.LoadAsync(uri, Nothing)
End Sub

Private Sub useAsyncExample_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
      ' Get the image
      Dim image As RasterImage = e.Image
      Console.WriteLine("Image loaded asynchronously: Size = {0} by {1}", image.Width, image.Height)
      image.Dispose()
   End If

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

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

using Leadtools;
using Leadtools.Codecs;
using Leadtools.ImageProcessing;
using Leadtools.ImageProcessing.Color;
using Leadtools.Svg;

      
public void UseAsyncExample()
{
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp");
   Uri uri = new Uri(srcFileName);
   RasterCodecs codecs = new RasterCodecs();

   // The RasterCodecs.AsyncWebClient is null first
   Debug.Assert(codecs.AsyncWebClient == null);

   // Force the RasterCodecs object to create it
   codecs.UseAsync();

   // Change the Cache policy
   codecs.AsyncWebClient.CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.CacheOnly);

   // Now Load the file asynchronously
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(useAsyncExample_LoadAsyncCompleted);
   RasterImage image = codecs.LoadAsync(uri, null);
}

private void useAsyncExample_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e)
{
   if (e.Cancelled)
   {
      Console.WriteLine("User canceled");
   }
   else if (e.Error != null)
   {
      Console.WriteLine("Error: " + e.Error.Message);
   }
   else
   {
      // Get the image
      RasterImage image = e.Image;
      Console.WriteLine("Image loaded asynchronously: Size = {0} by {1}", image.Width, image.Height);
      image.Dispose();
   }

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

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

Target Platforms

Reference

RasterCodecs Class
RasterCodecs Members