Creates the WebClient object used for asynchronous operations.
public void UseAsync()
Public Sub UseAsync()
public:
void UseAsync();
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.
The RasterCodecs object supports getting information, loading and saving image files asynchronously through the use of the GetInformationAsync, LoadAsync, LoadSvgAsync and SaveAsync methods. 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, LoadSvgAsync or SaveAsync.
Note: UseAsync, AsyncWebClient, IsAsyncBusy, and CancelAsync are only applicable when the GetInformationAsync, LoadAsync, LoadSvgAsync or SaveAsync was with the versions that takes a Uri parameter. The versions that take a String or a Stream do 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.
using Leadtools;
using Leadtools.Codecs;
using Leadtools.ImageProcessing;
using Leadtools.ImageProcessing.Color;
using Leadtools.Svg;
using LeadtoolsExamples.Common;
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";
}
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
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