UseAsync Method

Visual Basic
C#
WinRT 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(String,Boolean,Int32,Object) and LoadAsync(String,LeadRect,Int32,CodecsLoadByteOrder,Int32,Int32,Object) methods. These methods will use an internal System.Net.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 System.Net.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(String,Boolean,Int32,Object) or LoadAsync(String,LeadRect,Int32,CodecsLoadByteOrder,Int32,Int32,Object).

Note:UseAsync, AsyncWebClient, IsAsyncBusy, and CancelAsync are only applicable when the GetInformationAsync(String,Boolean,Int32,Object) or LoadAsync(String,LeadRect,Int32,CodecsLoadByteOrder,Int32,Int32,Object) was with the versions that take a System.Uri parameter. The versions that take a System.String or a System.IO.Stream does not use a System.Net.WebClient object internally. If you want to check the progress or cancel the operation then use the LoadImage event as normal.

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

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

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: 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