Leadtools.Codecs Namespace > RasterCodecs Class : UseAsync Method |
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.
Imports Leadtools Imports Leadtools.Codecs Imports Leadtools.ImageProcessing Imports Leadtools.ImageProcessing.Color Imports Leadtools.Drawing 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; 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"; }