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LoadAsyncCompleted Event

Summary

Indicates that an asynchronous load operation has been completed.

Syntax
C#
VB
Java
C++
public event EventHandler<CodecsLoadAsyncCompletedEventArgs> LoadAsyncCompleted 
Public Event LoadAsyncCompleted As EventHandler(Of CodecsLoadAsyncCompletedEventArgs) 
synchronized public void addLoadAsyncCompletedListener(CodecsLoadAsyncCompletedListener listener) 
synchronized public void removeLoadAsyncCompletedListener(CodecsLoadAsyncCompletedListener listener) 
public: 
event EventHandler<CodecsLoadAsyncCompletedEventArgs^>^ LoadAsyncCompleted 

Event Data

The event handler receives an argument of type CodecsLoadAsyncCompletedEventArgs containing data related to this event. The following CodecsLoadAsyncCompletedEventArgs properties provide information specific to this event.

PropertyDescription
Cancelled (Inherited from System.ComponentModel.AsyncCompletedEventArgs)Gets a value indicating whether an asynchronous operation has been canceled.
Error (Inherited from System.ComponentModel.AsyncCompletedEventArgs)Gets a value indicating which error occurred during an asynchronous operation.
FileName (Inherited from Leadtools.Codecs.CodecsAsyncCompletedEventArgs)Gets the file name this asynchronous operation is using.
Image Gets the RasterImage class instance that is being loaded.
Stream (Inherited from Leadtools.Codecs.CodecsAsyncCompletedEventArgs)Gets the stream this asynchronous operation is using.
Uri (Inherited from Leadtools.Codecs.CodecsAsyncCompletedEventArgs)Gets the URI this asynchronous operation is using.
UserState (Inherited from System.ComponentModel.AsyncCompletedEventArgs)Gets the unique identifier for the asynchronous task.

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.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller 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.

It is recommended that you do not poll for the RasterImage.IsLoading property to determine whether the image is finished loaded, instead, subscribe to the LoadAsyncCompleted event to get notification on when the LoadAsync operation is 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 LoadAsyncCompleted event uses a data argument object of type CodecsLoadAsyncCompletedEventArgs. This class contains the following properties:

Property Description
CodecsLoadAsyncCompletedEventArgs.Uri, CodecsLoadAsyncCompletedEventArgs.Stream and CodecsLoadAsyncCompletedEventArgs.FileName

Contains the URI, stream or file name passed to the method that initialized this asynchronous operation.

Only one of these properties can be a valid value (not a null reference) at any time The property that contains a valid reference depends on what version of LoadAsync method has been called.

For example, if LoadAsync(Uri uri, object userState) is being called, the Uri will contain the same URI passed to the method while Stream and FileName will both be null. If LoadAsync(String fileName, object userState) is being called, the FileName will contain the same file name string value passed to the method while Uri and Stream will both be null and so on.

CodecsLoadAsyncCompletedEventArgs.Image

Contains the RasterImage class instance that contains the image data being loaded. This instance is the same object returned from the LoadAsync method. While the asynchronous operation is running, the value of the RasterImage.IsLoading will be true indicating that the object is being populated with the image information and should not be used. When the asynchronous operation completes, the LoadAsyncCompleted event will fire and Image will contain the final and ready to use object. If an error occurs, this property will be set to null and the object is disposed internally by the toolkit.

CodecsLoadAsyncCompletedEventArgs.Error

Contains any errors that might have occurred during the asynchronous operation. You must check this value when the LoadAsyncCompleted event fires and make sure it does not contain a valid Exception object.

CodecsLoadAsyncCompletedEventArgs.Cancelled

Contains a value indicating whether an asynchronous operation has been canceled. For example, by calling CancelAsync when using RasterCodecs.LoadAsync with a URL.

Example
C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void LoadAsyncCompletedExample() 
{ 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
   Uri uri = new Uri(srcFileName); 
 
   RasterCodecs codecs = new RasterCodecs(); 
 
   // Now load the image asynchronously 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncCompletedExample_LoadAsyncCompleted); 
   object rasterImageObject = codecs.LoadAsync(uri, 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 LoadAsyncCompletedExample_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}", e.Uri, 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>(LoadAsyncCompletedExample_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 LoadAsyncCompletedExample() 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp") 
   Dim uri As New Uri(srcFileName) 
 
   Dim codecs As New RasterCodecs() 
 
   ' Now load the image asynchronously 
   AddHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncCompletedExample_LoadAsyncCompleted 
   Dim rasterImageObject As Object = codecs.LoadAsync(uri, 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 LoadAsyncCompletedExample_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}", e.Uri, 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 LoadAsyncCompletedExample_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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