CancelAsync Method

Summary

Cancels a pending asynchronous operation.

Syntax

C++/CLI

Java

Python

public void CancelAsync()

public void cancelAsync(Object operation)

public: 
void CancelAsync();

def CancelAsync(self):

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 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 take 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.

Example

Java

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
 
 
public void CancelAsyncExample() 
{ 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
   Uri uri = new Uri(srcFileName); 
 
   RasterCodecs codecs = new RasterCodecs(); 
 
   // Now Load the file asynchronously 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(cancelAsyncExample_LoadAsyncCompleted); 
   RasterImage image = codecs.LoadAsync(uri, null); 
 
   // Cancel it immediatly, in normal situation, the cancelation will happen 
   // before the LoadAsync method has a chance to load the file and 
   // the message "User canceled" will be displayed on the console 
   if (codecs.IsAsyncBusy) 
   { 
      codecs.CancelAsync(); 
   } 
} 
 
private void cancelAsyncExample_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e) 
{ 
   if (e.Cancelled) 
   { 
      Debug.WriteLine("User canceled"); 
   } 
   else if (e.Error != null) 
   { 
      Debug.WriteLine("Error: " + e.Error.Message); 
   } 
   else 
   { 
      // Get the image 
      RasterImage image = e.Image; 
      Debug.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>(cancelAsyncExample_LoadAsyncCompleted); 
   codecs.Dispose(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS23\Resources\Images"; 
}

 
import java.io.*; 
import java.net.*; 
import java.nio.file.Paths; 
import java.util.*; 
import java.time.Instant; 
import java.time.Duration; 
 
import org.junit.*; 
import org.junit.runner.JUnitCore; 
import org.junit.runner.Result; 
import org.junit.runner.notification.Failure; 
import static org.junit.Assert.*; 
 
import leadtools.*; 
import leadtools.codecs.*; 
import leadtools.codecs.RasterCodecs.FeedCallbackThunk; 
import leadtools.drawing.internal.*; 
import leadtools.imageprocessing.*; 
import leadtools.imageprocessing.color.ChangeIntensityCommand; 
import leadtools.svg.*; 
 
 
public void cancelAsyncExample() throws URISyntaxException, IOException { 
   final String LEAD_VARS_IMAGES_DIR = "C:\\LEADTOOLS23\\Resources\\Images"; 
   String srcFileName = combine(LEAD_VARS_IMAGES_DIR, "Image1.cmp"); 
   URI uri = Paths.get(srcFileName).toUri(); 
   RasterCodecs codecs = new RasterCodecs(); 
 
   // Now Load the file asynchronously 
   codecs.addLoadAsyncCompletedListener(cancelAsyncExampleLoadAsyncCompleted); 
   ILeadStream uriStream = LeadStreamFactory.create(uri); 
   Object operation = codecs.loadAsync(uriStream, null); 
 
   // Cancel it immediatly, in normal situation, the cancelation will happen 
   // before the LoadAsync method has a chance to load the file and 
   // the message "User canceled" will be displayed on the console 
   if (codecs.isAsyncBusy(operation)) { 
      codecs.cancelAsync(operation); 
   } 
   assertTrue("Check that URI exists", uri != null); 
   System.out.println("The URI exists"); 
   uriStream.close(); 
} 
 
CodecsLoadAsyncCompletedListener cancelAsyncExampleLoadAsyncCompleted = new CodecsLoadAsyncCompletedListener() { 
 
   @Override 
   public void onLoadAsyncCompleted(CodecsLoadAsyncCompletedEvent e) { 
      if (e.getCancelled()) { 
         System.out.println("User canceled"); 
      } else if (e.getError() != null) { 
         System.out.println("Error: " + e.getError().getMessage()); 
      } else { 
         // Get the image 
         RasterImage image = e.getImage(); 
         System.out.printf("Image loaded asynchronously: Size = %s by %s%n", image.getWidth(), image.getHeight()); 
         image.dispose(); 
      } 
 
      // Unsubscribe to the event and dispose the RasterCodecs object 
      RasterCodecs codecs = (RasterCodecs) e.getSource(); 
      codecs.removeLoadAsyncCompletedListener(cancelAsyncExampleLoadAsyncCompleted); 
      codecs.dispose(); 
   } 
 
};

Requirements

Target Platforms

Reference

RasterCodecs Class

RasterCodecs Members

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