topic Re: Using Geometry service using TPL in ArcGIS API for Silverlight Questions

Using Geometry service using TPL

George_J_Capnias — Sun, 12 Dec 2021 04:24:19 GMT

Hi,
I am trying to implement a sequence of calls to Geometry service. I want to implements these calls as Tasks.
I have the following extension method,

public static Task<IList<Graphic>> SimplifyTask(this GeometryService gc, IList<Graphic> graphics)
{
 TaskCompletionSource<IList<Graphic>> tcs = new TaskCompletionSource<IList<Graphic>>();
 EventHandler<GraphicsEventArgs> SimplifyCompleted = delegate { };
 EventHandler<TaskFailedEventArgs> Failed = delegate { };
 SimplifyCompleted = (sender, e) =>
 {
  gc.SimplifyCompleted -= SimplifyCompleted;
  gc.Failed -= Failed;
  tcs.TrySetResult(e.Results);
 };
 Failed = (sender, e) =>
 {
  gc.SimplifyCompleted -= SimplifyCompleted;
  gc.Failed -= Failed;
  tcs.TrySetException(e.Error);
 };
 try
 {
  gc.SimplifyCompleted += SimplifyCompleted;
  gc.Failed += Failed;
  gc.SimplifyAsync(graphics);
 }
 catch (Exception ex)
 {
  tcs.TrySetException(ex);
  gc.SimplifyCompleted -= SimplifyCompleted;
  gc.Failed -= Failed;
 }
 return tcs.Task;
}

that I am trying to use through this code:

 geometryService = new GeometryService("http://arcgis/ArcGIS/rest/services/Geometry/GeometryServer");
 Task<IList<Graphic>> task1 = geometryService.SimplifyTask(PstLayer.Graphics);
 Task.WaitAll(task1);
 IList<Graphic> simplifiedPstLayer = task1.Result;

When the code reaches "Task.WaitAll(task1);" line, I wait for ever; Having breakpoints inside SimplifyCompleted and Failed handlers, the execution never reaches this point...
Is there any help, pointers somebody has to offer?

Thanks,
George J.

Re: Using Geometry service using TPL

DominiqueBroux — Sun, 12 Dec 2021 04:24:22 GMT

 Task.WaitAll(task1);
When the code reaches "Task.WaitAll(task1);" line, I wait for ever;

Your call to WaitAll is blocking the UIThread and as SimplifyAsync is an asynchronous method which needs the UIThread, you are stuck.

It's exactly what the new C# 'await' operator is done for : i.e. to use asynchonous task without blocking the thread.

That being said, .Net Framework 4.0 and SL5 doesn't support the 'await' operator except if you download and install the Async Targetting Pack

Without this pack, you can get the same behavior by using the ContinueWith method.

Something like:

Task<IList<Graphic>> task1 = geometryService.SimplifyTask(PstLayer.Graphics);
task1.ContinueWith(t =>
{
    IList<Graphic> simplifiedPstLayer = t.Result;

    // add here your code using the simplified graphics

}, TaskScheduler.FromCurrentSynchronizationContext()); 


// No more code here

Obviously the syntaxic sugar of the await operator gets lost.

Note : another option would be to execute your task in another thread, but in this particular case it's not working since the graphics need to be created in the UIThread and so SymplifyAsync can only be executed in the UI Thread.

Re: Using Geometry service using TPL

DenisT — Fri, 06 Sep 2013 15:42:57 GMT

Better late than never.

There is an extension for SL API that can help you with async/await:
https://arcgisasync.codeplex.com/