WaitForRowsAsync(CancellationToken) Method

In This Topic

Asynchronously waits for new rows to be available in the internal queue of this real-time cursor. The returned System.Threading.Tasks.Task will also complete if the state of this RealtimeCursor (see GetState) changes from RealtimeCursorState.Subscribed. This method can be called on any thread.

Syntax

C#
Visual Basic (Declaration)

public Task<bool> WaitForRowsAsync( 
   CancellationToken cancellationToken
)

Public Overloads Function WaitForRowsAsync( _
   ByVal cancellationToken As CancellationToken _
) As Task(Of Boolean)

Parameters

cancellationToken: A System.Threading.CancellationToken used to control cancellation behavior for the returned task.

Return Value

A System.Threading.Tasks.Task that will complete once this cursor becomes unsubscribed or new rows are available in the internal queue of this real-time cursor. The returned System.Boolean value is false if this cursor is unsubscribed and there are no more rows to be read. Otherwise it's true.

Exceptions

Exception	Description
ArcGIS.Core.Data.Exceptions.GeodatabaseException	A geodatabase-related exception has occurred.

Example

Explicitly Cancel WaitForRowsAsync

//somewhere in our code we create a CancellationTokenSource
var cancel = new CancellationTokenSource();
//...

//call cancel on the CancellationTokenSource anywhere in
//the add-in, assuming the CancellationTokenSource is in scope
if (SomeConditionForCancel)
  cancel.Cancel();//<-- will cancel the token

//Within QueuedTask we are subscribed! streamLayer.Subscribe() or SearchAndSubscribe()
try
{
  //TaskCanceledException will be thrown when the token is cancelled
  while (await rc.WaitForRowsAsync(cancel.Token))
  {
    //check for row events
    while (rc.MoveNext())
    {
      using (var row = rc.Current)
      {
        //etc
      }
    }
  }
}
catch (TaskCanceledException tce)
{
  //Handle cancellation as needed
}
cancel.Dispose();

Search And Subscribe With Cancellation

await QueuedTask.Run(async () =>
{
  //Recycling cursor - 2nd param "true"
  //or streamLayer.Subscribe(qfilter, true) to just subscribe
  using (var rc = streamLayer.SearchAndSubscribe(qfilter, true))
  {
    //auto-cancel after 20 seconds
    var cancel = new CancellationTokenSource(new TimeSpan(0, 0, 20));
    //catch TaskCanceledException
    try
    {
      while (await rc.WaitForRowsAsync(cancel.Token))
      {
        //check for row events
        while (rc.MoveNext())
        {
          using (var row = rc.Current)
          {
            //etc
          }
        }
      }
    }
    catch (TaskCanceledException tce)
    {
      //Handle cancellation as needed
    }
    cancel.Dispose();
  }
});

Requirements

Target Platforms: Windows 11, Windows 10, Windows 8.1

Reference

RealtimeCursor Class
RealtimeCursor Members
Overload List
GetState Method

Send feedback