Subscribe Method (RealtimeFeatureClass)

In This Topic

Subscribe to receive row events. This method must be called on the MCT. Use QueuedTask.Run.

Syntax

C#
Visual Basic (Declaration)

public RealtimeCursor Subscribe( 
   QueryFilter queryFilter,
   bool useRecyclingCursor
)

Public Function Subscribe( _
   ByVal queryFilter As QueryFilter, _
   ByVal useRecyclingCursor As Boolean _
) As RealtimeCursor

Parameters

queryFilter: A null query filter will cause all rows that become available to be retrieved.
useRecyclingCursor: If set to true, all the entries in RealtimeCursor will reference the most current row returned by RealtimeCursor.Current. To ensure all the entries in RealtimeCursor remain unique, set useRecyclingCursor to false. The default is true.

Return Value

A RealtimeCursor that encapsulates the retrieved rows, as well as provides facilities to wait for new row events.

Exceptions

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

Remarks

This method is thread-safe and it can be called on any thread. If the cursor is disposed or in the process of being disposed when this method is called it will result in undefined behavior. As opposed to SearchAndSubscribe, this method does not perform a Search operation. As a consequence, the returned RealtimeCursor will only iterate over rows that became available immediately after the execution of this method. If no query filter is set, all rows that become available will be retrieved.

Example

Subscribe to Streaming Data

//Note: with feature class we can also use a System Task to subscribe and
//process rows
await QueuedTask.Run(async () =>
{
  // or var rfc = realtimeDatastore.OpenTable(name) as RealtimeFeatureClass
  using (var rfc = streamLayer.GetFeatureClass())
  {
    //non-recycling cursor - 2nd param "false"
    //subscribe, pre-existing rows are not searched
    using (var rc = rfc.Subscribe(qfilter, false))
    {
      SpatialQueryFilter spatialFilter = new SpatialQueryFilter();
      //waiting for new features to be streamed
      //default is no cancellation
      while (await rc.WaitForRowsAsync())
      {
        while (rc.MoveNext())
        {
          using (var row = rc.Current)
          {
            switch (row.GetRowSource())
            {
              case RealtimeRowSource.EventInsert:
                //getting geometry from new events as they arrive
                Polygon poly = ((RealtimeFeature)row).GetShape() as Polygon;

                //using the geometry to select features from another feature layer
                spatialFilter.FilterGeometry = poly;//project poly if needed...
                countyFeatureLayer.Select(spatialFilter);
                continue;
              default:
                continue;
            }
          }                  
        }
      }
    }//row cursor is disposed. row cursor is unsubscribed
  }
});

Search Existing Data and Subscribe for Streaming Data

//Note we can use System Task with the Realtime feature class
//for subscribe
await System.Threading.Tasks.Task.Run(async () =>
// or use ... QueuedTask.Run()
{
  using (var rfc = streamLayer.GetFeatureClass())
  {
    //non-recycling cursor - 2nd param "false"
    using (var rc = rfc.SearchAndSubscribe(qfilter, false))
    {
      //waiting for new features to be streamed
      //default is no cancellation
      while (await rc.WaitForRowsAsync())
      {
        //pre-existing rows will be retrieved that were searched
        while (rc.MoveNext())
        {
          using (var row = rc.Current)
          {
            var row_source = row.GetRowSource();
            switch (row_source)
            {
              case RealtimeRowSource.EventDelete:
                //TODO - handle deletes
                break;
              case RealtimeRowSource.EventInsert:
                //TODO handle inserts
                break;
              case RealtimeRowSource.PreExisting:
                //TODO handle pre-existing rows
                break;
            }
          }
        }
      }
    }//row cursor is disposed. row cursor is unsubscribed
  }
});

Requirements

Target Platforms: Windows 11, Windows 10

ArcGIS Pro version: 3 or higher.

Reference

RealtimeFeatureClass Class
RealtimeFeatureClass Members

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