ArcGIS Pro 3.0 API Reference Guide
ArcGIS.Core.Data.Realtime Namespace / RealtimeCursor Class / MoveNext Method
Example

In This Topic
    MoveNext Method (RealtimeCursor)
    In This Topic
    Advances to the next RealtimeRow in this RealtimeCursor. This method can be called on any thread.
    Syntax
    public bool MoveNext()
    Public Function MoveNext() As Boolean

    Return Value

    true if the cursor has successfully advanced to the next row; false if the cursor has passed the end of the collection.
    Exceptions
    ExceptionDescription
    A geodatabase-related exception has occurred.
    Remarks
    The RealtimeCursor can only advance sequentially forward. To move the cursor back to the beginning, you will have to reexecute the search to obtain a new row cursor.
    Example
    Search And Subscribe for Streaming Data
    await QueuedTask.Run(async () =>
    {
      //query filter can be null to search and retrieve all rows
      //true means recycling cursor
      using (var rc = streamLayer.SearchAndSubscribe(qfilter, true))
      {
        //waiting for new features to be streamed
        //default is no cancellation
        while (await rc.WaitForRowsAsync())
        {
          while (rc.MoveNext())
          {
            using (var row = rc.Current)
            {
              //determine the origin of the row event
              switch (row.GetRowSource())
              {
                case RealtimeRowSource.PreExisting:
                  //pre-existing row at the time of subscribe
                  continue;
                case RealtimeRowSource.EventInsert:
                  //row was inserted after subscribe
                  continue;
                case RealtimeRowSource.EventDelete:
                  //row was deleted after subscribe
                  continue;
              }
            }
          }
        }
      }//row cursor is disposed. row cursor is unsubscribed
    
      //....or....
      //Use the feature class instead of the layer
      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())
          {
            //etc
          }
        }
      }
    });
    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();
      }
    });
    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();
    
    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
      }
    });
    
    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

    See Also