WaitForRowsAsync() Method
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.
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.
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();
}
});
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
}
});
Target Platforms: Windows 11, Windows 10, Windows 8.1