Synchronous method for QueryTask?

Question

QueryTask has an ExecuteAsync() method, but I need a synchronous version.  I have to pull in all the features of a layer before proceeding further with the program.

How can I achieve this?

MikeDuppong · Answer

Thank you, Surgey - I was actually working on a very similar solution, but I'm taking some pointers with your example.

I appreciate your time and help.

Mike

SanajyJadhav · Answer

I am not sure but can't you use FeatureLayer with mode "Selection"?

SergeyZorin · Answer

You can "emulate" synchronous call using ManualResetEvent. Here is code from my project (modified it a bit to remove project-specific code). It works for spatial query but you can always modify it to use "where" clause. public FeatureSet Query(Geometry geometry, string layerURL) { if (Dispatcher.CheckAccess()) { var message = string.Format("\"Query\" method should be called on background thread."); throw new Exception(message); } FeatureSet result = null; Exception error = null; var manualResetEvent = new ManualResetEvent(false); Dispatcher.Invoke(() => { var queryTask = new QueryTask(layerURL); var query = new Query(); query.OutFields.Add("*"); query.Geometry = geometry; query.ReturnGeometry = true; query.OutSpatialReference = Map.SpatialReference; EventHandler onTaskFailed = null; EventHandler onExecuteCompleted = null; onTaskFailed = (s, a) => { queryTask.ExecuteCompleted -= onExecuteCompleted; queryTask.Failed -= onTaskFailed; error = a.Error; manualResetEvent.Set(); }; onExecuteCompleted = (s, a) => { queryTask.ExecuteCompleted -= onExecuteCompleted; queryTask.Failed -= onTaskFailed; result = a.FeatureSet; manualResetEvent.Set(); }; queryTask.ExecuteCompleted += onExecuteCompleted; queryTask.Failed += onTaskFailed; queryTask.ExecuteAsync(query); }); manualResetEvent.WaitOne(); if (error == null) { return result; } else { throw error; } } You can get Dispatcher instance from any UI control, for example layout root. Also you must call this method on background thread (exception on the first line is for a purpose) because manual reset event will block UI thread and entire application. You can do this by using BackgroundWorker: backgroundWorker.DoWork += (s, a) => { [your code here] var featureSet = Query(geometry, layerURL); [your code here using featureSet] var maybeAnotherFeatureSet = Query(geometry2, layerURL2); [you code here using both feature sets] }; backgroundWorker.RunWorkerCompleted += (s, a) => { [output results and throw errors here] }; backgroundWorker.RunWorkerAsync(); Using this approach you can group and chain asynchronous calls into one asynchronous background worker call. P.S. so much code/text here, now I think it can be overkill for your problem.