topic Graphics Layer inaccessible by background thread in ArcGIS Runtime SDK for WPF (Retired) Questions

Graphics Layer inaccessible by background thread

DipinBehl — Mon, 16 Jan 2012 10:17:06 GMT

Hi All,

I am using ArcGis API for WPF in a desktop based application to show locations, route for the stops on a 2D Map.
A background thread fetches the locations (along with lat-long) from a WCF service. Then these locations are displayed on the Map as TextSymbol(s) on a GraphicLayer.
Then another background thread calls a WCF RESTfull resource to find route for the locations (stops). This call returns me a route which i am trying to display on the map using another GraphicLayer using 'Add' method of the 'Graphics' property of the layer. Whenever i try to do so, i get an exception 'The calling thread cannot access this object because a different thread owns it.'
I have tried to use Dispatcher object for the screen, the map object, the graphics layer but none seems to work for me.

Re: Graphics Layer inaccessible by background thread

LorenCress — Thu, 02 Feb 2012 19:13:38 GMT

I have tried to use Dispatcher object for the screen, the map object, the graphics layer but none seems to work for me.

Can you post the code that you are using to accomplish this? What error do you get when you attempt to use the Dispatcher?

Re: Graphics Layer inaccessible by background thread

ApurvaGoyal — Fri, 04 May 2012 16:52:29 GMT

Can you post the code that you are using to accomplish this? What error do you get when you attempt to use the Dispatcher?

I am getting similar error on my WPF application. Here is the code I am using-

BackgroundWorker worker = new BackgroundWorker();
                        worker.WorkerSupportsCancellation = true;
                        //this is where the long running process should go
                        worker.DoWork += (o, ea) =>
                        {
                            ea.Result = ReadShapeFileAsGraphics(droppedFilePaths[0]);
                        };
                        worker.RunWorkerCompleted += (o, ea) =>
                        {
                            IEnumerable<Graphic> graphics = ea.Result as IEnumerable<Graphic>;
                            Dispatcher.CurrentDispatcher.Invoke((System.Action)(() =>
                                {
                                    if (graphics.Count() > 0)
                                        foreach (Graphic g in graphics)
                                            GraphicLayer.GraphicsSource = graphics;

                                }));

                            //work has completed. you can now interact with the UI
                            IsBusy = false;
                        };
                        //set the IsBusy before you start the thread
                        IsBusy = true;
                        worker.RunWorkerAsync();

Thanks

Apurva

Re: Graphics Layer inaccessible by background thread

LorenCress — Sun, 12 Dec 2021 04:15:11 GMT

There are two issues here:

                                    if (graphics.Count() > 0)
                                        foreach (Graphic g in graphics)
                                            GraphicLayer.GraphicsSource = graphics;

This should be:

                                    if (graphics.Count() > 0)
                                        GraphicLayer.GraphicsSource = graphics;

Secondly, and more importantly:

                            Dispatcher.CurrentDispatcher.Invoke((System.Action)(() =>

...should be:

                            Dispatcher.CurrentDispatcher.Invoke((System.Action)((graphics) =>

Re: Graphics Layer inaccessible by background thread

BrianLocke — Tue, 09 Jul 2013 06:47:02 GMT

Isn't the System.Action Anonymous and takes 0 args?

would we have to create a new delegate with a Graphic set as one of the args....

??? I have been trying to get this to work for days now and still can't seem to get this thing going 😞

Re: Graphics Layer inaccessible by background thread

LorenCress — Wed, 10 Jul 2013 00:49:53 GMT

Isn't the System.Action Anonymous and takes 0 args?

would we have to create a new delegate with a Graphic set as one of the args....

??? I have been trying to get this to work for days now and still can't seem to get this thing going 😞

System.Action is anonymous in this example, but it can take an argument (or more than one, if needed; see the link), so it doesn't need to have a delegate.

Re: Graphics Layer inaccessible by background thread

MichaelBranscomb — Wed, 10 Jul 2013 07:37:12 GMT

Hi,

I haven't had a chance to read the whole thread here - but you might want to take a look at the synchronization context info in http://forums.arcgis.com/threads/60409-Is-it-possible-to-edit-file-gdb-feature-classes-from-Windows-Service.

Cheers

Mike