Issues updating an ObservableCollection from a background thread

Matt Norman 1

I am attempting to run my data collection process in a background thread and then update an ObservableCollection that is bound to a DataGrid.

I have tried most different solutions that I have found around the web and unfortunately all keep leading me back to an exception:

System.ArgumentException: 'Must create DependencySource on same Thread as the DependencyObject.'

I have created a test project that uses a new thread to get data and then updates the collection and it all works fine.

As soon as I do the same thing in my main project I just get the exception again.

The exception doesn't really point me to where the issue is so i'm not even sure i'm looking in the right place.

The method I am currently using is as follows:

Create simple lock object in view model: object agentRTDataLock = new object();
In constructor of view model, enable collection synchronization: BindingOperations.EnableCollectionSynchronization(RealTimeAgentData, agentRTDataLock);
In new thread, get new data and update collection: RealTimeAgentData = DataManagerRealTimeAgent.GetAgentData(selectedGroups);

I have also tried invoking the current dispatcher to update the collection but still get the same thing. I have also tried locking the object and that also gives me the same excpetion.

Does anyone have any ideas?

Viorel 114.7K Reputation points

2022-01-18T11:45:33.457+00:00

How did you use the dispatcher?

Which code (line) generates the exception?
Matt Norman 1 Reputation point

2022-01-18T11:49:57.13+00:00
This is one way I have tried to use the dispatcher:

App.Current.MainWindow.Dispatcher.BeginInvoke(new Action(() => { RealTimeAgentData = DataManagerRealTimeAgent.GetAgentData(AgentGroups.Where(a => a.IsChecked == true).Select(a => a.GroupName).ToList()); }));

The exception does not give a line of where it occurred which is why I am struggling with this. It will go through method fine but then throw straight after, likely when the control is updated based on the new collection.
Viorel 114.7K Reputation points

2022-01-18T12:08:06.06+00:00
Probably this usage of dispatcher reduces the parallelism. Maybe you can do something like this in your thread:

var new_data = get new data as a collection. . . App.Current.MainWindow.Dispatcher.BeginInvoke(new Action(() => { assign or move 'new_data' to 'RealTimeAgentData' }));

Also check if it works when you assign some simple sample data to RealTimeAgentData. (The values must be built inside the action).
Ken Tucker 5,851 Reputation points

2022-01-18T12:18:59.853+00:00
In the title to the question you are saying you are getting an exception updating an observable collection but it looks like you are using an generic list

RealTimeAgentData = DataManagerRealTimeAgent.GetAgentData(AgentGroups.Where(a => a.IsChecked == true).Select(a => a.GroupName).ToList());

Is there any other code that converts the list to an observable collection?
Matt Norman 1 Reputation point

2022-01-18T12:25:20.55+00:00

Can you clarify what you mean by 'The values must be built inside the action'? This would then run on the UI thread which would defeat the purpose.
Matt Norman 1 Reputation point

2022-01-18T12:50:04.323+00:00

Sorry I changed it to an ObservableCollection. I have changed back and forth to try different things.
Hui Liu-MSFT 47,341 Reputation points Microsoft Vendor

2022-01-24T06:11:17.473+00:00

Hi, @Matt Norman . Is there an update to this question? Could you show us the download link of your project or the complete code of your project for us to analyze and test?

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Issues updating an ObservableCollection from a background thread