ViewModel and multithreading best practice

Question

I want to understand some best practices regarding using MVVM and multithreading. Let us assume I have a ViewModel and it has an observableCollection. Also, let us assume I pass this collection to another service class which does some calculation and then udpates my collection.

After a point I realize that I want to make this a multithreaded call. When I make the call to the service class using threads or tasks what results is a cross thread operation. The reason is quite obvious because the service class updates the collection whcih in turn will update the UI on the background thread.

In such scenarios what is the best practice? Should we always write our service class in such a way that it first clones the input and then updates that cloned copy? Or should the view model always assuem that the service calls might be multithreaded and send a cloned copy?

What would be the recommended way to solve this?

Thanks

Jithu

Answer 1

A solution that might solve the cross-thread exception is by implementing the OnPropertyChanged in the base class of all ViewModels to switch to the correct thread/synchronization context so all properties in the View that are bound to the changing property will have their handlers called on the correct thread. See: Avoid calling BeginInvoke() from ViewModel objects in multi-threaded c# MVVM application

If/when you create copies you are postponing the synchronization and, in many cases, making it harder than need be.

A web service will always return new objects, how you, or a framework, updates the model using these object is up to you. A lot would depend on the amount of checks and updates coming in. There is no recommended way, see whatever fits the applications requirements.