SynchronizationContext.Current is null on resolving with Unity in WPF

Question

I have a WPF Code which looks something like this.

public class AlphaProductesVM : BaseModel
{
    private  ObservableCollection

        

Answer 1

I'm not sure if this will be a popular suggestion, but you could lazily create and subscribe to your collection. Then the first access to NwCustomers from the UI thread will kick everything off correctly.

public AlphaProductesVM (){}

public ObservableCollection<Alphabetical_list_of_product> NwCustomers
{
    get { 
          if(_NwCustomers == null)
          {
              _NwCustomers = new ObservableCollection<Alphabetical_list_of_product>();
              var repository = new NorthwindRepository();
                  repository
                  .GetAllProducts()
                  .ObserveOn(SynchronizationContext.Current)
                  .Subscribe(AddElement);
          }
          return _NwCustomers; 
    }
}

or, if you inject the UI thread's dispatcher into your view model you can subscribe on that in the constructor.

              var repository = new NorthwindRepository();
                  repository
                  .GetAllProducts()
                  .ObserveOn(theUIdispatcher)
                  .Subscribe(AddElement);

Answer 2

The SynchronizationContext.Current property will only return a value when invoked on the main thread.

If you need to use a SynchronizationContext object in threads other than the main thread, you could pass the SynchronizationContext instance associated to the main thread to the classes that need it as a dependency.

If you choose this solution, you could register the SynchronizationContext object obtained from the SynchronizationContext.Current property on the main thread as a singleton in your container. That way all requests for a SynchronizationContext from that point on will automatically be satisfied by the container with the singleton:

// Must run in the main thread
container.RegisterInstance(SynchronizationContext.Current);

Answer 3

Although there is an implementation of SynchronizationContextfor WPF it is not recommended for use. WPF has the Dispatcher to build responsive applications.

In addition SynchronizationContext.Current only has a value if you are on the UI thread. If your logic runs in a background thread Current will always be null.