Question

iv’e got an mvvm application ,

in a viewmodel :

    public CommandViewModel()         
    {
        Messenger.Default.Register<CustomerSavedMessage>(this, message =>
        {
            Customers.Add(message.UpdatedCustomer);
        });
    } 

    private ObservableCollection<Customer> _customers;
    public ObservableCollection<Customer> Customers 
    {
        get { return _customers; }
        set
        {
            _customers = value;
            OnPropertyChanged("Customers");
        }
    }

Customers is bound to a combobox in my view .

in a different viewmodel i raise a CustomerSavedMessage on a different thread
when i attempt to handle the message in the Register’s handler delegate above
a notsupportedexception is thrown with the following message :

   {"This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread."}

i obviously need to use the Dispatcher object for the cross thread operation,
but i can’t figure out how this is done from the viewmodel .

also i thought that the framework would know how to handle cross threading between over binding ..

how can i execute the Customers.Add(message.UpdatedCustomer) on the Dispatcher thread ?

Answer 1

You can use Application.Current.Dispatcher to get Dispatcher for application’s main thread or capture dispatcher in your ViewModel constructor (Dispatcher.CurrentDispatcher).

For example:

Messenger.Default.Register<CustomerSavedMessage>(this, message =>
{
     Application.Current.Dispatcher.Invoke(
         new Action(() => Customers.Add(message.UpdatedCustomer))); 
});