INotifyPropertyChanged Binding and Cross-Threading Error

Question

I have a GridView element on my GUI that is bound to a data source. I decided to use the INotifyPropertyChanged as that would simplify the interaction by allowing me to modify a class which would automatically update the GridView. Up to this point I have not had any problems with cross-threading, but now I added another method that modifies my class (which in turn modifies the GridView), but this is taking place on a non-UI thread. I have solved my problems before by using an invoke , but I am not sure how do to it when I am implementing the INotifyPropertyChanged and binding it to the GridView . Any help would be very much appreciated!

Answer 1

Let's say you have an observable collection that is tied to your grid. The grid is the View.

When a callout is made to retrieve data, the callout will be async to return data. On the Async event handler, you would want something like this in your View Model class:

    /// <summary>
    /// This is what is bound to the UI
    /// </summary>
    private ObservableCollection<UserDTO> _Users;

    /// <summary>
    /// Collection of Users
    /// </summary>
    public ObservableCollection<UserDTO> Users
    {
        get
        {
            return _Users;
        }
        set
        {
            if (_Users != value)
            {
                _Users = value;
                OnPropertyChanged("Users");
            }
        }
    }

    /// <summary>
    /// Asynchronous Callback For Get Users
    /// </summary>
    private void UserAgentGetCompleted(object sender, List<UserDto> users)
    {

         //Make sure we are on the UI thread
          this.Dispatcher.BeginInvoke(() => SetUsers(users));

    }

Then in SetUsers you would update the observable collection (_Users) that is data bound to the view (grid). Since the observable collection updates, the changes will be reflected in the view since it is bound to the view via a dependency property.

Note, I've omitted the SetUsers() code, but all that is doing is setting the incoming user list to the observable collection.