Question

I designed a WPF application based on MVVM pattern and I need to get large amount of data from a webservice, and i do it with a BackgroundWorker inside the ViewModel. To modify the observable collection i have to use a dispatcher and the problem is here, even if i pass by reference UI Dispatcher it dosen’t work, it is like I use the inner dispatcher and my application get freezed until all data are retrived.

I try to get the UI Dispatcher in several ways, Dispatcher.CurrentDispatcher, Application.Dispatcher, App.Current.Dispatcher… doing some researches I read that it should be works, does someone have any suggestions?

Thank you
Marco

Update

Here some code: This is how I pass the Dispatcher to the ModelView

void AppWindow_Loaded(object sender, RoutedEventArgs e)
{
     this.DataContext = new ModelViewApplication(System.Windows.Threading.Dispatcher.CurrentDispatcher);
}

Then I try to get data in this way

public ModelViewApplication(Dispatcher _dispatcher)
{
    BackgroundWorker bw = new BackgroundWorker();
    bw.DoWork += new DoWorkEventHandler(getData);
    bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(completedData);

    bw.RunWorkerAsync();
}

public void getData(object sender, DoWorkEventArgs e)
{
    _dispatcher.Invoke(DispatcherPriority.Normal,
        new Action(
            delegate()
                 {
                 //Connect to webservice and retrieve data
                 ....
                 }));
}

It seems like the multithread dosen’t work

Answer 1

Use the BackgroundWorker to get your data, then use the RunWorkerCompleted to update the ObservableCollection. You shouldn’t need the Dispatcher at all

public ModelViewApplication()
{
    BackgroundWorker bw = new BackgroundWorker();
    bw.DoWork += new DoWorkEventHandler(getData);
    bw.RunWorkerCompleted += completedData;

    bw.RunWorkerAsync();
}

public void getData(object sender, DoWorkEventArgs e)
{
    //Connect to webservice and retrieve data
    e.Result = WebService.GetData();
}

private void completedData(object sender, RunWorkerCompletedEventArgs e)
{
    MyCollection = new ObservableCollection<SomeClass>((IList)e.Results);
}