Problems refreshing a Silverlight DataGrid

I am having a problem using a Silverlight data grid with an observeable collection. I have crated a Silverlight data grid, filled an observerable collection from WCF R开发者_JAVA技巧IA services and bound a collection to the grid. It works fine for the first time, but when I change the item source contents, the data is not refreshed in the grid. When I double-click on the datagrid cells, the contents are displayed. I may be missing some basic property settings. Can any one help?

Sample Code :

 App.BPIContext.Load(App.BPIContext.GetWellFieldListValuesQuery()).Completed += DataSource_WellFieldDataListValueLoadComplete;


ObservableCollection<ScheduleWellCustomFields> _userWellCustomFields = new ObservableCollection<ScheduleWellCustomFields>();

    void DataSource_WellCustomFieldsLoadComplete(object sender, EventArgs e)
    {
        _userWellCustomFields.Clear();
        App.BPIContext.ScheduleWellCustomFields.ToList().ForEach(c => _userWellCustomFields.Add(c));
        this.dtGridDrillingEngineer.ItemsSource = _userWellCustomFields;
    }

Try to add this.dtGridDrillingEngineer.ItemsSource = null; before his.dtGridDrillingEngineer.ItemsSource = _userWellCustomFields;

Get the binding object and force a refresh:

        var bindingSource = TheDataGrid.GetBindingExpression(DataGrid.ItemsSourceProperty);
        bindingSource.UpdateSource();