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How is this not causing a cross thread exception in silverlight?
private void UserControl_Loaded(object sender, RoutedEventArgs e)
{
    QueryTask queryTask = new QueryTask(URL);
    queryTask.ExecuteCompleted += new EventHandler<QueryEventArgs>(queryTask_ExecuteCompleted);
    queryTask.Failed += new EventHandler<TaskFailedEventArgs>(queryTask_Failed);
    Query query = new Query();
    query.Where = "Field <> 'XXX'";
    query.OutFields.Add("*");
    queryTask.ExecuteAsync(query);
    BuildingsOrganizationList.ItemsSource = organizationList;
}


void queryTask_ExecuteCompleted(object sender, QueryEventArgs e)
{
    FeatureSet featureSet = e.FeatureSet;
    foreach (KeyValuePair<string, string> columns in featureSet.FieldAliases)
    {
        TypeGrid.Columns.Add(new DataGridTextColumn()
        {
            Header = columns.Key,
            Binding = new System.Windows.Data.Binding("Attributes[" + columns.Key + "]"),
            CanUserSort = true
        });
    }
    TypeGrid.ItemsSource = featureSet.Features;
    TypeBusyIndicator.IsBusy = false;

    testing();
}

private void testing()
{
    List<string> temp = new List<string>();
    temp.Add("Item 1");
    temp.Add("Item 2");
    temp.Add("Item 3");

    foreach (string org in temp)
    {
        organizationList.Add(org);
    }
}

Task.Factory.StartNew(() =>
{
    //code of queryTask_ExecuteCompleted here
});