Refresh DataGrid MVVM Silverlight - silverlight-4.0

Question

I have got a Silverlight Page which contains a DataGrid .It is bound to a ViewModel.On the initialization of the ViewModel I have called a RIA Services to fetch all records from database.I have another button on the page which opens a child form on click.This child form contains DataForm which adds a record to the database and after successfully adding the record again I fetched all the record using RIA Services and RaisedPropertyChanged event.But the DataGrid does not shows the new record.What is the problem and why the DataGrid is not getting refreshed...The code of view and viewmodel is written below.
//XAML of View
<sdk:DataGrid x:Name="grd_classes" ItemsSource="{Binding Classes,Mode=TwoWay}" AutoGenerateColumns="False" Width="300" Grid.Column="1" >
<sdk:DataGrid.Columns>
<sdk:DataGridTextColumn Header="Class Name" Width="140" Binding="{Binding Name,Mode=TwoWay}" CanUserReorder="True" CanUserResize="True" CanUserSort="True" />
<sdk:DataGridTextColumn Header="Alias" Width="140" Binding="{Binding Alias,Mode=TwoWay}" CanUserReorder="True" CanUserResize="True" CanUserSort="True" />
</sdk:DataGrid.Columns>
</sdk:DataGrid>
//Code of viewmodel
namespace SMS.ViewModel
{
public class ClassesViewModel:ViewModel
{
private ClassesContext _context = new ClassesContext();
public ClassesViewModel()
{
_context.Load<Class>(_context.GetClassesQuery(), OnLoad, true);
}
public EntitySet<Class> Classes
{
get
{
return _context.Classes;
}
}
public void AddNewClass(object parameter)
{
for (int i = 0; i <= newClass.Count - 1;i++ )
{
_context.Classes.Add(newClass[i]);
}
_context.SubmitChanges(OnSave,null);
}
private void OnLoad(LoadOperation op)
{
if (!op.HasError)
{
RaisePropertyChanged("Classes");
}
}
private void OnSave(SubmitOperation op)
{
if (op.IsComplete)
{
if (op.HasError)
{
MessageBox.Show("Error");
}
else
{
_context = new ClassesContext();
_context.Load<Class>(_context.GetClassesQuery(), OnLoad, true);
DialogResult = true;
}
}
}
}
}

Answer 1

have you set grd_classes DataContext ? also need RaisePropertychanged event as well
_context.Load<Class>(_context.GetClassesQuery(), OnLoad, true);
RaisePropertyChanged(() => Classes);