AutoCAD Civil 3D :: Force Refresh Is Not Working?

I am trying  to make a simple app using .NET classes.

I made a simple Windows.Form in which are check boxes (on for each layer of the CAD drawing).

Just to set the visibility of each layer. Everything is working fine, but I have a little problem with refreshing a drawing.

Changes of visibility settings are applied  after a form is closed.

I need the drawing to be refreshed after every check box check change.

 I enclose a method with handles check boxes changes. 

private void LayerCheckedChanged(object sender, EventArgs e)
{
CheckBox s = sender as CheckBox;

[Code].....