Rhino inside winform issue

Hi Everyone
I am trying to build one app base on Rhino inside and winform. but when I draw meshes in viewportcontrol, nothing change in the UI and no return error. This is my code as follow, Please give me some clue. thanks.

 if (_forwardKinematics.Robot.Meshes != null)
            {
                // Initiate the display color and transparancy of the robot mesh
                System.Drawing.Color color;
                double trans;
                // Set the display color and transparancy of the robot mesh
                if (_forwardKinematics.InLimits == true)
                {
                    color = System.Drawing.Color.FromArgb(225, 225, 225);
                    trans = 0.0;
                }
                else
                {
                    color = System.Drawing.Color.FromArgb(150, 0, 0);
                    trans = 0.5;
                }

                for (int i = 0; i != _forwardKinematics.Robot.Meshes.Count; i++)
                {
                    viewportControl1.Display.DrawMeshShaded(_forwardKinematics.Robot.Meshes[i], new Rhino.Display.DisplayMaterial(color, trans));       
                }
                viewportControl1.Viewport.ZoomExtents();
                viewportControl1.Refresh();
                //UseWaitCursor = false;
            }