Code

  private void diagram1_NodeCreated(object sender, NodeEventArgs e)
	  {
		ShapeNode node = e.Node as ShapeNode;
		if (!zoomToRectTool && node != null)
		{
		    diagram1.Invalidate();
		    diagramView1.ZoomToRect (node.Bounds);
		   //tried here diagram1.Invalidate();

		    diagram1.Nodes.Remove(node);
		    zoomToRectTool = true;
		    diagramView1.ShowScrollbars = true;

		}
		else
		{
		    diagram1.Nodes.Remove(node);
		}
	  }
 

Code

 private void diagramView1_Paint(object sender, PaintEventArgs e)
	  {
		System.Drawing.Brush textBrush = new System.Drawing.SolidBrush(Color.Black);
		System.Drawing.Brush backBrush = diagram1.BackBrush.CreateGdiBrush(diagram1.Bounds);

		foreach (DiagramLink l in diagram1.Links)
		{
		    int s = l.SegmentCount / 2;
		    PointF p1 = l.ControlPoints[s];
		    PointF p2 = l.ControlPoints[s + 1];
		    float iX;
		    if (p2.X < p1.X)
			  iX = p2.X + 10F;
		    else if (p2.X > p1.X)
			  iX = p2.X - 10F;
		    else
			  iX = (p1.X + p2.X) / 2;
		    PointF c = new PointF(iX, (p1.Y + p2.Y) / 2);//(p1.X + p2.X) / 2

		    SizeF textSize = diagram1.MeasureString(l.Text, l.Font, int.MaxValue, StringFormat.GenericDefault);
		    float w = textSize.Width;
		    float h = textSize.Height;
		    RectangleF textRect = new RectangleF(c.X - w / 2, c.Y - h / 2, w, h);

		    StringFormat stringFormat = new StringFormat();
		    stringFormat.Alignment = StringAlignment.Center;
		    stringFormat.LineAlignment = StringAlignment.Center;


		    e.Graphics.FillRectangle(backBrush, textRect);
		    e.Graphics.DrawString(l.Text, l.Font, textBrush, textRect, stringFormat);

		}

		backBrush.Dispose();
		textBrush.Dispose();

	  }