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How do I provide a 1 pixel border in the NonClient area of my Control?

Platform: WinForms| Category: Controls

You will have to first provide some space in the NC area by setting the WS_BORDER flag in CreateParams and then draw the border yourself by listening to the WM_NCPAINT message in your Control, as follows:


		protected override CreateParams CreateParams
		{
			get 
			{
				System.Windows.Forms.CreateParams cp = base.CreateParams;
				if(this.needFlatBorder)
				{
					cparams.ExStyle &= ~512 /*WS_EX_CLIENTEDGE*/;
					cparams.Style &= ~8388608 /*WS_BORDER*/;
					cp.Style |= 0x800000; // WS_BORDER
				}
			}
		}

		protected override void WndProc(ref Message m)
		{
			if(m.Msg == 133/*WM_NCPAINT*/)
			{
				this.DrawFlatNCBorder(ref m);
			}
			base.WndProc(ref m);
		}

		private void DrawFlatNCBorder(ref Message msg)
		{
			IntPtr hRgn1 = (IntPtr) msg.WParam; 
			// The update region is clipped to the window frame. When wParam is 1, the entire window frame needs to be updated.

			IntPtr hdc = NativeMethods.GetDCEx(msg.HWnd, hRgn1, 1/*DCX_WINDOW*/|0x0020/*DCX_PARENTCLIP*/);
			if (hdc != IntPtr.Zero)
			{
				using (Graphics g = Graphics.FromHdc(hdc))
				{

					Rectangle bounds = new Rectangle(0,0,this.Width,this.Height);
			
					ControlPaint.DrawBorder(g,bounds,this.borderColor,ButtonBorderStyle.Solid);

					// create a clipping region for remaining parts to be drawn excluding
					// the border we did just drew
					bounds.Inflate(-1, -1);
					IntPtr hRgn2 = NativeMethods.CreateRectRgn(bounds.Left, bounds.Top, bounds.Right, bounds.Bottom);

					if(hRgn2 == (IntPtr)1)
					{
						// Provide a new clipping region.
						msg.WParam = (IntPtr) hRgn2;
					}
					else
					{
						// combine with existing clipping region.
						NativeMethods.CombineRgn(hRgn1, hRgn1, hRgn2, NativeMethods.RGN_AND);
						NativeMethods.DeleteObject(hRgn2);
					}
				}

				msg.Result = (IntPtr) 1;
				NativeMethods.ReleaseDC(msg.HWnd, hdc);
		
			}			
			Invalidate();
		}

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