/// <summary>
/// Invokes the default window procedure associated with this window.
/// </summary>
/// <param name="m">A <see cref="System.Windows.Forms.Message" /> that is associated with the current Windows message. </param>
protected override void WndProc(ref Message m)
{
switch (m.Msg)
{
//Do all painting in WM_PAINT to reduce flicker.
case (int)WindowsMessage.WM_ERASEBKGND:
return;
case (int)WindowsMessage.WM_PAINT:
// This code is influenced by Steve McMahon's article:
// "Painting in the MDI Client Area".
// http://vbaccelerator.com/article.asp?id=4306
// Use Win32 to get a Graphics object.
var paintStruct = new PAINTSTRUCT();
var screenHdc = NativeMethods.BeginPaint(m.HWnd, ref paintStruct);
using (var screenGraphics = Graphics.FromHdc(screenHdc))
{
// Get the area to be updated.
var clipRect = new Rectangle(
paintStruct.rcPaint.Left,
paintStruct.rcPaint.Top,
paintStruct.rcPaint.Right - paintStruct.rcPaint.Left,
paintStruct.rcPaint.Bottom - paintStruct.rcPaint.Top);
// Double-buffer by painting everything to an image and
// then drawing the image.
var width = (MdiClient.ClientRectangle.Width > 0 ? MdiClient.ClientRectangle.Width : 0);
var height = (MdiClient.ClientRectangle.Height > 0 ? MdiClient.ClientRectangle.Height : 0);
using (Image i = new Bitmap(width, height))
{
using (var g = Graphics.FromImage(i))
{
// This code comes from J Young's article:
// "Generating missing Paint event for TreeView and ListView".
// http://www.codeproject.com/cs/miscctrl/genmissingpaintevent.asp
// Draw base graphics and raise the base Paint event.
var hdc = g.GetHdc();
var printClientMessage =
Message.Create(m.HWnd, (int)WindowsMessage.WM_PRINTCLIENT, hdc, IntPtr.Zero);
DefWndProc(ref printClientMessage);
g.ReleaseHdc(hdc);
// Draw the image here.
if (image != null)
{
DrawImage(g, clipRect);
}
// Call our OnPaint here to draw graphics over the
// original and raise our Paint event.
OnPaint(new PaintEventArgs(g, clipRect));
}
// Now draw all the graphics at once.
screenGraphics.DrawImage(i, MdiClient.ClientRectangle);
}
}
NativeMethods.EndPaint(m.HWnd, ref paintStruct);
return;
case (int)WindowsMessage.WM_SIZE:
// Repaint on every resize.
MdiClient.Invalidate();
break;
case (int)WindowsMessage.WM_NCCALCSIZE:
// If AutoScroll is set to false, hide the scrollbars when the control
// calculates its non-client area.
if (!autoScroll)
{
ShowScrollBar(m.HWnd, SB.SB_BOTH, 0 /*false*/);
}
break;
}
base.WndProc(ref m);
}
