private static IntPtr WindowProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
{
IntPtr oldWndProc = GetProp(hWnd, "SystemMenu");
try
{
switch (msg)
{
case WM_DESTROY:
//Automatically uninstall ourself upon Form close
SetWindowLongPtr(hWnd, GWL_WNDPROC, oldWndProc);
break;
case WM_SYSCOMMAND:
//if (wParam.ToInt32() >= SC_MENUSTART) break;
IntPtr handler = GetProp(hWnd, "SystemMenuHandler");
if (handler != IntPtr.Zero)
{
//SystemMenuHandler syshandler = Marshal.GetDelegateForFunctionPointer(handler, typeof(SystemMenuHandler)) as SystemMenuHandler; //This only works for static methods!
SystemMenuHandler syshandler = GCHandle.FromIntPtr(handler).Target as SystemMenuHandler;
if (syshandler.Invoke(wParam.ToInt32()))
{
return(IntPtr.Zero);
}
}
break;
}
}
catch
{
//if we get an unhandled error, uninstall ourself.
SetWindowLongPtr(hWnd, GWL_WNDPROC, oldWndProc);
}
return(CallWindowProc(oldWndProc, hWnd, msg, wParam, lParam));
}
/// <summary>
/// Assign a handler for the system menu events. There can only be one.
/// Any previously set handler will be replaced. This cannot be called
/// in the constructor because the underlying Win32 window has not yet
/// been created. Should be called during the Form.Load event.
/// </summary>
/// <param name="form">form to assign the handler to</param>
/// <param name="handler">Delegate handler to handle the events</param>
public static void SetHandler(Form form, SystemMenuHandler handler)
{
IntPtr hWnd = form.Handle;
if (hWnd == null || hWnd == IntPtr.Zero)
{
return;
}
//IntPtr handle = Marshal.GetFunctionPointerForDelegate(handler); //This only works for static methods!
IntPtr handle = GCHandle.ToIntPtr(GCHandle.Alloc(handler));
SetProp(hWnd, "SystemMenuHandler", handle);
if (GetProp(hWnd, "SystemMenu") != IntPtr.Zero)
{
return; //Only subclass once!
}
IntPtr wndProcPtr = Marshal.GetFunctionPointerForDelegate(_wndProc);
SetProp(hWnd, "SystemMenu", SetWindowLongPtr(hWnd, GWL_WNDPROC, wndProcPtr));
}
