将拖拽进行到底 – 终结篇 WindowsMessage

在《将拖拽进行到底》这篇文（http://www.zhangsichu.com/blogview.asp?Content_Id=15）中的第四种方法，发一个消息告诉系统鼠标在CaptionTitle（每个窗口自己TitleBar）上，这样窗口的拖拽就可以由系统托管了。现在实现了在窗口中任意位置单击鼠标拖拽窗体。这两天，我又发现了一个东东，几乎可以完美的实现这个思想，用SendMessage(WM_NCLBUTTONDOWN, HTCAPTION, MAKELPARAM( point.x, point.y))或者用UINT CMFCDragDlg::OnNcHitTest(CPoint point)直接返回HTCAPTION。SendMessage的思想是窗口拖拽就直接由系统托管，不管鼠标点击到那里，都告诉系统，鼠标在窗体的CaptionBar上—发伪装的消息。用UINT CMFCDragDlg::OnNcHitTest(CPoint point)的含义是，直接处理系统的Message，不让系统托管了。在MFC中这两种方法的处理和实现有很多文章在介绍了，这里就不写了。这里就在C#下用类似的方法，来实现SendMessage(WM_NCLBUTTONDOWN, HTCAPTION, MAKELPARAM( point.x, point.y))和UINT CMFCDragDlg::OnNcHitTest(CPoint point)。
SendMessage(WM_NCLBUTTONDOWN, HTCAPTION, MAKELPARAM( point.x, point.y)) 方案：
Override WndProc 方法当有WM_LBUTTONDOWN消息时处理。
protected override void WndProc(ref Message m)
    {
      Point screenPoint= Control.MousePosition;
      Point clientPoint = this.PointToClient(screenPoint);
      if (m.Msg == UnmanagedMethods.WM_LBUTTONDOWN)
      {

        if(rectangleMin.Contains(clientPoint))
        {
          this.WindowState = FormWindowState.Minimized;
          return;
        }
        if(rectangleClose.Contains(clientPoint))
        {
          this.Close();
          return;
        }
        UnmanagedMethods.SendMessage(this.Handle, UnmanagedMethods.WM_NCLBUTTONDOWN, UnmanagedMethods.HTCAPTION, 0);
        = UnmanagedMethods.MakeLParam(screenPoint.X,clientPoint.Y);
        return;
      }
      base.WndProc (ref m);
    }

UnmanagedMethods.SendMessage(this.Handle, UnmanagedMethods.WM_NCLBUTTONDOWN, UnmanagedMethods.HTCAPTION, 0);
        = UnmanagedMethods.MakeLParam(screenPoint.X,clientPoint.Y);
        return;
发消息告诉系统自己在CaptionBar上。

UINT CMFCDragDlg::OnNcHitTest(CPoint point) 方案：
自己处理消息，自己修改截获的消息，然后还给系统，告诉系统自己在CaptionBar上。

    protected override void WndProc(ref Message m)
    {
      Point screenPoint= Control.MousePosition;
      Point clientPoint = this.PointToClient(screenPoint);
      if (m.Msg == UnmanagedMethods.WM_LBUTTONDOWN)
      {

        if(rectangleMin.Contains(clientPoint))
        {
          this.WindowState = FormWindowState.Minimized;
          return;
        }
        if(rectangleClose.Contains(clientPoint))
        {
          this.Close();
          return;
        }
        m.WParam = new IntPtr(UnmanagedMethods.HTCAPTION);
        m.Msg = UnmanagedMethods.WM_NCLBUTTONDOWN;
        m.LParam = UnmanagedMethods.MakeLParam(screenPoint.X,clientPoint.Y);
        }
      base.WndProc (ref m);
    }

在Windows 2003 Server Enterprise Edition + VS 2003 Enterprise Edition 编译通过没有问题。

File: 本文实例代码