Winforms：如何使用 ToolStripDropDown 模拟 AutoClose

Question

我目前正在编写一个组合框，用我自己的替换建议下拉列表。为此，我创建了一个 ToolStripDropDown，我用一个列表框填充它。当用户在组合框文本字段中键入文本时，此列表框会更新。

我的问题是，如果我将 ToolStripDropDown 的 AutoClose 属性设置为 true，似乎即使文本字段具有焦点，ToolStripDropDown 也会“窃取”很多消息，包括键盘消息。

如果我将 AutoClose 属性设置为 false，则一切正常。但下拉菜单不会关闭，例如，如果用户在组合之外点击。

我想知道自己做“自动关闭”，但我不确定如何实现它。关于如何做到这一点的任何想法？

Answer 1

我找到了解决方案。查看 ToolStripManager 代码（感谢 ReSharper！），我发现当 AutoClose 设置为 true 时，管理器正在监视应用程序消息，以便检测用户何时在下拉列表之外单击。我已经通过以下方式调整了他们的代码：

class MyComboBox : ComboBox, IMessageFilter
{
        private ToolStripDropDown m_dropDown;

        MyComboBox()
        {
            ...
            Application.AddMessageFilter(this);
            ...
        }

        protected override void Dispose(bool disposing)
        {
            ...
            Application.RemoveMessageFilter(this);
            base.Dispose(disposing);
        }


        private const int WM_LBUTTONDOWN = 0x0201;
        private const int WM_RBUTTONDOWN = 0x0204;
        private const int WM_MBUTTONDOWN = 0x0207;
        private const int WM_NCLBUTTONDOWN = 0x00A1;
        private const int WM_NCRBUTTONDOWN = 0x00A4;
        private const int WM_NCMBUTTONDOWN = 0x00A7;

        [DllImport("user32.dll", ExactSpelling = true, CharSet = CharSet.Auto)]
        [ResourceExposure(ResourceScope.None)]
        public static extern int MapWindowPoints(IntPtr hWndFrom, IntPtr hWndTo, [In, Out] ref Point pt, int cPoints);

        public bool PreFilterMessage(ref Message m)
        {
            if (m_dropDown.Visible)
            {
                switch (m.Msg)
                {
                    case WM_LBUTTONDOWN:
                    case WM_RBUTTONDOWN:
                    case WM_MBUTTONDOWN:
                    case WM_NCLBUTTONDOWN:
                    case WM_NCRBUTTONDOWN:
                    case WM_NCMBUTTONDOWN:
                        //
                        // When a mouse button is pressed, we should determine if it is within the client coordinates
                        // of the active dropdown.  If not, we should dismiss it.
                        //
                        int i = unchecked((int)(long)m.LParam);
                        short x = (short)(i & 0xFFFF);
                        short y = (short)((i >> 16) & 0xffff);
                        Point pt = new Point(x, y);
                        MapWindowPoints(m.HWnd, m_dropDown.Handle, ref pt, 1);
                        if (!m_dropDown.ClientRectangle.Contains(pt))
                        {
                            // the user has clicked outside the dropdown
                            pt = new Point(x, y);
                            MapWindowPoints(m.HWnd, Handle, ref pt, 1);
                            if (!ClientRectangle.Contains(pt))
                            {
                                // the user has clicked outside the combo
                                hideDropDown();
                            }
                        }
                        break;
                }
            }
            return false;
        }
}