c# - 用户控件 : How to add MouseWheel Listener?

Question

我正在创建一个 UserControl，它应该在鼠标悬停在控件上并且 MouseWheel 旋转时使用react。

目前我正在这样做，如下所示:

    public MyUserControl()
    {
        this.MouseWheel += new MouseEventHandler(MouseWheelHandler);
    }

    private void MouseWheelHandler(object sender, System.Windows.Forms.MouseEventArgs e)
    {
        if (e.Delta > 0)
            incIndex();

        if (e.Delta < 0)
            decIndex();
    }

    protected override void OnMouseEnter(EventArgs e)
    {
        this.Focus();

        base.OnMouseEnter(e);
    }

事实上这工作正常，但问题是“this.Focus();”部分因为它破坏了我的表单/应用程序行为。

有没有更好的方法来实现这一目标？

Answer 1

有同样的问题，我最终实现了@Paul_Westcott 和@nr1 的混合解决方案。这是一个类似于@Paul_Westcott 的解决方案的本地解决方案(仅适用于订阅的 winforms 控件)。它是多显示器安全和 MDI 安全的(与应用程序中的其他窗口重叠)

public static class MouseWheelHandlerForWinformsControl
{
    private class MouseWheelMessageFilter : IMessageFilter
    {
        [DllImport("user32.dll")]
        private static extern IntPtr WindowFromPoint(Point pt);

        private readonly Control mCtrl;
        private readonly Action<MouseEventArgs> mOnMouseWheel;

        public MouseWheelMessageFilter(Control ctrl, Action<MouseEventArgs> onMouseWheel)
        {
            mCtrl = ctrl;
            mOnMouseWheel = onMouseWheel;
        }

        public bool PreFilterMessage(ref Message m)
        {
            // handle only mouse wheel messages
            if (m.Msg != 0x20a)
                return false;

            Point mouseAbsolutePosition = new Point(m.LParam.ToInt32());
            Point mouseRelativePosition = mCtrl.PointToClient(mouseAbsolutePosition);

            IntPtr hControlUnderMouse = WindowFromPoint(mouseAbsolutePosition);
            Control controlUnderMouse = Control.FromHandle(hControlUnderMouse);

            if (controlUnderMouse != mCtrl)
                return false;

            MouseButtons buttons = GetMouseButtons(m.WParam.ToInt32());
            int delta = m.WParam.ToInt32() >> 16;

            var e = new MouseEventArgs(buttons, 0, mouseRelativePosition.X, mouseRelativePosition.Y, delta);

            mOnMouseWheel(e);

            return true;
        }

        private static MouseButtons GetMouseButtons(int wParam)
        {
            MouseButtons buttons = MouseButtons.None;

            if(HasFlag(wParam, 0x0001)) buttons |= MouseButtons.Left;
            if(HasFlag(wParam, 0x0010)) buttons |= MouseButtons.Middle;
            if(HasFlag(wParam, 0x0002)) buttons |= MouseButtons.Right;
            if(HasFlag(wParam, 0x0020)) buttons |= MouseButtons.XButton1;
            if(HasFlag(wParam, 0x0040)) buttons |= MouseButtons.XButton2;

            return buttons;
        }

        private static bool HasFlag(int input, int flag)
        {
            return (input & flag) == flag;
        }
    }

    public static void MemorySafeAdd(Control ctrl, Action<MouseEventArgs> onMouseWheel)
    {
        if (ctrl == null || onMouseWheel == null)
            throw new ArgumentNullException();

        var filter = new MouseWheelMessageFilter(ctrl, onMouseWheel);
        Application.AddMessageFilter(filter);
        ctrl.Disposed += (s, e) => Application.RemoveMessageFilter(filter);
    }
}

将此帮助程序类添加到您的解决方案后，您可以在一行中将控件 myControl 订阅到鼠标滚轮，如下所示:

public void Init() {
    MouseWheelHandlerForWinformsControl.MemorySafeAdd(myControl, OnMouseWheelEvent);
}

void OnMouseWheelEvent(MouseEventArgs args) {
    // do what you need here
}