Windows Forms: ctrl button prevents ListView from scrolling with mouse wheel

Question

I want to scroll ListView with mouse wheel while Ctrl button is pressed. But apparently pressing Ctrl changes scroll behavior: it stops scrolling, possibly tries to apply some zooming logic, I don't know. And I can't find out how to override that. Please any help or suggestions?

Answer 1

The solution to get mouse wheel scrolling working while Ctrl key is held down is to listen for the WndProc event and specifically detecting MOUSEWHEEL trigger, minimum simple working example:

ListBox with WndProc override

class CtrlListBoxScroll : ListBox
{
    private const int WM_HSCROLL = 0x114;
    private const int WM_VSCROLL = 0x115;
    private const int WM_MOUSEWHEEL = 0x20A;

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == WM_MOUSEWHEEL)
        {
            var scrollDirection = NativeMethods.GET_WHEEL_DELTA_WPARAM(m.WParam);
            // scrolling down
            if (this.TopIndex < this.Items.Count && scrollDirection < 0)
            {
                this.TopIndex += 1;
            }
            // scrolling up
            if (this.TopIndex > 0 && scrollDirection > 0)
            {
                this.TopIndex -= 1;
            }
        }
    }
}

NativeMethods to read the wParam and detect scroll direction

internal static class NativeMethods
{
    internal static ushort HIWORD(IntPtr dwValue)
    {
        return (ushort)((((long)dwValue) >> 0x10) & 0xffff);
    }

    internal static ushort HIWORD(uint dwValue)
    {
        return (ushort)(dwValue >> 0x10);
    }

    internal static int GET_WHEEL_DELTA_WPARAM(IntPtr wParam)
    {
        return (short)HIWORD(wParam);
    }

    internal static int GET_WHEEL_DELTA_WPARAM(uint wParam)
    {
        return (short)HIWORD(wParam);
    }
}

Then finally testing it

private void Form1_Load(object sender, EventArgs e)
{
    var ctrlListBoxScroll = new CtrlListBoxScroll();
    ctrlListBoxScroll.Items.AddRange
    (
        new object[]
        {
            "hello", "scroll", "bar", "pressing", "ctrl", "to scroll",
            "this", "list", "box", "check", "ctrl", "key", "is", "held"
        }
    );
    this.Controls.Add(ctrlListBoxScroll);
}