Make MouseWheel event pass from child to parent

Question

I have a Panel where AutoScroll is true. This panel contains many smaller panels that fill all available space like tiles. When there are too many sub-panels to display I get the vertical scroll bar as expected.
Each of these "tiles" have some event handlers tied to them to handle MouseDown / MouseUp / MouseMove as they can be dragged around.

The problem I'm having is that mouse wheel scroll doesn't work on the parent panel as it won't have focus. I can't give it focus because in all probability I'll be scrolling while moving a sub-panel which will have the focus instead, and even then that would require workarounds since panels don't like focus.

I've been trying (and failing) to find a way to propagate only mousewheel events from the children to the parent.
I've read that in Winforms if a control cannot handle a mouse event it will bubble it up to the parent of that control, and then to the parent of that control and so on until it finds a suitable handler.
With this in mind I figured the best solution would be to use WndProc to override all scroll related events on the sub-panel and pass them to the parent while leaving all other events intact but admittedly this isn't my strong suit and I'm lost.

I've tried a few other solutions such as making the sub-panels invisible to all mouse events but as you might have guessed this was bad. I've read about implementing a message filter but didn't understand it.

Here's the code that will give you a very basic example of the panel and its children:

private void Form1_Load(object sender, EventArgs e)
{
    Height = 600;
    Width = 300;

    Color[] colors = new Color[]{ Color.PowderBlue, Color.PeachPuff };

    Panel panel = new Panel()
    {
        Height = this.ClientSize.Height - 20,
        Width = 200,
        Top = 10,
        Left = 10,
        BackColor = Color.White,
        BorderStyle = BorderStyle.FixedSingle,
        AutoScroll = true
    };

    for (int i = 0; i < 10; i++)
    {
        Panel subPanel = new Panel()
        {
            Name = @"SubPanel " + i.ToString(),
            Height = 100,
            Width = panel.Width - System.Windows.Forms.SystemInformation.VerticalScrollBarWidth - 2,
            BackColor = colors[i % 2],
            Top = i * 100
        };
        subPanel.MouseClick += subPanel_MouseClick;
        panel.Controls.Add(subPanel);
    }

    Controls.Add(panel);
}

void subPanel_MouseClick(object sender, MouseEventArgs e)
{
    Panel panel = sender as Panel;
    Text = panel.Name;
}

Here's my attempt at overriding WndProc in a custom panel:

class NoScrollPanel : Panel
{
    private const int WM_HSCROLL = 0x114;
    private const int WM_VSCROLL = 0x115;
    private const int MOUSEWHEEL = 0x020A;
    private const int KEYDOWN = 0x0100;

    protected override void WndProc(ref Message m)
    {
        if ((m.HWnd == Handle) && (m.Msg == MOUSEWHEEL || m.Msg == WM_VSCROLL || (m.Msg == KEYDOWN && (m.WParam == (IntPtr)40 || m.WParam == (IntPtr)35))))
        {
            PostMessage(Parent.Handle, m.Msg, m.WParam, m.LParam);
        }
        else
        {
            base.WndProc(ref m);
        }
    }

    [DllImport("User32.dll")]
    private static extern IntPtr PostMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);
}

Any help or alternative approaches are most welcome. Thanks!

Answer 1

At my side @a-clymer's solution does not work, perhaps different environment. Currently there is no direct, clear answer for my problem so I try to combine several thoughts of other professionals and succeed.

In my current project, I have a few input controls contained in a Panel. I managed to make the mouse wheel scroll the panel instead of the ComboBox items by creating a child class of ComboBox and override its WndProc:

public class ComboBoxWithParentMouseWheel : ComboBox
{
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);

    const int WM_MOUSEWHEEL = 0x020A;

    //thanks to a-clymer's solution
    protected override void WndProc(ref Message m)
    {
        if (m.Msg == WM_MOUSEWHEEL)
        {
            //directly send the message to parent without processing it
            //according to https://stackoverflow.com/a/19618100
            SendMessage(this.Parent.Handle, m.Msg, m.WParam, m.LParam);
            m.Result = IntPtr.Zero;
        }else base.WndProc(ref m);
    }
}

Answer 2

All credit goes to Hans Passant (again), taken from the thread he suggested: https://stackoverflow.com/a/3562449/17034

Allowing the the containing panel to take focus worked fine. For the demo code above the class needs no changes, just use it for only the containing panel. I had to make some tweaks to my project to call focus when necessary, but it was far from rocket science.

Thanks again.

Answer 3

I could not get any of these solutions to work. I am overriding the WndProc fxn just like you. Finally found the solution! I noticed that if the container holding my TextBox was in focus, then the scroll worked, just not when the TextBox was in focus.

I didn't need to change the transparency of the event, I needed to send the event to a different Control Handle! (It seems so simple now, but I've trying to figure this out for days!)

internal class myTextBox : TextBox
{
    const int WM_MOUSEWHEEL = 0x020A;

    protected override void WndProc(ref Message m)
    {

        if (m.Msg == WM_MOUSEWHEEL)
            m.HWnd = this.Parent.Handle; // Change the Handle of the message

        base.WndProc(ref m);
    }
}

I haven't seen any mention of this method in all my Google searches, if there is some reason NOT to do this I hope someone will reply.

Answer 4

An improved version of @a-clymer version that works better.

const int WM_MOUSEWHEEL = 0x020A;

if (m.Msg == WM_MOUSEWHEEL)
{
    // find the first scrollable parent control
    Control p = this;
    do
    {
        p = p.Parent;
    } while (p != null && !(p is ScrollableControl));

    // rewrite the destination handle of the message
    if (p != null)
        m.HWnd = p.Handle;
}