How do I filter ToolStripMenuItem mouse events in a Winforms application?

Question

I have a .Net Winforms application with a ToolStrip that contains several ToolStripMenuItems.

I would like to be able to intercept Mouse LButton down events on the ToolStripMenuItems. I have PreFilterMessage defined. I assume I should be able to capture the event in that filter.

bool IMessageFilter.PreFilterMessage(ref Message message)
{
    switch (message.Msg)
    {
    }
}

How would I do that?

Is there a custom message being used?

Once I capture the message, how can I use the Message data to get the actual ToolStripMenuItem that was clicked?

You can, but I'm not sure it's the best solution for the problem you are trying to solve. What's the actual problem you are trying to solve? Why you are not using [ItemClicked](https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.toolstrip.itemclicked?view=windowsdesktop-8.0&WT.mc_id=DT-MVP-5003235) event? — Reza Aghaei, Mar 23 '23 at 03:03
@Reza, no that's exactly what I need to be doing to generically catch windows events across all control types (including menu items). — JohnB, Mar 23 '23 at 14:13
'*generically catch windows events across all control types*'<- It's a solution, right? I'm curious to know the actual requirement. There might be better solutions, for example: [Using UI automation or a Windows hook to get clicks](https://stackoverflow.com/a/72005695/3110834). — Reza Aghaei, Mar 23 '23 at 23:58
Or you may be able to [subscribe to the desired events](https://stackoverflow.com/a/39018993/3110834) in a base form. — Reza Aghaei, Mar 23 '23 at 23:59

dr.null · Accepted Answer · 2023-03-24T16:49:36.367

In the IMessageFilter implementation, use the m.HWnd property to get the owner control of the clicked ToolStripItem by calling the Control.FromHandle method and cast it to a proper strip type. To the base ToolStrip class or one of its derives.

Get the clicked point from the m.LParam property to search the strip's Items collection and find the clicked item whose bounds should contain that point if any.

// +
using System.Linq;

public partial class SomeForm : Form, IMessageFilter
{
    const int WM_LBUTTONDOWN = 0x0201;

    public SomeForm()
    {
        InitializeComponent();
        // ...
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        Application.AddMessageFilter(this);
    }

    protected override void OnFormClosing(FormClosingEventArgs e)
    {
        Application.RemoveMessageFilter(this);
        base.OnFormClosing(e);
    }

    public bool PreFilterMessage(ref Message m)
    {
        if (m.Msg == WM_LBUTTONDOWN && FromHandle(m.HWnd) is ToolStrip ts)
        {
            var p = PointToClient(PointToScreen(new Point(m.LParam.ToInt32())));
            var item = ts.Items.Cast<ToolStripItem>()
                .FirstOrDefault(x => x.Bounds.Contains(p));

            if (item != null)
            {
                Console.WriteLine(item.Text);
                // ...
            }
        }

        return false;
    }
}

If you just need to handle the items of the dropdown menus, then change the type of the owner control from the base ToolStrip to the derived ToolStripDropDownMenu.

if (m.Msg == WM_LBUTTONDOWN && FromHandle(m.HWnd) is ToolStripDropDownMenu ts)
{
    // The same ...
}

Or check the type of the returned item to also skip types like ToolStripSeparator.

if (item is ToolStripMenuItem)
{
    Console.WriteLine(item.Text);
    // ...
}

Find out a different approach here.

Thx for the reply. I have the MessageFilter implemented and am capturing required events on all Controls. What I'd like to do is catch the actual MenuItem events as a user clicks through ToolStripMenuItems - as in what SPECIFIC MenuItems are being clicked/selected. — JohnB, Mar 23 '23 at 14:12

How do I filter ToolStripMenuItem mouse events in a Winforms application?

1 Answers1