Adding a right-click Context Menu on a ToolStripMenuItem, without closing the Menu

Question

My application has a menu at the top.
The first item in the menu (File) has the usual New, Open..., Save, Save As... as well as Open Recent. This last one is a ToolStripDropDown showing a most-recently-used list of filenames.

I would like to add a right-click Context Menu (not a sub-menu) to the file names which will have one item in the context menu, to remove the right-clicked filename from the list.

I load the file names into the Menu as follows:

private void mnuFile_DropDownOpened(object sender, EventArgs e)
{
    foreach (string fn in mru_files)
    {
        ToolStripMenuItem p = new ToolStripMenuItem(fn);
        p.Click += fn_clicked;
        p.MouseDown += fn_MouseDown;
        openRecentToolStripMenuItem.DropDownItems.Add(p);
    }
}

The main portion of this works fine - the fn_clicked method is invoked when I click on a file and it will do what it's supposed to do.

In the MouseDown Handler I can remove the file from the list as follows:

private void fn_MouseDown(object sender, MouseEventArgs e)
{
    ToolStripMenuItem toolStripMenuItem = sender as ToolStripMenuItem;

    if (toolStripMenuItem != null
        && e.Button == System.Windows.Forms.MouseButtons.Right
        && mru_files.Find(x => x == toolStripMenuItem.Text) != null)
    {
        mru_files.Remove(toolStripMenuItem.Text);
    }
}

but this doesn't show a menu.

If I add a context menu to the form, and do

mnu_ctxMRUitem.Show(xyz, e.X, e.Y);

instead of removing the file, I get the Context Menu in the right place, but the original menu with the list of files has disappeared.

How can I show the context menu on right-click of a menu item, without the main menu disappearing.

Answer 1

To force a ToolStripDropDown to remain opened, you can set its AutoClose property to false.
You can then show a ContextMenuStrip in the location where the right-click was generated.

Subscribe to the MouseUp Event of any ToolStripMenuItem that requires a ContextMenuStrip and, if the e.Button == MouseButtons.Right test is positive, block the ToolStripDropDown that is the Owner of the ToolStripMenuItem selected.
Use the same MouseUp Event Handler for all ToolStripMenuItems.

When the ContextMenuStrip is closed, set the AutoClose property back to true.

Of course, you need to perform this operation on all ToolStripDropDown components in the hierarchy, since you may want to activate this functionality to sub-items of a ToolStripMenuItem.
This action is performed by the SetMenutemsAutoClose() method.

Here, the ToolStripMenuItem that activates the ContextMenuStrip is saved to the [ContextMenuStrip].Tag property. Feel free to use any other means to store this reference.

private void anyToolStripMenuItem_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Right) {
        var menuItem = sender as ToolStripMenuItem;
        someContextMenuStrip.Tag = menuItem;
        SetMenutemsAutoClose(menuItem, false);
        someContextMenuStrip.Show(MousePosition);
        someContextMenuStrip.Capture = true;
        menuItem.BackColor = Color.FromArgb(42, SystemColors.MenuHighlight);
    }
}

private async void SomeContextMenuStrip_Closed(object sender, ToolStripDropDownClosedEventArgs e)
{
    var cms = sender as ContextMenuStrip;
    if (cms.Tag != null && cms.Tag is ToolStripMenuItem menuItem) {
        // Determine an action based on the ToolStripMenuItem
        Console.WriteLine(menuItem.Name);
        SetMenutemsAutoClose(menuItem, true);
            
        menuItem.BackColor = Color.Transparent;
        // Need to somewhat fight against the internal Timer
        await Task.Delay(100);
        if (menuItem.Owner != null) menuItem.Owner.Capture = true;
    }
}

private void SetMenutemsAutoClose(ToolStripMenuItem menu, bool autoClose)
{
    if (menu == null || menu.Owner == null) return;
    while (menu.Owner is ToolStripDropDown dropDown) {
        dropDown.AutoClose = autoClose;
        menu = dropDown.OwnerItem as ToolStripMenuItem;
    }
}

_{If Pattern Matching is not available in your version of C#, declare the variable in-line, explictly}