Button inside a MenuItem won't open Sub-MenuItems

Question

I have a Button inside a MenuItem.Header like this:

<Menu>
    <MenuItem>
        <MenuItem.Header>
            <Button>Hello</Button>
        </MenuItem.Header>
        <MenuItem Header="SubItem1"/>
        <MenuItem Header="SubItem2"/>
    </MenuItem>
</Menu>

if I click the MenuItem outside the Button, the sub-menu opens. But if I click the Button the sub-menu will not open. I believe that's because the event of the clicked is not passed to the MenuItem. How do I fix it?

In short - I want the sub-menu to open when clicking the Button.

(The use is mainly for styling purposes, I have a button style and I want to use it as a MenuItem)

Answer 1

A Button doesn't know how to expand a MenuItem unless you tell it how to by writing some code:

<Menu>
    <MenuItem>
        <MenuItem.Header>
            <Button Click="Button_Click">Hello</Button>
        </MenuItem.Header>
        <MenuItem Header="SubItem1"/>
        <MenuItem Header="SubItem2"/>
    </MenuItem>
</Menu>

---

private void Button_Click(object sender, RoutedEventArgs e)
{
    Button btn = (Button)sender;
    MenuItem mi = btn.Parent as MenuItem;
    if (mi != null)
        mi.IsSubmenuOpen = !mi.IsSubmenuOpen;
}