Problem description

In my case, I need to implement focus the form control programmably. So I need to access the components via ref. Things has done except the SelectField component.
SelectField is composed by TextField and DropDownMenu, and I notice that I can not access the DropDownMenu because there is no ref attribute.

I wonder why you guys do not add a ref attribute in the DropDownMenu component in SelectField ?

I can send a pull request if you need.