[DropDownMenu] Controlled field should clear when value is undefined

[marnusw]

When DropDownMenu is used with a controlled SelectField the value is updated properly except when the value is undefined. In that case it should reset the select to the initial "unselected" state, but instead the last selection is maintained and displayed on top of the hint text. This is a patch to fix that. (I realise DropDownMenu will fall away eventually, but I think fixing it now is still worthwhile; this should also be outcome in any future implementation.)

I also noticed that isHovered was maintained in the DropDownMenu state which, as far as I could see, is never used. This caused a lot of unnecessary re-renders. I've removed that as well, but purposefully added it as the latter commit. If maintaining this status does serve some purpose I'm missing I'll just lop that one off.

[hai-cea]

Thanks @marnusw - looks like you did some cleanup on the hovered state as well? You may want to remove these lines?
https://github.com/marnusw/material-ui/blob/emptyControlled/src/drop-down-menu.jsx#L189

[marnusw]

Missed those, I've removed them now too.

[hai-cea]

Thanks @marnusw - after some more testing, it looks like this PR broke SelectField. Please check out #/components/text-fields on the docs site of this PR. Selecting an item blanks out the select field.

[marnusw]

The problem was on these lines. Since the SelectField doesn't have a valueMember prop, the payload object was passed up in its entirety rather than the value. Checking for a valueMember solved the issue.

However, I wonder if these three lines shouldn't be removed entirely since the same action is taken in DropDownMenu on line 284? I also can't quite figure why the changes I made broke this. I think this might have been a hidden issue all along?

(And if valueMember is specified on SelectField it will be passed down to the DropDownMenu along with the "other" props, and then it will still work as this code suggests.)

[hai-cea]

Yeh, it does seem weird that SelectField is having to handle onChange. It seems like it should be handled in one place?

[marnusw]

I've removed the change handler in SelectField completely. It is now passed through to the DropDownMenu directly.

[hai-cea]

Thanks @marnusw