what about后面加动原还是动名词?我听说加动名词,应为介词后加动名词.见下!

what about后面应加动名词.即:
What/How about doing sth.你认为做某事如何?(用来征求对方的意见)
这是一个固定结构,不需要谓动的.
其实它是一个省略句.补充完整为:
What/How do you think about doing sth.
如:What/How about going for a walk after suppe