doing 在这个句子中作什么成分？ 为什么用doing?

If you become rich, you will have a difficult time (in) knowing who your real friends are.
=If you become rich, you will have difficulty( in) knowing who your real friends are.
have difficulty( in) doing=have a difficult time (in) doing
固定搭配，省掉了in,介词后跟动名词。

作结果状语，经历困难，（最后）知道谁是真正的朋友
doing表示主动，因为是“你”知道，you know本回答被网友采纳

doing 在此句子中 是固定搭配的结果 本句子有固定搭配 have a difficult time doing sth 希望能帮到你

状语。固定搭配have a （形容词） time doing sth

同位语，解释time
另有have a difficuly (in) doing sth.的用法。