Question

have no idea的用法

Answer 1

have no idea 是英语中得固定搭配。idea 是思想、观念、意见的意思，比较抽象，实际上在这个短语中，它整个词组的意思就是“不知道”，表示一点想法也没有

例句与用法：
I have no idea why he resigned his post. 我不知道他为何辞去他的职务。
I have no idea (as to) what you mean. 我一点儿也不明白你的意思。
We have no idea how to persuade him to give up the idea. 我们不知道如何说服他放弃这个念头。
I have no idea what to do. 我不知道该怎么办。
We have no idea how the birds find their way. 我们不知道这些鸟如何找到它们的路。
You have no idea how worried I was. 你想像不出来我有多么担心。

Answer 2

可以直接用作回答别人的询问，也可以后面直接加同位语从句！
eg. what are you going to do this afternoon? --------I have no idea!
I have no idea whether he will come or not.