How can I get the index of sub UIView in the parent view?

I want to use exchangeSubviewAtIndex: withSubviewAtIndex: method.

but how can i get the indexes of those views? i already have their pointers, so I thought there might be a method like.

[parentView indexOfSubview:subview];

but I couldn't find that kind of thing in Xcode documents library.

please help me! thank you in advance.