Question

I want to add a selector into a dictionary (the main purpose is for identifying the callback method and delegate after finish doing something)

But I find that I can not do that, the program will get an error “EXC_BAD_ACCESS”.
Are there any other way for me to add that method selector to a dictionary?
Thanks for your help.

Answer 1

Adding a new entry to a dictionary does two things (in addition to adding it to the dictionary, obviously):

1. It takes a copy of the key value. This means that the the key object must implement the NSCopying protocol
2. retains the value. This means that it needs to implement the NSObject protocol

It’s probably the second that’s causing your EXC_BAD_ACCESS.

There are at least two ways around this.

Firstly, rather than adding the selector you could add the instance of the class that implements the selector to your dictionary. Usually your class will inherit from NSObject and it will work fine. Note that it will retain the class though, maybe not what you want.

Secondly, you can convert a selector to a string (and back again) using NSSelectorFromString and NSStringFromSelector (docs are here).