相关疑难解决方法(0)

在iOS8和之前我可以使用:

NSString *str = ...; // some URL
NSString *result = [str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

在iOS9中stringByAddingPercentEscapesUsingEncoding已被替换为stringByAddingPercentEncodingWithAllowedCharacters:

NSString *str = ...; // some URL
NSCharacterSet *set = ???; // where to find set for NSUTF8StringEncoding?
NSString *result = [str stringByAddingPercentEncodingWithAllowedCharacters:set];

我的问题是:在哪里找到所需的NSCharacterSet(NSUTF8StringEncoding)以便正确更换stringByAddingPercentEscapesUsingEncoding？