问题
I have an NSMutableString, how can I convert it to an NSString?
回答1:
Either via:
NSString *immutableString = [NSString stringWithString:yourMutableString];
or via:
NSString *immutableString = [[yourMutableString copy] autorelease];
//Note that calling [foo copy] on a mutable object of which there exists an immutable variant
//such as NSMutableString, NSMutableArray, NSMutableDictionary from the Foundation framework
//is expected to return an immutable copy. For a mutable copy call [foo mutableCopy] instead.
Being a subclass of NSString however you can just cast it to an NSString
NSString *immutableString = yourMutableString;
making it appear immutable, even though it in fact stays mutable.
Many methods actually return mutable instances despite being declared to return immutable ones.
回答2:
NSMutableString is a subclass of NSString, so you could just typecast it:
NSString *string = (NSString *)mutableString;
In this case, string would be an alias of mutalbeString, but the compiler would complain if you tried to call any mutable methods on it.
Also, you could create a new NSString with the class method:
NSString *string = [NSString stringWithString:mutableString];
来源：https://stackoverflow.com/questions/5583510/objective-c-convert-a-nsmutablestring-in-nsstring