问题
I am trying to convert a piece of Java code which uses a HashMap that contains as a key an object and a value as an object.
private static HashMap<Class<? extends Component>, ComponentType> componentTypes = new HashMap<Class<? extends Component>, ComponentType>();
I've been reading on how to do this with Obj-C but I have not been successful, most people suggest using a NSDictionary, the problem is that they keys need to be strings and I need them as objects. The other option was NSMapTable, however it is not available on iOS. Would someone be able to assist on how I can convert this into an obj-c equivalent?
thanks,
回答1:
The keys for an NSDictionary do not need to be strings. They can be any object that implements NSCopying. If the object is a custom object, however, it needs to produce sane responses to the -hash and -isEqual: messages, but this is the same as using an object in a Java collection so it shouldn't be much of a challenge.
回答2:
An NSMutableDictionary (assuming that you also need to set values in the dictionary after its initialization) works in two ways:
As a traditional dictionary/hashmap in which you set values like this:
[myDictionary setObject: theValue forKey: anyObject];As an object with KVC-compliant properties that happen to be defined dynamically:
[myDictionary setValue: theValue forKey: aString];
If the key is an NSString, then the two are interchangeable, with the exception that you can't set an object to nil with setObject:forKey:, but you can pass nil to setValue:forKey:.
回答3:
You want to use an NSDictionary. You say that
they keys need to be strings and I need them as objects
The keys to an NSDictionary don't need to be strings -- they can be any object that conforms to the NSCopying protocol.
回答4:
From NSDictionary reference
A key-value pair within a dictionary is called an entry. Each entry consists of one object that represents the key and a second object that is that key’s value. Within a dictionary, the keys are unique. That is, no two keys in a single dictionary are equal (as determined by isEqual:). In general, a key can be any object (provided that it conforms to the NSCopying protocol—see below), but note that when using key-value coding the key must be a string (see “Key-Value Coding Fundamentals”). Neither a key nor a value can be nil; if you need to represent a null value in a dictionary, you should use NSNull.
So any object that meets the NSCopying protocol can be used as a key. The string restriction is only for Key-Value Coding used for Cocoa bindings
回答5:
I'm inferring that you are using a key that is does not conform to the NSCopying Protocol. In that case try using the Core Foundation equivalent of NSDictionary: CFDictionary.
http://developer.apple.com/library/ios/#documentation/CoreFoundation/Reference/CFDictionaryRef/Reference/reference.html
Just make sure that when you are using CFDictionary that all of your objects are going to be retained in memory for the duration of the object. Since CFDictionary has to be set with weak references (at least in my experience) just be careful that you don't accidentally dealloc one of your objects whiles it's still in the CFDictionary.
While CFDictionary is “toll-free bridged” with its Cocoa Foundation counterpart, NSDictionary, I find that there are still problems with this. I've tried to add objects that were not part of the NSCopying protocol to my toll-free bridged NSDictionary and it came up with an error at run time.
CFDictionary docs: http://developer.apple.com/library/ios/#documentation/CoreFoundation/Reference/CFDictionaryRef/Reference/reference.html
If you need mutability, use CFMutableDictionary instead like so: cfd = CFDictionaryCreateMutable(NULL, 0, NULL, NULL); CFDictionaryAddValue(cfd, key, value); CFRelease(cfd);
CFMutableDictionary docs: http://developer.apple.com/library/ios/#documentation/CoreFoundation/Reference/CFMutableDictionaryRef/Reference/reference.html#//apple_ref/doc/uid/20001497
来源：https://stackoverflow.com/questions/8670681/objective-c-hashmap-equivalent