Case-insensitive KVC in Cocoa? [closed] - cocoa

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I'd appreciate some feedback on a particular approach I'm thinking of using. The scenario is below.
I have an object (lets call it MObject) that has a number of properties, say, x and y coordinates, height and width. The properties are named according to the KVC guidelines (MObject.x; MObject.height, etc). My next task, is to read in an XML file that describes this MObject. Unfortunately, the XML elements are named differently -- X and Y, Height and Width (note the capitalization).
Ideally, the XML elements would match up with MObject's properties. In this case, I could use KVC and avoid a whole whack of code:
for (xmlProperty in xmlElement)
{
[MObject setValue:xmlProperty.value forKey:xmlProperty.name].
}
One way of approaching this would be to make use of case-insensitive keys. Where would I start with that? Are there any other, better solutions?
Suggestions very much appreciated.

Answer 1

Don't override -[NSObject valueForKey:] and -[NSObject setValue:forKey:] if you can at all help it.
Your best bet would be to convert the keys you get from the XML file on the fly. Use a separate method to do the conversion and you can also maintain a cache of names to property keys, so you only need to do each conversion once.
- (NSString *)keyForName:(NSString *)name {
// _nameToKeyCache is an NSMutableDictionary that caches the key
// generated for a given name so it's only generated once per name
NSString *key = [_nameToKeyCache objectForKey:name];
if (key == nil) {
// ...generate key...
[_nameToKeyCache setObject:key forKey:name];
}
return key;
}
- (void)foo:xmlElement {
for (xmlProperty in xmlElement) {
[myObject setValue:xmlProperty.value forKey:[self keyForName:xmlProperty.name]].
}
}

Answer 2

You can use NSString's lowercaseString to convert the XML key name to lowercase, if that helps.

Answer 3

Override -valueForUndefinedKey: and -setValue:forUndefinedKey:
If you find a key with a different capitalization use it, otherwise call up to super.

Answer 4

Override -valueForKey: and -setValue:forKey:.
You should probably only accept keys (element/attribute names) you recognize, and call up to super for other keys.

Answer 5

So I implemented Chris Hanson's suggestion and here's what I ended up with. I put this in my Utils class. It keeps a dictionary for each class that we lookup. It could probably use a little refactoring but it has worked very well for me so far.
static NSMutableDictionary *keyCache;
+ (NSString *)keyForClass:(Class)klass column:(NSString *)column {
if (!keyCache) { keyCache = [NSMutableDictionary dictionary]; }
NSString *className = NSStringFromClass(klass);
NSMutableDictionary *tableKeyCache = [keyCache objectForKey:className];
if (!tableKeyCache) {
tableKeyCache = [NSMutableDictionary dictionary];
unsigned int numMethods = 0;
Method *methods = class_copyMethodList(klass, &numMethods);
NSMutableArray * selectors = [NSMutableArray array];
for (int i = 0; i < numMethods; ++i) {
SEL selector = method_getName(methods[i]);
[selectors addObject:NSStringFromSelector(selector)];
}
[tableKeyCache setValue:selectors forKey:#"allSelectors"];
free(methods);
[keyCache setValue:tableKeyCache forKey:className];
}
NSString *keyToReturn = [tableKeyCache valueForKey:column];
if (!keyToReturn) {
for (NSString *columnKey in [tableKeyCache valueForKey:#"allSelectors"]) {
if ( [column caseInsensitiveCompare:columnKey] == NSOrderedSame) {
[tableKeyCache setValue:columnKey forKey:column];
keyToReturn = columnKey;
break;
}
}
}
if (!keyToReturn) { // Taking a guess here...
NSLog(#"Selector not found for %#: %# ", className, column);
keyToReturn = [Utils keyForClass:[klass superclass] column:column];
}
return keyToReturn;
}