Is it possible to use a wildcard in KVC?

Question

I\'m trying to use wildcard in KVC like this.

Is it possible?

Or Is there other ways to use a wildcard to indicate a member variable?

@interface          


        

Answer 1

I'll raise your wildcards by adding Regex, and by using categories:

To read about how regex works with this, please read the NSRegularExpression Class Reference.

Features:

• Uses regex, for matching of a wide variety of keys
• Uses a category that works on any instance
• Caches key lists per class
• Full KVC support (not just properties, but accessor methods & iVars too!)
• Integrates flawlessly with current KVC methods (only uses the regex if the key wasn't found, improving performance)
• Subclassing doesn't mess it up, like @JamesWebster's solution
• Doesn't needlessly pollute the list of keys with NSObject's methods
• Returns a NSDictionary of matched keys & values

Cons:

• Uses regex, which is slower and more complex to understand
• Slow initial lookup for a class (must iterate through all methods & iVars)
• Automatically overwrites the -valueForUndefinedKey: method, so it's possible that this could break some existing code (move it to it's own method to fix).
• Currently doesn't support setting of values (by design, that's a whole other bag of cats).
• Can have duplicate keyPaths in the result (not the biggest of issues, but stems from the fact that KVC matching is complex, and I have to implement all of the rules)
• Uses NSRegularExpression, which is only available in iOS 4 and later (not the largest of issues).

Version History:

• 1.0: Initial Release

So, here is the code:

NSObject+KVCRegex.h:

//
//  NSObject+KVCRegex.h
//  TestProj
//
//  Created by Richard Ross on 8/20/12.
//  Copyright (c) 2012 Ultimate Computer Services, Inc. All rights reserved.
//

#import 

@interface NSObject (KVCRegex)

// custom implemenation
-(id) valueForUndefinedKey:(NSString *)key;

@end

NSObject+KVCRegex.m:

//
//  NSObject+KVCRegex.m
//  TestProj
//
//  Created by Richard Ross on 8/20/12.
//  Copyright (c) 2012 Ultimate Computer Services, Inc. All rights reserved.
//

#import "NSObject+KVCRegex.h"
#import 

@implementation NSObject (KVCRegex)

static NSSet *keyPathsForClass(Class cls)
{
    NSMutableSet *keys = [NSMutableSet set];

    do
    {
        if (cls == [NSObject class])
        {
            // nothing good can come from trying to use KVC on NSObject methods
            break;
        }

        unsigned count = 0;
        Method *methods = class_copyMethodList(cls, &count);

        for (int i = 0; i < count; i++) {
            // make sure that the method returns a value
            const char *methodName = sel_getName(method_getName(methods[i]));

            char returnType[64];
            method_getReturnType(methods[i], returnType, 64);
            if (strcmp(returnType, "v") == 0)
                continue;

            // make sure that the method takes no args (except for self & _cmd)
            if (method_getNumberOfArguments(methods[i]) == 2)
            {
                // add a duplicate entry for ones matching 'is'
                if (strstr(methodName, "is") == methodName)
                {
                    char *newStr = strdup(methodName + 2);
                    newStr[0] = tolower(newStr[0]);

                    [keys addObject:[NSString stringWithUTF8String:newStr]];

                    free(newStr);
                }

                [keys addObject:[NSString stringWithUTF8String:methodName]];
            }
        }

        free(methods);

        // now copy iVars

        count = 0;
        Ivar *ivars = class_copyIvarList(cls, &count);
        for (int i = 0; i < count; i++)
        {
            const char *ivarName = ivar_getName(ivars[i]);

            if (strstr(ivarName, "_") == ivarName)
                [keys addObject:[NSString stringWithUTF8String:ivarName + 1]]; // iVar name starting with _

            [keys addObject:[NSString stringWithUTF8String:ivarName]];
        }

        free(ivars);
    } while ((cls = [cls superclass]));

    return [NSSet setWithSet:keys];
}

// returns a dictionary based on 'key' as a regex
-(id) valueForUndefinedKey:(NSString *)key
{
    // lookup for later use
    static NSMutableDictionary *keyClassPairs;
    if (!keyClassPairs)
        keyClassPairs = [NSMutableDictionary dictionary];

    if (!keyClassPairs[[self class]])
    {
        keyClassPairs[(id)[self class]] = keyPathsForClass([self class]);
    }

    NSSet *keyPaths = keyClassPairs[[self class]];

    // assume 'key' is a regex
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:key options:0 error:nil];
    NSMutableArray *matches = [NSMutableArray array];

    for (NSString *keyPath in keyPaths)
    {
        NSRange matchRange = [regex rangeOfFirstMatchInString:keyPath options:0 range:(NSRange) { 0, keyPath.length }];

        if (matchRange.length == keyPath.length)
        {
            // we have a match
            [matches addObject:keyPath];
        }
    }

    if (matches.count)
        return [self dictionaryWithValuesForKeys:matches];
    else
        [NSException raise:NSUndefinedKeyException format:@"Could not find a key that matches the regex in %@", key];

    return nil;
}

@end

Example:

@interface MyObject : NSObject
{
@public
    int normalIvar;
    id _underscoreIvar;
}

@property id     someProp;
@property BOOL isProperty;
@property int  nativeProp;

-(void) notAKey;
-(id) aKey;

@end

@implementation MyObject

@synthesize someProp, isProperty, nativeProp;

-(void) notAKey
{
    NSLog(@"Not a key!");
}

-(id) aKey
{
    return @"Value";
}

@end

int main()
{
    @autoreleasepool {
        MyObject *obj = [MyObject new];

        obj.someProp = @"a property";
        obj.nativeProp = 15;
        obj.isProperty = YES;
        obj->normalIvar = 172;
        obj->_underscoreIvar = @"Ivar";

        NSString *regex = @"[a|s].*"; // match a key starting with 'a' or 's', then matching anything else after

        NSLog(@"%@", [obj valueForKey:regex]); // prints "{ aKey = 'Value', someProp = 'a property' }"

        regex = @"_.*"; // match a key starting with '_', and then match anything else after

        NSLog(@"%@", [obj valueForKey:regex]); // prints "{ _underscoreIvar = 'Ivar' }"

        regex = @".*"; // match any key declared for this object

        NSLog(@"%@", [obj valueForKey:regex]); // prints "{ "_underscoreIvar" = Ivar; aKey = Value; isProperty = 1; nativeProp = 15; normalIvar = 172; property = 1; someProp = "a property"; underscoreIvar = Ivar; }"

        regex = @"(?i)[A-J].*"; // match (case insensitive) a key starting with A - J

        NSLog(@"%@", [obj valueForKey:regex]); // prints "{ aKey = value; isProperty = 1; }"
    }
}