VMJsonableObject helps developer to easily fill an NSObject with NSDictionary (probably parsed from a JSON string).

VMJsonableObject

// For example, let's define a VMUser class that saves user login info.

// VMUser.h
@interface VMUser : VMJsonableObject

@property (nonatomic)NSString *userId;
@property (nonatomic)NSString *userName;
@property (nonatomic)NSString *email;

@end

// VMUser.m
// Note the implementation part of `VMUser.m` file is empty.
// You only needs to write logic-related code now. YAY.
@implementation VMUser

@end

// And in the method you want to use it
id object = [NSJSONSerialization
                JSONObjectWithData:serverResponseData
                options:0
                error:nil];
if([object isKindOfClass:[NSDictionary class]]) {
    NSDictionary *results = (NSDictionary *)object;
    VMUser *user = [[VMUser alloc] initWithDictionary:results];
    NSLog(@"Login: %@", user.userName);
}

VMJsonableObject.h

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

@interface VMJsonableObject : NSObject

- (id)initWithDictionary:(NSDictionary *)dictionary;

@end

VMJsonableObject.m

#import "VMJsonableObject.h"

@implementation VMJsonableObject

- (id)initWithDictionary:(NSDictionary *)dictionary
{
    if (self = [super init]) {
        [self fillValues:dictionary];
    }

    return self;
}

// This is problem oriented method. Please change to match your own situation.
// In my case, the API property is `user_id` while the property name is `userId`
// If your json property name is exactly as your property name, simply return it.
// Otherwise, do whatever it takes to make them match.
- (NSString *)convertToJSONName:(NSString *)propertyName
{
    // Step 1: find all (unique) uppercase characters
    NSArray *occurrences = [propertyName componentsSeparatedByCharactersInSet:[[NSCharacterSet uppercaseLetterCharacterSet] invertedSet]];
    NSSet *uniqueUppercaseCharacters = [NSSet setWithArray:occurrences];

    // Step 2: replace the uppercase letters with format of `_[lowercase]`
    for (NSString *uppercaseCharacter in uniqueUppercaseCharacters) {
        propertyName = [propertyName stringByReplacingOccurrencesOfString:uppercaseCharacter
                                                               withString:[NSString stringWithFormat:@"_%@", [uppercaseCharacter lowercaseString]]];
    }
    return propertyName;
}

// Fill object with parsed dictionary from JSON string.
// This method uses runtime support provided by Objective-C.
// The advantage is quite obvious. It literally makes the function smaller.
- (void)fillValues:(NSDictionary *)dictionary
{
    NSString *className = NSStringFromClass([self class]);
    id curClass = objc_getClass([className UTF8String]);
    unsigned int outCount, i;
    objc_property_t *properties = class_copyPropertyList(curClass, &outCount);
    for (i = 0; i < outCount; i++) {
        objc_property_t property = properties[i];
        NSString *propertyName = [NSString stringWithCString:property_getName(property) encoding:NSUTF8StringEncoding];
        id value = [dictionary objectForKey:[self convertToJSONName:propertyName]];
        if (value) {
            [self setValue:value forKey:propertyName];
        }
    }
}

@end

Why?

It is a (more than) common situation for developers to parse some JSON strings returned by a server and fill NSObject instances with the parsed NSDictionary objects.

A "simply" yet very tedious way is to call the set method for every property you got in the init method, probably like the following:

self.userId = [dictionary objectForKey: @"user_id"];
self.userName = [dictionary objectForKey: @"user_name"];
self.age = [dictionary objectForKey: @"age"];
// and the list goes on...

Well that's working, but not so elegant. Why not turn to runtime support for help. That's what VMJsonableObject does. It helps you, as developer, to fill in data with NSDictonary object you passed in to initializer.

You can simply create a class extending VMJsonableObject, and add whatever property you want to (to make your life even easier, I recommend JSONtoFoundation for you). And boom, it's just working.

Advantages

• Less code means less change to make mistakes
• Very DRY
• Easy to change

Disadvantages

• Precious SUPERCLASS

f**king cool!!!