Property list serialization protocol/category. This allows you to easily make an NSObject subclass generate a plist version of itself, or initialize itself from a plist. Simply conform to the TsPropertyListRepresentation protocol and call the +includeKeyInPropertyListRepresentation:... methods at an appropriate time, such as an +initialize metho…

NSObject+TsPropertyListRepresentation.h

//
//  NSObject+TsPropertyListRepresentation.h
//  PressKit
//
//  Created by Brent Royal-Gordon on 3/6/13.
//  Copyright (c) 2013 Novelty Publishers. All rights reserved.
//

#import <Foundation/Foundation.h>

@protocol TsPropertyListRepresentation <NSObject>

// These all automatically become available to NSObject subclasses which conform to this protocol.
@optional

- (id)initWithPropertyListRepresentation:(NSDictionary*)rep;
@property (readonly) NSDictionary* propertyListRepresentation;

- (instancetype)willInitWithPropertyListRepresentation:(NSDictionary*)rep;
- (instancetype)didInitWithPropertyListRepresentation:(NSDictionary*)rep;

// Call these from a +initialize method
+ (void)includeKeyInPropertyListRepresentation:(NSString*)key;
+ (void)includeKeyInPropertyListRepresentation:(NSString*)key withValueTransformer:(NSValueTransformer*)transformer;
+ (void)includeKeyInPropertyListRepresentation:(NSString*)key withValueTransformer:(NSValueTransformer*)transformer propertyListKey:(NSString*)plistKey;

@end

NSObject+TsPropertyListRepresentation.m

//
//  NSObject+TsPropertyListRepresentation.m
//  PressKit
//
//  Created by Brent Royal-Gordon on 3/6/13.
//  Copyright (c) 2013 Novelty Publishers. All rights reserved.
//

#import "NSObject+TsPropertyListRepresentation.h"
#import <objc/runtime.h>

@interface TsNoOpValueTransformer : NSValueTransformer @end

@implementation NSObject (TsPropertyListRepresentation)

+ (NSMutableDictionary*)ts_propertyListRepresentationKeysForThisClassOnly {
    NSMutableDictionary * dict = objc_getAssociatedObject(self, _cmd);
    if(!dict) {
        dict = [NSMutableDictionary new];
        objc_setAssociatedObject(self, _cmd, dict, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return dict;
}

+ (NSDictionary*)ts_propertyListRepresentationKeys {
    NSMutableDictionary * dict = ([self.superclass ts_propertyListRepresentationKeys] ?: @{}).mutableCopy;
    [dict addEntriesFromDictionary:[self ts_propertyListRepresentationKeysForThisClassOnly]];
    return dict;
}

+ (void)includeKeyInPropertyListRepresentation:(NSString*)key withValueTransformer:(NSValueTransformer*)transformer propertyListKey:(NSString *)plistKey {
    if(![self conformsToProtocol:@protocol(TsPropertyListRepresentation)]) {
        [self doesNotRecognizeSelector:_cmd];
    }
    
    [self ts_propertyListRepresentationKeysForThisClassOnly][key] = @{ @"plistKey": plistKey, NSValueTransformerBindingOption: transformer ?: [TsNoOpValueTransformer new] };
}

+ (void)includeKeyInPropertyListRepresentation:(NSString*)key withValueTransformer:(NSValueTransformer *)transformer {
    [self includeKeyInPropertyListRepresentation:key withValueTransformer:transformer propertyListKey:key];
}

+ (void)includeKeyInPropertyListRepresentation:(NSString*)key {
    [self includeKeyInPropertyListRepresentation:key withValueTransformer:nil];
}

- (id)initWithPropertyListRepresentation:(NSDictionary*)plist {
    if(![self conformsToProtocol:@protocol(TsPropertyListRepresentation)]) {
        [self doesNotRecognizeSelector:_cmd];
        return nil;
    }
    
    if((self = [self init])) {
        self = [self willInitWithPropertyListRepresentation:plist];
        
        for(NSString * key in [self.class ts_propertyListRepresentationKeys]) {
            NSDictionary * info = [self.class ts_propertyListRepresentationKeys][key];
            
            id value = plist[info[@"plistKey"]];
            if(!value) {
                continue;
            }
            value = [info[NSValueTransformerBindingOption] reverseTransformedValue:value];
            
            [self setValue:value forKey:key];
        }
        
        self = [self didInitWithPropertyListRepresentation:plist];
    }
    
    return self;
}

- (instancetype)willInitWithPropertyListRepresentation:(NSDictionary*)rep { return self; }
- (instancetype)didInitWithPropertyListRepresentation:(NSDictionary*)rep { return self; }

- (NSDictionary*)propertyListRepresentation {
    if(![self conformsToProtocol:@protocol(TsPropertyListRepresentation)]) {
        [self doesNotRecognizeSelector:_cmd];
        return nil;
    }
    
    NSMutableDictionary * plist = [NSMutableDictionary new];
    for(NSString * key in [self.class ts_propertyListRepresentationKeys]) {
        NSDictionary * info = [self.class ts_propertyListRepresentationKeys][key];
        
        id value = [self valueForKey:key];
        value = [info[NSValueTransformerBindingOption] transformedValue:value];
        if(!value) {
            continue;
        }
        
        plist[info[@"plistKey"]] = value;
    }
    
    return plist.copy;
}

@end

@implementation TsNoOpValueTransformer

+ (BOOL)allowsReverseTransformation {
    return YES;
}

- (id)transformedValue:(id)value {
    return value;
}

@end