単純なオブジェクトを永続化するカテゴリ ref: http://qiita.com/ykst@github/items/c5dcc71efd22e799dc31

NSObject+SimpleArchiver.h

#import <Foundation/Foundation.h>

@interface NSObject(SimpleArchiver)
// example: 
//   (archive) 
//   [SomeClass simpleArchiveForKey:@"a_key"];
//   (unarchive)
//   SomeClass *a_obj =  [SomeClass simpleUnarchiveForKey:@"a_key"];
- (BOOL)simpleArchiveForKey:(NSString *)key;
+ (id)simpleUnarchiveForKey:(NSString *)key;
@end

NSObject+SimpleArchiver.m

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

#define NSPRINTF(fmt, ...) [NSString stringWithFormat:fmt, ##__VA_ARGS__]

@implementation NSObject(SimpleArchiver)

+ (NSString *)_makeArchivePath:(Class)cls forKey:(NSString *)key
{
    // 保存場所はアプリケーションにより要調整
    NSString *plain = NSPRINTF(@"_SA_%@_%@", NSStringFromClass(cls), key);
    NSArray *document_paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                        NSUserDomainMask, YES);
    NSString *documents_path = [document_paths objectAtIndex:0];
    NSString *path = NSPRINTF(@"%@/%@", documents_path, plain);

    return path;
}

- (BOOL)simpleArchiveForKey:(NSString *)key
{
    NSString *archive_key = [NSObject _makeArchivePath:[self class] forKey:key];

    unsigned count;
    objc_property_t *properties = class_copyPropertyList([self class], &count);

    if (count == 0) return NO;

    NSMutableArray *keys = [NSMutableArray arrayWithCapacity:count];

    for (int i = 0; i < count; ++i) {
        objc_property_t property = properties[i];
        keys[i] = [NSString stringWithUTF8String:property_getName(property)];
    }

    NSDictionary *dict = [self dictionaryWithValuesForKeys:keys];

    BOOL ret = [NSKeyedArchiver archiveRootObject:dict toFile:archive_key];

    return ret;
}

+ (id)simpleUnarchiveForKey:(NSString *)key
{
    NSString *archive_key = [NSObject _makeArchivePath:[self class] forKey:key];

    NSDictionary *dict = [NSKeyedUnarchiver unarchiveObjectWithFile:archive_key];

    if (!dict) return nil;

    NSObject *obj = [[self class] new];

    [obj setValuesForKeysWithDictionary:dict];

    return obj;
}
@end