Runtime & 一键序列化

原理描述：

用runtime提供的函数遍历Model自身全部属性，并对属性进行encode和decode操做。

核心方法：在Model的基类中重写方法：

- (id)initWithCoder:(NSCoder *)aDecoder {
    if (self = [super init]) {
        unsigned int outCount;
        Ivar * ivars = class_copyIvarList([self class], &outCount);
        for (int i = 0; i < outCount; i ++) {
            Ivar ivar = ivars[i];
            NSString * key = [NSString stringWithUTF8String:ivar_getName(ivar)];
            [self setValue:[aDecoder decodeObjectForKey:key] forKey:key];
        }
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder {
    unsigned int outCount;
    Ivar * ivars = class_copyIvarList([self class], &outCount);
    for (int i = 0; i < outCount; i ++) {
        Ivar ivar = ivars[i];
        NSString * key = [NSString stringWithUTF8String:ivar_getName(ivar)];
        [aCoder encodeObject:[self valueForKey:key] forKey:key];
    }
}