Objective-C Runtime in Practice: Mapping Dictionaries to Models

English translation of the Chinese original, translated on 2026-10-23. The article body uses automated translation; app descriptions, historical reading notes and video subtitles receive separate editorial checks. Original publication dates, attribution, code and version notes are retained.

It has been a while since my last article because our company project has been busy. Here is a beginner’s evolution—come and see 😄. When I was starting out, I dutifully wrote the following code in models to convert dictionaries:

1. Manual parsing

//手动解析
 - (instancetype)initWithDic
{
    self = [super init];
    if (self) {
        xxx = dic[@"xxx"];
        ...
    }
    return self;
}

2. KVC parsing

//kvc解析
 - (instancetype)initWithDic
{
    self = [super init];
    if (self) {
        [self setValuesForKeysWithDictionary:dict];
    }
    return self;
}

3. Third-party frameworks

Does this look familiar? Everyone evolves when learning iOS. I wrote this way until leaving that company and being thoroughly challenged in interviews elsewhere by sophisticated low-level questions. Interviews can help us grow: seeing gaps forces us to improve. I hope that reflection helps. Now to the subject.

I generally use KVC for parsing, sometimes with third-party frameworks such as MJ's MJExtension or JsonModel. I hear RunTime has become a popular interview topic. To be honest, my low-level knowledge is weak because I rarely use it in actual projects and forget it after a while. Plenty of material is already online, but I will join in too. 😄 Here is some practical work from studying RunTime.

1. First, create an NSObject category named DicToModel.

2. Add a dictionary-to-model method named:


+ (instancetype)createModelWithDict:(NSDictionary *)dict;

3. Import the runtime header: #import <objc/message.h>.

4. Implement the methods declared in the .h file.

+ (instancetype)createModelWithDict:(NSDictionary *)dict{
    
    // 1.创建对应类的对象
    id model = [[self alloc] init];
    
    // runtime:遍历模型中所有成员属性,去字典中查找
    // 属性定义在哪,定义在类,类里面有个属性列表(数组)
    
    // 遍历模型所有成员属性
    // ivar:成员属性
    // class_copyIvarList:把成员属性列表复制一份给你
    // Ivar *:指向Ivar指针
    // Ivar *:指向一个成员变量数组
    // class:获取哪个类的成员属性列表
    // count:成员属性总数
    unsigned int count = 0;
    Ivar *ivarList = class_copyIvarList([self class], &count);
    for (int i = 0 ; i < count; i++) {
        // 获取成员属性
        Ivar ivar = ivarList[i];
        
        // 获取成员名
        NSString *propertyName = [NSString stringWithUTF8String:ivar_getName(ivar)];
        // 获取key
        NSString *key = [propertyName substringFromIndex:1];
        
        // user value:字典
        // 获取字典的value
        id value = dict[key];
        // 给模型的属性赋值
        // value:字典的值
        // key:属性名
        
        // 成员属性类型
        NSString *propertyType = [NSString stringWithUTF8String:ivar_getTypeEncoding(ivar)];
        // 二级转换
        // 值是字典,成员属性的类型不是字典,才需要转换成模型
        if ([value isKindOfClass:[NSDictionary class]] && ![propertyType containsString:@"NSDictionary"]) { // 需要字典转换成模型
            // @"@\"xxxx\"" 截取类名字符串
            NSRange range = [propertyType rangeOfString:@"\""];
            propertyType = [propertyType substringFromIndex:range.location + range.length];
            // xxxx\"";
            range = [propertyType rangeOfString:@"\""];
            propertyType = [propertyType substringToIndex:range.location];
            // 获取需要转换类的类对象
            Class modelClass =  NSClassFromString(propertyType);
            
            if (modelClass) {
                value =  [modelClass createModelWithDict:value];
            }
        }
        if (value) {// KVC赋值:不能传空
            [model setValue:value forKey:key];
            
        }
        
    }
    
    
    return model;
}

The code above implements two-level dictionary-to-model conversion and generally works for ordinary cases. To support other cases, add value isKindOfClass checks and the corresponding handling. See the comments for details. Next, here is how to call it:

- (void)viewDidLoad {
    [super viewDidLoad];
    // 解析Plist
    NSString *filePath = [[NSBundle mainBundle] pathForResource:@"status.plist" ofType:nil];
    NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:filePath];
    NSArray *dictArr = dict[@"statuses"];
    NSMutableArray *statusesData = [NSMutableArray array];
    // 遍历字典数组
    for (NSDictionary *dict in dictArr) {
        //传字典给我们写的分类返回一个status的模型
        Status *status = [Status createModelWithDict:dict];
        [statusesData addObject:status];
    }
    NSLog(@"%@",statusesData);
}