IOS笔记：撸一个 JSON->Model 之 YYMo

YYModel 源码阅读笔记:
首先调用

1. + (instancetype)modelWithJSON:(id)json;

+ (instancetype)modelWithJSON:(id)json {
    //将传进来的源数据转成NSDictionary类型，
    //支持NSString，NSData，NSDictionary
    NSDictionary *dic = [self _yy_dictionaryWithJSON:json];
    // jsos->model
    return [self modelWithDictionary:dic];
}

2. + (NSDictionary *)_yy_dictionaryWithJSON:(id)json;

//转换成NSDictionary
+ (NSDictionary *)_yy_dictionaryWithJSON:(id)json {
    //json非空判断 (kCFNull为NSNULL的单例)
    if (!json || json == (id)kCFNull) return nil;
    NSDictionary *dic = nil;
    NSData *jsonData = nil;
    //如果是字典类型直接返回
    if ([json isKindOfClass:[NSDictionary class]]) {
        dic = json;
    } else if ([json isKindOfClass:[NSString class]]) { //如果是字符串类型，转成NSData类型
        jsonData = [(NSString *)json dataUsingEncoding : NSUTF8StringEncoding];
    } else if ([json isKindOfClass:[NSData class]]) {   //如果是data，直接赋值
        jsonData = json;
    }
    if (jsonData) { //将data类型的数据转换成NSDictionary
        dic = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:NULL];
        if (![dic isKindOfClass:[NSDictionary class]]) dic = nil;
    }
    return dic;
}

3.- (BOOL)modelSetWithDictionary:(NSDictionary *)dic;

- (BOOL)modelSetWithDictionary:(NSDictionary *)dic {
    if (!dic || dic == (id)kCFNull) return NO;  //非空的检查
    if (![dic isKindOfClass:[NSDictionary class]]) return NO;   //类型的检查
    
    //获取元类model
    _YYModelMeta *modelMeta = [_YYModelMeta metaWithClass:object_getClass(self)];
    // 没有key->property直接返回
    if (modelMeta->_keyMappedCount == 0) return NO;
    
    // 如果重写了此方法，可修改数据源
    if (modelMeta->_hasCustomWillTransformFromDictionary) {
        dic = [((id<YYModel>)self) modelCustomWillTransformFromDictionary:dic];
        if (![dic isKindOfClass:[NSDictionary class]]) return NO;
    }
    //结构体
    ModelSetContext context = {0};
    //model的元数据
    context.modelMeta = (__bridge void *)(modelMeta);
    //model本身
    context.model = (__bridge void *)(self);
    //model 数据源
    context.dictionary = (__bridge void *)(dic);
    
    //CFDictionaryApplyFunction / CFArrayApplyFunction
    //会为 dictionary / array 数据中指定范围的每一个元素调用一次指定的方法
    //遍历容器类能带来性能提升
    //元类model的property个数小于数据源个数
    if (modelMeta->_keyMappedCount >= CFDictionaryGetCount((CFDictionaryRef)dic)) {
        //基本的json->model : 类似 @{@"name":@"henry"};
        CFDictionaryApplyFunction((CFDictionaryRef)dic, ModelSetWithDictionaryFunction, &context);
        //如果重写了 modelCustomPropertyMapper 方法，才会有可能调用下面两个方法
        if (modelMeta->_keyPathPropertyMetas) {
            /**
            + (NSDictionary *)modelCustomPropertyMapper {
                return @{@"name"  : @"n",
                         @"page"  : @"p",
                         @"desc"  : @"ext.desc",
                         @"bookID": @[@"id", @"ID", @"book_id"]};
            }
             */
            //此方法支持的类型  @{@"desc"  : @"ext.desc"}
            CFArrayApplyFunction((CFArrayRef)modelMeta->_keyPathPropertyMetas,
                                 CFRangeMake(0, CFArrayGetCount((CFArrayRef)modelMeta->_keyPathPropertyMetas)),
                                 ModelSetWithPropertyMetaArrayFunction,
                                 &context);
        }
        //此方法支持的类型  @{@"bookID": @[@"id", @"ID", @"book_id"]}
        if (modelMeta->_multiKeysPropertyMetas) {
            CFArrayApplyFunction((CFArrayRef)modelMeta->_multiKeysPropertyMetas,
                                 CFRangeMake(0, CFArrayGetCount((CFArrayRef)modelMeta->_multiKeysPropertyMetas)),
                                 ModelSetWithPropertyMetaArrayFunction,
                                 &context);
        }
    } else {
        //解析全部property
        CFArrayApplyFunction((CFArrayRef)modelMeta->_allPropertyMetas,
                             CFRangeMake(0, modelMeta->_keyMappedCount),
                             ModelSetWithPropertyMetaArrayFunction,
                             &context);
    }
    //检查是否存在此方法，(此方法为默认转换不符合调用的模型对象)
    if (modelMeta->_hasCustomTransformFromDictionary) {
        return [((id<YYModel>)self) modelCustomTransformFromDictionary:dic];
    }
    return YES;
}

3.1 [_YYModelMeta metaWithClass:object_getClass(self)]; 初始化方法

/// Returns the cached model class meta
+ (instancetype)metaWithClass:(Class)cls {
    if (!cls) return nil;
    static CFMutableDictionaryRef cache;
    static dispatch_once_t onceToken;
    static dispatch_semaphore_t lock;
    dispatch_once(&onceToken, ^{
        cache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
        //创建信号量，只有一个线程访问资源
        lock = dispatch_semaphore_create(1);
    });
    //将信号量的值 -1
    dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
    _YYModelMeta *meta = CFDictionaryGetValue(cache, (__bridge const void *)(cls));
    //将信号量的值 +1
    dispatch_semaphore_signal(lock);
    if (!meta || meta->_classInfo.needUpdate) {
        meta = [[_YYModelMeta alloc] initWithClass:cls];
        if (meta) {
            dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
            CFDictionarySetValue(cache, (__bridge const void *)(cls), (__bridge const void *)(meta));
            dispatch_semaphore_signal(lock);
        }
    }
    return meta;
}

3.2 ModelSetWithDictionaryFunction 基础的dictionary转model

static void ModelSetWithDictionaryFunction(const void *_key, const void *_value, void *_context) {
    //获取当前context结构体
    ModelSetContext *context = _context;
    //context model的元数据
    __unsafe_unretained _YYModelMeta *meta = (__bridge _YYModelMeta *)(context->modelMeta);
    //元数据的源数据 dictionary
    __unsafe_unretained _YYModelPropertyMeta *propertyMeta = [meta->_mapper objectForKey:(__bridge id)(_key)];
    //context model(调用者)
    __unsafe_unretained id model = (__bridge id)(context->model);
    while (propertyMeta) {
        //获取到元类型 set方法，给model(调用者)每一个property赋值
        if (propertyMeta->_setter) {
            ModelSetValueForProperty(model, (__bridge __unsafe_unretained id)_value, propertyMeta);
        }
        //递归调用，如果下一个meta有多个属性，如果为nil则跳出while循环
        propertyMeta = propertyMeta->_next;
    };
}

3.3 ModelSetWithPropertyMetaArrayFunction 复杂的模式转model

static void ModelSetWithPropertyMetaArrayFunction(const void *_propertyMeta, void *_context) {
    //获取当前context结构体
    ModelSetContext *context = _context;
    //获取源数据
    __unsafe_unretained NSDictionary *dictionary = (__bridge NSDictionary *)(context->dictionary);
    //获取元类
    __unsafe_unretained _YYModelPropertyMeta *propertyMeta = (__bridge _YYModelPropertyMeta *)(_propertyMeta);
    //如果没有实现set方法，直接返回，防止crash
    if (!propertyMeta->_setter) return;
    id value = nil;
    
    // @{@"bookID": @[@"id", @"ID", @"book_id"]} 这种类型的解析方法
    if (propertyMeta->_mappedToKeyArray) {
        value = YYValueForMultiKeys(dictionary, propertyMeta->_mappedToKeyArray);
    }
    // @{@"desc"  : @"ext.desc"} 这种类型的解析方法
    else if (propertyMeta->_mappedToKeyPath) {
        value = YYValueForKeyPath(dictionary, propertyMeta->_mappedToKeyPath);
    }
    // 默认的解析方式
    else {
        value = [dictionary objectForKey:propertyMeta->_mappedToKey];
    }
    
    //如果存在
    if (value) {
        __unsafe_unretained id model = (__bridge id)(context->model);
        ModelSetValueForProperty(model, value, propertyMeta);
    }
}

3.4 ModelSetValueForProperty

ModelSetValueForProperty
没什么好说的，都是调用objc_msgSend方法，为property赋值
// 调用者 方法 参数
((void (*)(id, SEL, id))(void *) objc_msgSend)((id)model, meta->_setter, value);