JSONModel源码阅读笔记

JSONModel是一个解析服务器返回的Json数据的库。

通常服务器传回的json数据要通过写一个数据转换模块将NSDictionary转换为Model,将NSString数据转换为Model中property的数据类型。

这样服务器如果要做修改,可能需要改两三个文件。

JSONModel的出现就是为了将这种解析工作在设计层面完成。

使用方法:参考连接

对其源码的核心部分JSONModel.m做了源码阅读,笔记如下:

-(id)initWithDictionary:(NSDictionary*)dict error:(NSError**)err
函数中完成所有解析工作:如果有任何失误或者错误直接返回nil。

-(id)initWithDictionary:(NSDictionary*)dict error:(NSError**)err
{
    //1、做有效性判断(dict是不是空啊,dict是不是真是一个NSDictionary)
    //check for nil input
    if (!dict) {
        if (err) *err = [JSONModelError errorInputIsNil];
        return nil;
    }

    //invalid input, just create empty instance
    if (![dict isKindOfClass:[NSDictionary class]]) {
        if (err) *err = [JSONModelError errorInvalidData];
        return nil;
    }

    //create a class instance
    self = [super init];
    if (!self) {
        
        //super init didn't succeed
        if (err) *err = [JSONModelError errorModelIsInvalid];
        return nil;
    }
    
    //__setup__中通过调用__restrospectProperties建立类属性的映射表,并且存放在全局变量classProperties里面
    //->__restrospectProperties中利用runtime function搞出属性列表:
    //    ->获得属性列表class_copyPropertyList(得到objc_property_t数组)->对于每一个objc_property_t调用property_getName获得名称,property_getAttributes获得属性的描述(字符串)->通过解析字符串获得属性的类型、是否是Mutable、是否是基本的JSON类型等等
    //    ->调用[class superclass]获得父类继续获取列表
    //    ->列表保存在classProperties中备用
    //->调用+keyMapper获得key转换列表,生成JSONKeyMapper对象存入keyMapper。
    //do initial class setup, retrospec properties
    [self __setup__];
    
    //看看必传参数中是否在输入参数中都有。
    //check if all required properties are present
    NSArray* incomingKeysArray = [dict allKeys];
    NSMutableSet* requiredProperties = [self __requiredPropertyNames];
    NSSet* incomingKeys = [NSSet setWithArray: incomingKeysArray];
    
    //get the key mapper
    JSONKeyMapper* keyMapper = keyMappers[__className_];
    
    //transform the key names, if neccessary
    if (keyMapper) {
        //对比dict输入的keyName导入NSSet与keyMapper中JSONKeyMapper对象做keyName的转换。统一转换为对象的propertyname。
        NSMutableSet* transformedIncomingKeys = [NSMutableSet setWithCapacity: requiredProperties.count];
        NSString* transformedName = nil;

        //loop over the required properties list
        for (NSString* requiredPropertyName in requiredProperties) {

            //get the mapped key path
            transformedName = keyMapper.modelToJSONKeyBlock(requiredPropertyName);
            
            //chek if exists and if so, add to incoming keys
            if ([dict valueForKeyPath:transformedName]) {
                [transformedIncomingKeys addObject: requiredPropertyName];
            }
        }
        
        //overwrite the raw incoming list with the mapped key names
        incomingKeys = transformedIncomingKeys;
    }
    
    //利用NSSet的isSubsetOfSet:将必传参数表与输入的keyName表对比。如果不是包含关系说明参数传的不够。
    //check for missing input keys
    if (![requiredProperties isSubsetOfSet:incomingKeys]) {

        //get a list of the missing properties
        [requiredProperties minusSet:incomingKeys];

        //not all required properties are in - invalid input
        JMLog(@"Incoming data was invalid [%@ initWithDictionary:]. Keys missing: %@", self._className_, requiredProperties);
        
        if (err) *err = [JSONModelError errorInvalidDataWithMissingKeys:requiredProperties];
        return nil;
    }
    
    //not needed anymore
    incomingKeys= nil;
    requiredProperties= nil;
    
    //从对象的classProperties列表中循环到dict中取值:(赋值使用KVO操作的setValue:forKey:来做的,这样会直接调用setter函数赋值)
    //loop over the incoming keys and set self's properties
    for (JSONModelClassProperty* property in [self __properties__]) {
        //对于每一个对象的property,通过keyMapper的转换找到对应dict property的dictKeyPath,找到值jsonValue。如果没有值,并且这个属性是Optional的就进行下一项property对比。
        //convert key name ot model keys, if a mapper is provided
        NSString* jsonKeyPath = property.name;
        
        if (keyMapper) jsonKeyPath = keyMapper.modelToJSONKeyBlock( property.name );

        //JMLog(@"keyPath: %@", jsonKeyPath);
        
        //general check for data type compliance
        id jsonValue = [dict valueForKeyPath: jsonKeyPath];
        
        //check for Optional properties
        if (jsonValue==nil && property.isOptional==YES) {
            //skip this property, continue with next property
            continue;
        }
        
        //对找到的值做类型判断,如果不是JSON应该返回的数据类型就报错。(注意:NSNull是可以作为参数回传的)
        Class jsonValueClass = [jsonValue class];
        BOOL isValueOfAllowedType = NO;
        
        for (Class allowedType in allowedJSONTypes) {
            if ( [jsonValueClass isSubclassOfClass: allowedType] ) {
                isValueOfAllowedType = YES;
                break;
            }
        }
        
        if (isValueOfAllowedType==NO) {
            //type not allowed
            JMLog(@"Type %@ is not allowed in JSON.", NSStringFromClass(jsonValueClass));

            if (err) *err = [JSONModelError errorInvalidData];
            return nil;
        }
                
        //check if there's matching property in the model
        //JSONModelClassProperty* property = classProperties[self.className][key];
        
        //接着对property的属性与jsonValue进行类型匹配:
        if (property) {
            
            //如果是基本类型(int/float等)直接值拷贝;
            // 0) handle primitives
            if (property.type == nil && property.structName==nil) {
                
                //just copy the value
                [self setValue:jsonValue forKey: property.name];
                
                //skip directly to the next key
                continue;
            }
            
            //如果是NSNull直接赋空值;
            // 0.5) handle nils
            if (isNull(jsonValue)) {
                [self setValue:nil forKey: property.name];
                continue;
            }

            //如果是值也是一个JsonModel,递归搞JsonModel
            // 1) check if property is itself a JSONModel
            if ([[property.type class] isSubclassOfClass:[JSONModel class]]) {
                
                //initialize the property's model, store it
                NSError* initError = nil;
                id value = [[property.type alloc] initWithDictionary: jsonValue error:&initError];

                if (!value) {
                    if (initError && err) *err = [JSONModelError errorInvalidData];
                    return nil;
                }
                [self setValue:value forKey: property.name];
                
                //for clarity, does the same without continue
                continue;
                
            } else {
                
                //如果property中有protocol解析将jsonValue按照protocol解析,如NSArray<JsonModelSubclass>,protocol就是JsonModelSubclass
                // 2) check if there's a protocol to the property
                //  ) might or not be the case there's a built in transofrm for it
                if (property.protocol) {
                    
                    //JMLog(@"proto: %@", p.protocol);
                    
                    //__transform:forProperty:函数功能:
                    //    ->先判断下protocolClass是否在运行环境中存在,如不存在并且property是NSArray类型,直接报错。否则,直接返回。
                    //    ->如果protocalClass是JsonModel的子类,
                    //    ->如果property.type是NSArray
                    //        ->判断一下是否是使用时转换
                    //        ->如果为使用时转换则输出一个JSONModelArray(NSArray)的子类
                    //        ->如果不是使用时转换则输出一个NSArray,其中的对象全部转换为protocalClass所对应对象
                    //    ->如果property.type是NSDictionary
                    //        ->将value转换为protocalClass所对应对象
                    //        ->根据key存储到一个NSDictionary中输出
                    jsonValue = [self __transform:jsonValue forProperty:property];
                    if (!jsonValue) {
                        if (err) *err = [JSONModelError errorInvalidData];
                        return nil;
                    }
                }
                
                //如果是基本JSON类型(NSString/NSNumber)
                // 3.1) handle matching standard JSON types
                if (property.isStandardJSONType && [jsonValue isKindOfClass: property.type]) {
                    
                    //如果是mutable的,做一份MutableCopy
                    //mutable properties
                    if (property.isMutable) {
                        jsonValue = [jsonValue mutableCopy];
                    }
                    
                    //set the property value
                    [self setValue:jsonValue forKey: property.name];
                    continue;
                }
                
                //如果property.type是NSArray
                // 3.3) handle values to transform
                if (
                    //如果(类型没有匹配,并且jsonValue不为空)或者是Mutable的property(说明是特殊类型转换)
                    (![jsonValue isKindOfClass:property.type] && !isNull(jsonValue))
                    ||
                    //the property is mutable
                    property.isMutable
                    ) {
                    
                    //利用JSONValueTransformer找到源类型
                    // searched around the web how to do this better
                    // but did not find any solution, maybe that's the best idea? (hardly)
                    Class sourceClass = [JSONValueTransformer classByResolvingClusterClasses:[jsonValue class]];
                    
                    //JMLog(@"to type: [%@] from type: [%@] transformer: [%@]", p.type, sourceClass, selectorName);
                    
                    //用字符串拼出转换函数的名称字符串,到JSONValueTransformer中去搜索@SEL执行出正确类型
                    //build a method selector for the property and json object classes
                    NSString* selectorName = [NSString stringWithFormat:@"%@From%@:",
                                              (property.structName? property.structName : property.type), //target name
                                              sourceClass]; //source name
                    SEL selector = NSSelectorFromString(selectorName);
                    
                    //check if there's a transformer with that name
                    if ([valueTransformer respondsToSelector:selector]) {
                        
                        //it's OK, believe me...
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
                        //transform the value
                        jsonValue = [valueTransformer performSelector:selector withObject:jsonValue];
#pragma clang diagnostic pop
                        
                        [self setValue:jsonValue forKey: property.name];
                        
                    } else {
                        
                        // it's not a JSON data type, and there's no transformer for it
                        // if property type is not supported - that's a programmer mistaked -> exception
                        @throw [NSException exceptionWithName:@"Type not allowed"
                                                       reason:[NSString stringWithFormat:@"%@ type not supported for %@.%@", property.type, [self class], property.name]
                                                     userInfo:nil];
                        return nil;
                    }
                    
                } else {
                    //哪儿都不是的直接存起来
                    // 3.4) handle "all other" cases (if any)
                    [self setValue:jsonValue forKey: property.name];
                }
            }
        }
    }
    
    //最后调用validate:看看结果是不是有效,没问题就返回了。
    //run any custom model validation
    NSError* validationError = nil;
    BOOL doesModelDataValidate = [self validate:&validationError];
    
    if (doesModelDataValidate == NO) {
        if (err) *err = validationError;
        return nil;
    }
    
    //model is valid! yay!
    return self;
}

程序亮点:
1、为了提高效率通过static的NSArray和NSDictionary进行解耦。
2、JSONValueTransformer实现了一个可复用的类型转换模板。
3、通过runtime function解析出property列表,通过property相关函数解析出名称,和Attributes的信息。
4、NSScanner的使用
5、NSSet的包含关系判断两个集合的交集
6、利用[NSObject setValue:forKey:]的KVO操作赋值,可以直接调用setter函数,并且可以赋nil到property中
7、适时给子类一个函数可以修改父类的一些行为

 
 
 
posted @ 2013-05-20 20:29 摇滚诗人 阅读(...) 评论(...) 编辑 收藏