(20170207)开源第三方学习之JSONModel

1：仓库地址：https://github.com/jsonmodel/jsonmodel

 

主要作用是把JSON字符串转成Model实体，也可以把实体转化成JSON字符串；还包含一些转字典的内容；JOSN字符串通过AFNetworking转化成字典，然后再能过字典跟实体进行转换；

 

2：原理实现：

 

主要介绍关于实体对象转换地原理，其它不在这个里面进行介绍；其主要还是运用运用时的机制，对属性进行获取换进行处理； 

-(id)initWithDictionary:(NSDictionary*)dict error:(NSError**)err
{
    //check for nil input
    //1.为空判断
    if (!dict) {
        if (err) *err = [JSONModelError errorInputIsNil];
        return nil;
    }

    //invalid input, just create empty instance
    //2.类型判断
    if (![dict isKindOfClass:[NSDictionary class]]) {
        if (err) *err = [JSONModelError errorInvalidDataWithMessage:@"Attempt to initialize JSONModel object using initWithDictionary:error: but the dictionary parameter was not an 'NSDictionary'."];
        return nil;
    }

    //create a class instance
    //3.核心，初始化映射property
    self = [self init];
    if (!self) {

        //super init didn't succeed
        if (err) *err = [JSONModelError errorModelIsInvalid];
        return nil;
    }

    //check incoming data structure
    //4.检查映射结构是否能够从dictionary中找到相应的数据
    if (![self __doesDictionary:dict matchModelWithKeyMapper:self.__keyMapper error:err]) {
        return nil;
    }

    //import the data from a dictionary
    //5.进行数据赋值
    if (![self __importDictionary:dict withKeyMapper:self.__keyMapper validation:YES error:err]) {
        return nil;
    }

    //run any custom model validation
    //6.本地数据检查
    if (![self validate:err]) {
        return nil;
    }

    //model is valid! yay!
    return self;
}

2.1：如何获得属性相关修饰符？采用运行时的机制，获取实体中的属性，并通过属性获取对应的修饰符；不同的字符跟符号代表不一样的修饰符；

 

代码： 

        unsigned int propertyCount;
        objc_property_t *properties = class_copyPropertyList(class, &propertyCount);

        //loop over the class properties
        for (unsigned int i = ; i < propertyCount; i++) {

            JSONModelClassProperty* p = [[JSONModelClassProperty alloc] init];

            //get property name
            objc_property_t property = properties[i];
            const char *propertyName = property_getName(property);
            p.name = @(propertyName);

            //JMLog(@"property: %@", p.name);

            //get property attributes
            const char *attrs = property_getAttributes(property);
            NSString* propertyAttributes = @(attrs);
            NSArray* attributeItems = [propertyAttributes componentsSeparatedByString:@",”];
            …….
}

property_getAttributes函数返回objc_property_attribute_t结构体列表，objc_property_attribute_t结构体包含name和value，常用的属性如下：

 

属性类型  name值：T  value：变化

编码类型  name值：C(copy) &(strong) W(weak)空(assign) 等 value：无

非/原子性 name值：空(atomic) N(Nonatomic)  value：无

变量名称  name值：V  value：变化

 

 

使用property_getAttributes获得的描述是property_copyAttributeList能获取到的所有的name和value的总体描述，如 T@"NSDictionary",C,N,V_dict1

 

2.2 通过NSScanner用于在字符串中扫描指定的字符，尤其是把它们翻译/转换为数字和别的字符串。可以在创建NSScaner时指定它的string属性，然后scanner会按照你的要求从头到尾地扫描这个字符串的每个字符。 

NSScanner* scanner = nil;
            scanner = [NSScanner scannerWithString: propertyAttributes];

            //JMLog(@"attr: %@", [NSString stringWithCString:attrs encoding:NSUTF8StringEncoding]);
            [scanner scanUpToString:@"T" intoString: nil];
            [scanner scanString:@"T" intoString:nil];

            //check if the property is an instance of a class
            if ([scanner scanString:@"@\"" intoString: &propertyType]) {

                [scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@"\"<"]
                                        intoString:&propertyType];

                //JMLog(@"type: %@", propertyClassName);
                p.type = NSClassFromString(propertyType);
                p.isMutable = ([propertyType rangeOfString:@"Mutable"].location != NSNotFound);
                p.isStandardJSONType = [allowedJSONTypes containsObject:p.type];

                //read through the property protocols
                while ([scanner scanString:@"<" intoString:NULL]) {

                    NSString* protocolName = nil;

                    [scanner scanUpToString:@">" intoString: &protocolName];

                    if ([protocolName isEqualToString:@"Optional"]) {
                        p.isOptional = YES;
                    } else if([protocolName isEqualToString:@"Index"]) {
                        p.isIndex = YES;
                        objc_setAssociatedObject(
                                                 self.class,
                                                 &kIndexPropertyNameKey,
                                                 p.name,
                                                 OBJC_ASSOCIATION_RETAIN // This is atomic
                                                 );
                    } else if([protocolName isEqualToString:@"ConvertOnDemand"]) {
                        p.convertsOnDemand = YES;
                    } else if([protocolName isEqualToString:@"Ignore"]) {
                        p = nil;
                    } else {
                        p.protocol = protocolName;
                    }

                    [scanner scanString:@">" intoString:NULL];
                }

            }
            //check if the property is a structure
            else if ([scanner scanString:@"{" intoString: &propertyType]) {
                [scanner scanCharactersFromSet:[NSCharacterSet alphanumericCharacterSet]
                                    intoString:&propertyType];

                p.isStandardJSONType = NO;
                p.structName = propertyType;

            }
            //the property must be a primitive
            else {

                //the property contains a primitive data type
                [scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@","]
                                        intoString:&propertyType];

                //get the full name of the primitive type
                propertyType = valueTransformer.primitivesNames[propertyType];

                if (![allowedPrimitiveTypes containsObject:propertyType]) {

                    //type not allowed - programmer mistaked -> exception
                    @throw [NSException exceptionWithName:@"JSONModelProperty type not allowed"
                                                   reason:[NSString stringWithFormat:@"Property type of %@.%@ is not supported by JSONModel.", self.class, p.name]
                                                 userInfo:nil];
                }

            }

然后对符号的字符串进行解析分析，把相应的字符串获取到进行判断处理；对于有增加相应的属性进行操作，如忽略、可为空等，如是block修饰的也直接置空属性，不对它进行转换；代码如下：

NSString *nsPropertyName = @(propertyName);
            if([[self class] propertyIsOptional:nsPropertyName]){
                p.isOptional = YES;
            }

            if([[self class] propertyIsIgnored:nsPropertyName]){
                p = nil;
            }

            //few cases where JSONModel will ignore properties automatically
            if ([propertyType isEqualToString:@"Block"]) {
                p = nil;
            }

2.3 JSONModel关于keyMapper修改对应的属性对应名称

 

下面这段平时我们用于替换Model跟JSON字符串不一样的地方，重新给它命名一个属性新名字； 

 

+(JSONKeyMapper*)keyMapper
{
    return [[JSONKeyMapper alloc] initWithDictionary:@{
                                                       @"new_password": @"my_new_password",
                                                       }];
}

其实是在JSONModel初始化过程中有对keyMapper进行一个判断处理；判断当前的实体对象中是否有这个方法，如果有且还没有被映射缓存过，则对它进行处理；

    id mapper = [[self class] keyMapper];
    if ( mapper && !objc_getAssociatedObject(self.class, &kMapperObjectKey) ) {
        objc_setAssociatedObject(
                                 self.class,
                                 &kMapperObjectKey,
                                 mapper,
                                 OBJC_ASSOCIATION_RETAIN // This is atomic
                                 );
    }

其中关于&kClassPropertiesKey， &kMapperObjectKey的运用说明，是映射缓存的标识；

  //使用AssociateObject进行映射property的缓存，判断是否映射过
    if (!objc_getAssociatedObject(self.class, &kClassPropertiesKey)) {
        [self __inspectProperties];
    }

//同样使用AssociateObject进行映射property的缓存
if ( mapper && !objc_getAssociatedObject(self.class, &kMapperObjectKey) ) {
}

写入标识的操作如下：

    objc_setAssociatedObject(
                             self.class,
                             &kClassPropertiesKey,
                             [propertyIndex copy],
                             OBJC_ASSOCIATION_RETAIN // This is atomic
                             );

2.4 关于健值是否缺少判断

 

获取到当前实体的属性值，对于那些可空的就不进行判断，也就没有放在下面这个NSMutableSet里面 

-(NSMutableSet*)__requiredPropertyNames
{
    //fetch the associated property names
    NSMutableSet* classRequiredPropertyNames = objc_getAssociatedObject(self.class, &kClassRequiredPropertyNamesKey);

    if (!classRequiredPropertyNames) {
        classRequiredPropertyNames = [NSMutableSet set];
        [[self __properties__] enumerateObjectsUsingBlock:^(JSONModelClassProperty* p, NSUInteger idx, BOOL *stop) {
            if (!p.isOptional) [classRequiredPropertyNames addObject:p.name];
        }];

        //persist the list
        objc_setAssociatedObject(
                                 self.class,
                                 &kClassRequiredPropertyNamesKey,
                                 classRequiredPropertyNames,
                                 OBJC_ASSOCIATION_RETAIN // This is atomic
                                 );
    }
    return classRequiredPropertyNames;
}

这边要兼容除了dic字典里面的属性还要处理如果有KeyMapper的替换属性；然后进行统一判断；

-(BOOL)__doesDictionary:(NSDictionary*)dict matchModelWithKeyMapper:(JSONKeyMapper*)keyMapper error:(NSError**)err
{
    //check if all required properties are present
    NSArray* incomingKeysArray = [dict allKeys];
    NSMutableSet* requiredProperties = [self __requiredPropertyNames];
    NSSet* incomingKeys = [NSSet setWithArray: incomingKeysArray];

    //transform the key names, if neccessary
    if (keyMapper || globalKeyMapper) {

        NSMutableSet* transformedIncomingKeys = [NSMutableSet setWithCapacity: requiredProperties.count];
        NSString* transformedName = nil;

        //loop over the required properties list
        for (JSONModelClassProperty* property in [self __properties__]) {

            transformedName = (keyMapper||globalKeyMapper) ? [self __mapString:property.name withKeyMapper:keyMapper importing:YES] : property.name;

            //chek if exists and if so, add to incoming keys
            id value;
            @try {
                value = [dict valueForKeyPath:transformedName];
            }
            @catch (NSException *exception) {
                value = dict[transformedName];
            }

            if (value) {
                [transformedIncomingKeys addObject: property.name];
            }
        }

        //overwrite the raw incoming list with the mapped key names
        incomingKeys = transformedIncomingKeys;
    }

    //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.class, requiredProperties);

        if (err) *err = [JSONModelError errorInvalidDataWithMissingKeys:requiredProperties];
        return NO;
    }

    //not needed anymore
    incomingKeys= nil;
    requiredProperties= nil;

    return YES;
}

2.5 开始进行赋值操作

 

首先获取到对应的属性列表数组 

-(NSArray*)__properties__
{
    //fetch the associated object
    NSDictionary* classProperties = objc_getAssociatedObject(self.class, &kClassPropertiesKey);
    if (classProperties) return [classProperties allValues];

    //if here, the class needs to inspect itself
    [self __setup__];

    //return the property list
    classProperties = objc_getAssociatedObject(self.class, &kClassPropertiesKey);
    return [classProperties allValues];
}

然后主要进行属性赋值

-(BOOL)__importDictionary:(NSDictionary*)dict withKeyMapper:(JSONKeyMapper*)keyMapper validation:(BOOL)validation error:(NSError**)err
{
    //loop over the incoming keys and set self's properties
    //循环遍历映射出来的JSONModelClassProperty结构体
    for (JSONModelClassProperty* property in [self __properties__]) {

        //convert key name ot model keys, if a mapper is provided
        //keyMapper映射，获取镇真正的值
        NSString* jsonKeyPath = (keyMapper||globalKeyMapper) ? [self __mapString:property.name withKeyMapper:keyMapper importing:YES] : property.name;
        //JMLog(@"keyPath: %@", jsonKeyPath);

        //general check for data type compliance
        id jsonValue;
        @try {
            jsonValue = [dict valueForKeyPath: jsonKeyPath];
        }
        @catch (NSException *exception) {
            jsonValue = dict[jsonKeyPath];
        }

        //check for Optional properties
        if (isNull(jsonValue)) {
            //skip this property, continue with next property
            if (property.isOptional || !validation) continue;

            if (err) {
                //null value for required property
                NSString* msg = [NSString stringWithFormat:@"Value of required model key %@ is null", property.name];
                JSONModelError* dataErr = [JSONModelError errorInvalidDataWithMessage:msg];
                *err = [dataErr errorByPrependingKeyPathComponent:property.name];
            }
            return NO;
        }

        Class jsonValueClass = [jsonValue class];
        BOOL isValueOfAllowedType = NO;

        //判断数据输入类型是不是允许的json类型
        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) {
                NSString* msg = [NSString stringWithFormat:@"Type %@ is not allowed in JSON.", NSStringFromClass(jsonValueClass)];
                JSONModelError* dataErr = [JSONModelError errorInvalidDataWithMessage:msg];
                *err = [dataErr errorByPrependingKeyPathComponent:property.name];
            }
            return NO;
        }

        //check if there's matching property in the model
        if (property) {

            // check for custom setter, than the model doesn't need to do any guessing
            // how to read the property's value from JSON
            // 使用对象相应的setter方法进行set
            if ([self __customSetValue:jsonValue forProperty:property]) {
                //skip to next JSON key
                continue;
            };

            // 0) handle primitives
            // 代表基础类型，比如int float等，直接使用kvc赋值
            if (property.type == nil && property.structName==nil) {

                //generic setter
                if (jsonValue != [self valueForKey:property.name]) {
                    [self setValue:jsonValue forKey: property.name];
                }

                //skip directly to the next key
                continue;
            }

            // 0.5) handle nils
            if (isNull(jsonValue)) {
                if ([self valueForKey:property.name] != nil) {
                    [self setValue:nil forKey: property.name];
                }
                continue;
            }

            // 1) check if property is itself a JSONModel
            // 判断子结构是否是一个JSONModel结构，进行递归遍历，先将子结构遍历完并赋值完成
            if ([self __isJSONModelSubClass:property.type]) {

                //initialize the property's model, store it
                JSONModelError* initErr = nil;
                id value = [[property.type alloc] initWithDictionary: jsonValue error:&initErr];

                if (!value) {
                    //skip this property, continue with next property
                    if (property.isOptional || !validation) continue;

                    // Propagate the error, including the property name as the key-path component
                    if((err != nil) && (initErr != nil))
                    {
                        *err = [initErr errorByPrependingKeyPathComponent:property.name];
                    }
                    return NO;
                }
                if (![value isEqual:[self valueForKey:property.name]]) {
                    [self setValue:value forKey: property.name];
                }

                //for clarity, does the same without continue
                continue;

            } else {

                // 2) check if there's a protocol to the property
                //  ) might or not be the case there's a built in transform for it
                // 是否包含protocol的字段，该字段主要用来表明array或者dictionary中的对象类型
                if (property.protocol) {

                    //JMLog(@"proto: %@", p.protocol);
                    //循环遍历子内容，将对应的类型赋给相应的array或者dictionary
                    jsonValue = [self __transform:jsonValue forProperty:property error:err];
                    if (!jsonValue) {
                        if ((err != nil) && (*err == nil)) {
                            NSString* msg = [NSString stringWithFormat:@"Failed to transform value, but no error was set during transformation. (%@)", property];
                            JSONModelError* dataErr = [JSONModelError errorInvalidDataWithMessage:msg];
                            *err = [dataErr errorByPrependingKeyPathComponent:property.name];
                        }
                        return NO;
                    }
                }

                // 3.1) handle matching standard JSON types
                // 判断标准的json类型，比如nsstring等
                if (property.isStandardJSONType && [jsonValue isKindOfClass: property.type]) {

                    //mutable properties
                    if (property.isMutable) {
                        jsonValue = [jsonValue mutableCopy];
                    }

                    //set the property value
                    if (![jsonValue isEqual:[self valueForKey:property.name]]) {
                        [self setValue:jsonValue forKey: property.name];
                    }
                    continue;
                }

                // 3.3) handle values to transform
                // 其他处理情况，主要是一些类型转换的情况，比如nsstring转换为nsurl等
                if (
                    (![jsonValue isKindOfClass:property.type] && !isNull(jsonValue))
                    ||
                    //the property is mutable
                    property.isMutable
                    ||
                    //custom struct property
                    property.structName
                    ) {

                    // searched around the web how to do this better
                    // but did not find any solution, maybe that's the best idea? (hardly)
                    // 获取真实的json数据类型
                    Class sourceClass = [JSONValueTransformer classByResolvingClusterClasses:[jsonValue class]];

                    //JMLog(@"to type: [%@] from type: [%@] transformer: [%@]", p.type, sourceClass, selectorName);

                    //build a method selector for the property and json object classes
                    // 通过property类型和json数据类型进行转换的判断
                    NSString* selectorName = [NSString stringWithFormat:@"%@From%@:",
                                              (property.structName? property.structName : property.type), //target name
                                              sourceClass]; //source name
                    SEL selector = NSSelectorFromString(selectorName);

                    //check for custom transformer
                    //是否有本地转换的方法
                    BOOL foundCustomTransformer = NO;
                    if ([valueTransformer respondsToSelector:selector]) {
                        foundCustomTransformer = YES;
                    } else {
                        //try for hidden custom transformer
                        selectorName = [NSString stringWithFormat:@"__%@",selectorName];
                        selector = NSSelectorFromString(selectorName);
                        if ([valueTransformer respondsToSelector:selector]) {
                            foundCustomTransformer = YES;
                        }
                    }

                    //check if there's a transformer with that name
                    if (foundCustomTransformer) {

                        //it's OK, believe me...
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
                        //transform the value
                        // 通过 JSONValueTransformer 进行类型转换
                        jsonValue = [valueTransformer performSelector:selector withObject:jsonValue];
#pragma clang diagnostic pop

                        if (![jsonValue isEqual:[self valueForKey:property.name]]) {
                            [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 mistake -> exception
                        @throw [NSException exceptionWithName:@"Type not allowed"
                                                       reason:[NSString stringWithFormat:@"%@ type not supported for %@.%@", property.type, [self class], property.name]
                                                     userInfo:nil];
                        return NO;
                    }

                } else {
                    // 3.4) handle "all other" cases (if any)
                    if (![jsonValue isEqual:[self valueForKey:property.name]]) {
                        [self setValue:jsonValue forKey: property.name];
                    }
                }
            }
        }
    }

    return YES;
}

其中获取到值对应的类型是否在支持的转化类型中

allowedJSONTypes = @[
                [NSString class], [NSNumber class], [NSDecimalNumber class], [NSArray class], [NSDictionary class], [NSNull class], //immutable JSON classes
                [NSMutableString class], [NSMutableArray class], [NSMutableDictionary class] //mutable JSON classes
            ];

            allowedPrimitiveTypes = @[
                @"BOOL", @"float", @"int", @"long", @"double", @"short",
                //and some famous aliases
                @"NSInteger", @"NSUInteger",
                @"Block"
            ];

然后上面的代码用于下面进行判断

Class jsonValueClass = [jsonValue class];
        BOOL isValueOfAllowedType = NO;

        for (Class allowedType in allowedJSONTypes) {
            if ( [jsonValueClass isSubclassOfClass: allowedType] ) {
                isValueOfAllowedType = YES;
                break;
            }
        }

2.6 定义空的协议用于区分一些属性标识

@protocol Ignore
@end

/**
* Protocol for defining optional properties in a JSON Model class. Use like below to define
* model properties that are not required to have values in the JSON input:
*
* @property (strong, nonatomic) NSString<Optional>* propertyName;
*
*/
@protocol Optional
@end

/**
* Protocol for defining index properties in a JSON Model class. Use like below to define
* model properties that are considered the Model's identifier (id).
*
* @property (strong, nonatomic) NSString<Index>* propertyName;
*
*/
@protocol Index
@end

//使所有对象可选兼容，避免编译器警告
@interface NSObject(JSONModelPropertyCompatibility)<Optional, Index, Ignore>
@end

特别是Optional为可空的标识例如我们给一个属性设置可空时 @property (nonatomic, copy) NSString<Optional> *current_status;，然后在上面获取属性的字符串中关于是否存在这个标识字符串，做一些属性的配置；它是被包含在<>里面；

while ([scanner scanString:@"<" intoString:NULL]) {

                    NSString* protocolName = nil;

                    [scanner scanUpToString:@">" intoString: &protocolName];

                    if ([protocolName isEqualToString:@"Optional"]) {
                        p.isOptional = YES;
                    } else if([protocolName isEqualToString:@"Index"]) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
                        p.isIndex = YES;
#pragma GCC diagnostic pop

                        objc_setAssociatedObject(
                                                 self.class,
                                                 &kIndexPropertyNameKey,
                                                 p.name,
                                                 OBJC_ASSOCIATION_RETAIN // This is atomic
                                                 );
                    } else if([protocolName isEqualToString:@"Ignore"]) {
                        p = nil;
                    } else {
                        p.protocol = protocolName;
                    }

                    [scanner scanString:@">" intoString:NULL];
                }

            }

 3：关于属性类型的获取实例

定义一个类：

@interface MPAllModel : JSONModel

@property(nonatomic,copy)NSString *name;
@property(nonatomic,strong)NSString *userName;
@property(nonatomic)int age;
@property(nonatomic)float price;
@property(nonatomic,strong)NSNumber *isShow;
@property(nonatomic,assign)BOOL isError;
@property(nonatomic,strong)NSArray *itemArray;
@property(nonatomic,strong)NSArray<Optional> *dataArray;
@end

然后利用运行时的代码，获得到这个类对应属性的字符串内容：

    unsigned int outCount;
    int i;
    objc_property_t *property = class_copyPropertyList([MPAllModel class], &outCount);
    for (i = outCount -; i >=  ; i--) {
        NSString *getPropertyName = [NSString stringWithCString:property_getName(property[i]) encoding:NSUTF8StringEncoding];
        NSLog(@"getPropertyName:        %@",getPropertyName);
        NSString *getPropertyNameString = [NSString stringWithCString:property_getAttributes(property[i]) encoding:NSUTF8StringEncoding];
        NSLog(@"getPropertyNameString:  %@",getPropertyNameString);
    }

得到下面对应的类型：

getPropertyName:        dataArray
getPropertyNameString:  T@"NSArray<Optional>",&,N,V_dataArray

getPropertyName:        itemArray
getPropertyNameString:  T@"NSArray",&,N,V_itemArray

getPropertyName:        isError
getPropertyNameString:  TB,N,V_isError

getPropertyName:        isShow
getPropertyNameString:  T@"NSNumber",&,N,V_isShow

getPropertyName:        price
getPropertyNameString:  Tf,N,V_price

getPropertyName:        age
getPropertyNameString:  Ti,N,V_age

getPropertyName:        userName
getPropertyNameString:  T@"NSString",&,N,V_userName

getPropertyName:        name
getPropertyNameString:  T@"NSString",C,N,V_name

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