YYModel介紹

YYModel是一個針對iOS/OSX平臺的高性能的Model解析庫，是屬于YYKit的一個組件背零，創(chuàng)建是ibireme迎吵。

其實在YYModel出現(xiàn)之前，已經(jīng)有非常多的Model解析庫桑逝，例如JSONModel、Mantle和MJExtension俏让。

YYModel從易用性和性能方面均達到了最高水平楞遏。

性能

Model解析庫對比

特性

• High performance: The conversion performance is close to handwriting code.
• Automatic type conversion: The object types can be automatically converted.
• Type Safe: All data types will be verified to ensure type-safe during the conversion process.
• Non-intrusive: There is no need to make the model class inherit from other base class.
• Lightwight: This library contains only 5 files.
• Docs and unit testing: 100% docs coverage, 99.6% code coverage.

YYModel使用

簡單Model和JSON轉(zhuǎn)換

// JSON:
{
    "uid":123456,
    "name":"Harry",
    "created":"1965-07-31T00:00:00+0000"
}

// Model:
@interface User : NSObject
@property UInt64 uid;
@property NSString *name;
@property NSDate *created;
@end
@implementation User
@end

// Convert json to model:
User *user = [User yy_modelWithJSON:json];
    
// Convert model to json:
NSDictionary *json = [user yy_modelToJSONObject];

內(nèi)嵌Model

// JSON
{
    "author":{
        "name":"J.K.Rowling",
        "birthday":"1965-07-31T00:00:00+0000"
    },
    "name":"Harry Potter",
    "pages":256
}

// Model: (no need to do anything)
@interface Author : NSObject
@property NSString *name;
@property NSDate *birthday;
@end
@implementation Author
@end
    
@interface Book : NSObject
@property NSString *name;
@property NSUInteger pages;
@property Author *author;
@end
@implementation Book
@end

集合類型 - Array、Set

@class Shadow, Border, Attachment;

@interface Attributes
@property NSString *name;
@property NSArray *shadows; //Array<Shadow>
@property NSSet *borders; //Set<Border>
@property NSMutableDictionary *attachments; //Dict<NSString,Attachment>
@end

@implementation Attributes
+ (NSDictionary *)modelContainerPropertyGenericClass {
    // value should be Class or Class name.
    return @{@"shadows" : [Shadow class],
             @"borders" : Border.class,
             @"attachments" : @"Attachment" };
}
@end

YYModel代碼結(jié)構(gòu)

YYModel整個項目非常簡潔首昔，只有5個文件寡喝。

詳細分析

以一個例子來分析，外部是Book對象勒奇，內(nèi)部有一個Author對象预鬓。

    NSString *json = @"{ \
    \"author\":{ \
        \"name\":\"J.K.Rowling\", \
        \"birthday\":\"1965-07-31T00:00:00+0000\" \
    }, \
    \"name\":\"Harry Potter\", \
    \"pages\":256 \
    }";
    
    Book *book = [Book yy_modelWithJSON:json];

yy_modelWithJSON

入口從[NSObject yy_modelWithJSON]進入

+ (instancetype)yy_modelWithJSON:(id)json {
    NSDictionary *dic = [self _yy_dictionaryWithJSON:json];
    return [self yy_modelWithDictionary:dic];
}

_yy_dictionaryWithJSON：將JSON的數(shù)據(jù)（String或者NSData）轉(zhuǎn)換成NSDictionary，主要使用系統(tǒng)方法[NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:NULL];

yy_modelWithDictionary

+ (instancetype)yy_modelWithDictionary:(NSDictionary *)dictionary {
    ...
    Class cls = [self class];
    _YYModelMeta *modelMeta = [_YYModelMeta metaWithClass:cls];
    if (modelMeta->_hasCustomClassFromDictionary) {
        cls = [cls modelCustomClassForDictionary:dictionary] ?: cls;
    }
    
    NSObject *one = [cls new];
    if ([one yy_modelSetWithDictionary:dictionary]) return one;
    return nil;
}

modelCustomClassForDictionary - Model類可以重載這個方法赊颠，將JSON轉(zhuǎn)換成另外一個Model類
后續(xù)處理都放在了yy_modelSetWithDictionary這個方法

yy_modelSetWithDictionary

首先根據(jù)Class信息構(gòu)造出_YYModelMeta

_YYModelMeta *modelMeta = [_YYModelMeta metaWithClass:object_getClass(self)];

_YYModelMeta中包含如下屬性：

• YYClassInfo *_classInfo：類信息格二，例如class、superclass竣蹦、ivarInfo顶猜、methodInfos、propertyInfos
• NSDictionary *_mapper：屬性key和對應的_YYModelPropertyMeta

{
    author = "<_YYModelPropertyMeta: 0x6080000f5c00>";
    name = "<_YYModelPropertyMeta: 0x6080000f5b00>";
    pages = "<_YYModelPropertyMeta: 0x6080000f5b80>";
}

看下Name里面對應的_YYModelPropertyMeta的內(nèi)容：

_YYModelPropertyMeta

* _name: 對應的是property的名字
* _nsType：對應property的類型
* _getter：getter方法
* _setter：setter方法

• NSArray *_allPropertyMetas：所有的_YYModelPropertyMeta
• NSArray *_keyPathPropertyMetas：Array<_YYModelPropertyMeta>, property meta which is mapped to a key path
• NSArray *_multiKeysPropertyMetas：Array<_YYModelPropertyMeta>, property meta which is mapped to multi keys.

數(shù)據(jù)填充

    if (modelMeta->_keyMappedCount >= CFDictionaryGetCount((CFDictionaryRef)dic)) {
        CFDictionaryApplyFunction((CFDictionaryRef)dic, ModelSetWithDictionaryFunction, &context);
        if (modelMeta->_keyPathPropertyMetas) {
            CFArrayApplyFunction((CFArrayRef)modelMeta->_keyPathPropertyMetas,
                                 CFRangeMake(0, CFArrayGetCount((CFArrayRef)modelMeta->_keyPathPropertyMetas)),
                                 ModelSetWithPropertyMetaArrayFunction,
                                 &context);
        }
        if (modelMeta->_multiKeysPropertyMetas) {
            CFArrayApplyFunction((CFArrayRef)modelMeta->_multiKeysPropertyMetas,
                                 CFRangeMake(0, CFArrayGetCount((CFArrayRef)modelMeta->_multiKeysPropertyMetas)),
                                 ModelSetWithPropertyMetaArrayFunction,
                                 &context);
        }
    } else {
        CFArrayApplyFunction((CFArrayRef)modelMeta->_allPropertyMetas,
                             CFRangeMake(0, modelMeta->_keyMappedCount),
                             ModelSetWithPropertyMetaArrayFunction,
                             &context);
    }

CFDictionaryApplyFunction/CFArrayApplyFunction：針對NSDictionary和NSArray的每一個值草添，執(zhí)行一個方法驶兜。Context作為方法中一個參數(shù)扼仲，帶入了Model的信息远寸。

Context數(shù)據(jù)結(jié)構(gòu)如下：

typedef struct {
    void *modelMeta;  ///< _YYModelMeta
    void *model;      ///< id (self)
    void *dictionary; ///< NSDictionary (json)
} ModelSetContext;

ModelSetWithDictionaryFunction

static void ModelSetWithDictionaryFunction(const void *_key, const void *_value, void *_context) {
    ModelSetContext *context = _context;
    __unsafe_unretained _YYModelMeta *meta = (__bridge _YYModelMeta *)(context->modelMeta);
    __unsafe_unretained _YYModelPropertyMeta *propertyMeta = [meta->_mapper objectForKey:(__bridge id)(_key)];
    __unsafe_unretained id model = (__bridge id)(context->model);
    while (propertyMeta) {
        if (propertyMeta->_setter) {
            ModelSetValueForProperty(model, (__bridge __unsafe_unretained id)_value, propertyMeta);
        }
        propertyMeta = propertyMeta->_next;
    };
}

這個方法是將Dictionary的數(shù)據(jù)填充到Model的核心過程。
通過Context獲取meta（Model的類信息）屠凶，通過meta獲取當前Key的propertyMeta（屬性信息）驰后，遞歸調(diào)用ModealSetValueForProperty填充model里面對應Key的Property。

ModelSetValueForProperty

這個方法會將數(shù)據(jù)填充到Model對應的Property中矗愧。

對于普通數(shù)據(jù)類型的數(shù)據(jù)填充灶芝，大體如下：

switch (meta->_nsType) {
                case YYEncodingTypeNSString:
                case YYEncodingTypeNSMutableString: {
                    if ([value isKindOfClass:[NSString class]]) {
                        if (meta->_nsType == YYEncodingTypeNSString) {
                            ((void (*)(id, SEL, id))(void *) objc_msgSend)((id)model, meta->_setter, value);
                        } else {
                            ((void (*)(id, SEL, id))(void *) objc_msgSend)((id)model, meta->_setter, ((NSString *)value).mutableCopy);
                        }
                    }

對于內(nèi)嵌的對象屬性郑原，處理如下：
Value通常是一個NSDicationary，如果有g(shù)etter方法夜涕，獲取這個property的對象犯犁，如果為nill則創(chuàng)建一個實例，再通過[one yy_modelSetWithDictionary:value]女器，填充這個property對象酸役。

            case YYEncodingTypeObject: {
                ...
                else if ([value isKindOfClass:[NSDictionary class]]) {
                    NSObject *one = nil;
                    if (meta->_getter) {
                        one = ((id (*)(id, SEL))(void *) objc_msgSend)((id)model, meta->_getter);
                    }
                    if (one) {
                        [one yy_modelSetWithDictionary:value];
                    } else {
                        Class cls = meta->_cls;
                        if (meta->_hasCustomClassFromDictionary) {
                            cls = [cls modelCustomClassForDictionary:value];
                            if (!cls) cls = meta->_genericCls; // for xcode code coverage
                        }
                        one = [cls new];
                        [one yy_modelSetWithDictionary:value];
                        ((void (*)(id, SEL, id))(void *) objc_msgSend)((id)model, meta->_setter, (id)one);
                    }
                }
            } break;

最佳實踐

force_inline

在YYModel實現(xiàn)中大量使用force_inline關(guān)鍵詞來修飾方法，inline的作用可以參考Wikipedia: Inline Function驾胆。Inline Function會在編譯階段將方法實現(xiàn)直接拷貝到調(diào)用處涣澡，減少方法參數(shù)傳遞和查找，可以提高運行效率丧诺。

YYMode的使用方法如下：

#define force_inline __inline__ __attribute__((always_inline))

static force_inline YYEncodingNSType YYClassGetNSType(Class cls) {
    ...
}

一次性初始化

對于一次性初始化的代碼盡量放在dispatch_once block中入桂，保證只會初始化一次。

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    cache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
    lock = dispatch_semaphore_create(1);
});

Lock

通過Lock來保證多線程執(zhí)行的一致性

static dispatch_semaphore_t lock;
dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
// do something
dispatch_semaphore_signal(lock);

緩存的實現(xiàn)

通過CFDictionaryCreateMutable實現(xiàn)了一個簡易的文件緩存驳阎，注意在讀取和寫入緩存的時候都使用了Lock來保證多線程一致性抗愁。

+ (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);
        lock = dispatch_semaphore_create(1);
    });
    dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
    _YYModelMeta *meta = CFDictionaryGetValue(cache, (__bridge const void *)(cls));
    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;
}

總結(jié)

YYModel是一個非常簡潔、高性能的Model解析庫呵晚，作者使用了大量的runtime方式解析class內(nèi)部信息驹愚，使用了inline、緩存劣纲、Lock等方式提高了性能和安全性逢捺。
多讀經(jīng)典的開源庫，理解作者的實現(xiàn)方式癞季，對于提高iOS設計和編程能力有很大的幫助劫瞳。