YYModel源代码分析（二）YYClassInfo
前言
简书地址:http://www.jianshu.com/p/5428552be6ce
本文的中文注释代码demo更新在我的github上。
上篇 YYModel源代码分析（一）整体介绍
主要写了YYModel的整体结构，代码调用思路以及头文件YYModel.h代码。本篇会主要集中在YYClassInfo文件上。文章内容会包含一些与JSONModel的比较，想了解JSONModel，可以参考JSONModel源代码解析。
主体分层
YYClassInfo主要分为以下几部分：
typedef NS_OPTIONS(NSUInteger, YYEncodingType)与YYEncodingType YYEncodingGetType(const char *typeEncoding);方法@interface YYClassIvarInfo : NSObject@interface YYClassMethodInfo : NSObject@interface YYClassPropertyInfo : NSObject@interface YYClassInfo : NSObject
以下将分别分析每一部分的源代码。
YYClassInfo源代码
(1).typedef NS_OPTIONS(NSUInteger, YYEncodingType)与YYEncodingType YYEncodingGetType(const char *typeEncoding);方法
相关知识
在这边，对于YYEncodingType的了解，需要知道一个很重要的概念：
Type Encodings
To assist the runtime system, the compiler encodes the return and argument types for each method in a character string and associates the string with the method selector. The coding scheme it uses is also useful in other contexts and so is made publicly available with the@encode()
compiler directive. When given a type specification, @encode()
returns a string encoding that type. The type can be a basic type such as an int
, a pointer, a tagged structure or union, or a class name—any type, in fact, that can be used as an argument to the Csizeof()
operator.
看过我JSONModel解析的人，应该比较了解这一块，property attribute的解析就是通过type encode解析出来的string进行的解析。
但在这里的type encoding相对于JSONModel中的使用，会更general一些:
* JSONModel是只针对于Class的property变量，所以在解析的时候，将Ivar默认包含在property中，通过property的property attribute一并解析出来。
* YYModel中，包含了Class的property变量，还加上了Class的Method方法与Ivar的实例变量。对于Ivar来说，可能还存在在方法参数中，所以说所需要解析的类型会更加多一些。
代码
在YYClassInfo.h中，先定义了一个NS_OPTIONS：
typedef NS_OPTIONS(NSUInteger, YYEncodingType) {
//0~8位：变量类型
YYEncodingTypeMask = 0xFF, ///< mask of type value
YYEncodingTypeUnknown = 0, ///< unknown
YYEncodingTypeVoid = 1, ///< void
YYEncodingTypeBool = 2, ///< bool
YYEncodingTypeInt8 = 3, ///< char / BOOL
YYEncodingTypeUInt8 = 4, ///< unsigned char
YYEncodingTypeInt16 = 5, ///< short
YYEncodingTypeUInt16 = 6, ///< unsigned short
YYEncodingTypeInt32 = 7, ///< int
YYEncodingTypeUInt32 = 8, ///< unsigned int
YYEncodingTypeInt64 = 9, ///< long long
YYEncodingTypeUInt64 = 10, ///< unsigned long long
YYEncodingTypeFloat = 11, ///< float
YYEncodingTypeDouble = 12, ///< double
YYEncodingTypeLongDouble = 13, ///< long double
YYEncodingTypeObject = 14, ///< id
YYEncodingTypeClass = 15, ///< Class
YYEncodingTypeSEL = 16, ///< SEL
YYEncodingTypeBlock = 17, ///< block
YYEncodingTypePointer = 18, ///< void*
YYEncodingTypeStruct = 19, ///< struct
YYEncodingTypeUnion = 20, ///< union
YYEncodingTypeCString = 21, ///< char*
YYEncodingTypeCArray = 22, ///< char[10] (for example)
//8~16位：方法类型
YYEncodingTypeQualifierMask = 0xFF00, ///< mask of qualifier
YYEncodingTypeQualifierConst = 1 << 8, ///< const
YYEncodingTypeQualifierIn = 1 << 9, ///< in
YYEncodingTypeQualifierInout = 1 << 10, ///< inout
YYEncodingTypeQualifierOut = 1 << 11, ///< out
YYEncodingTypeQualifierBycopy = 1 << 12, ///< bycopy
YYEncodingTypeQualifierByref = 1 << 13, ///< byref
YYEncodingTypeQualifierOneway = 1 << 14, ///< oneway
//16~24位：property修饰类型
YYEncodingTypePropertyMask = 0xFF0000, ///< mask of property
YYEncodingTypePropertyReadonly = 1 << 16, ///< readonly
YYEncodingTypePropertyCopy = 1 << 17, ///< copy
YYEncodingTypePropertyRetain = 1 << 18, ///< retain
YYEncodingTypePropertyNonatomic = 1 << 19, ///< nonatomic
YYEncodingTypePropertyWeak = 1 << 20, ///< weak
YYEncodingTypePropertyCustomGetter = 1 << 21, ///< getter=
YYEncodingTypePropertyCustomSetter = 1 << 22, ///< setter=
YYEncodingTypePropertyDynamic = 1 << 23, ///< @dynamic
};该NS_OPTIONS主要定义了3个大类encode type:
* YYEncodingTypeMask:
变量类型，因为类型只会有一种，所以就用数字站位
* YYEncodingTypeQualifierMask:
方法中的参数变量修饰符，理论上只有解析Method的参数才能解析到
* YYEncodingTypePropertyMask
property修饰符类型
这边对于YYEncodingTypeQualifierMask和YYEncodingTypePropertyMask因为存在多种可能的情况，使用了位移(<<)的方式，通过与(&)YYEncodingTypeQualifierMask和YYEncodingTypePropertyMask的方式，判断是否包含某个值。
获取Ivar类型的函数如下：
//解析Ivar的type encode string
YYEncodingType YYEncodingGetType(const char *typeEncoding) {
char *type = (char *)typeEncoding;
if (!type) return YYEncodingTypeUnknown;
size_t len = strlen(type);
if (len == 0) return YYEncodingTypeUnknown;
YYEncodingType qualifier = 0;
bool prefix = true;
while (prefix) {
//方法参数Ivar中的解析，理论上解析不到该类参数
switch (*type) {
case 'r': {
qualifier |= YYEncodingTypeQualifierConst;
type++;
} break;
case 'n': {
qualifier |= YYEncodingTypeQualifierIn;
type++;
} break;
case 'N': {
qualifier |= YYEncodingTypeQualifierInout;
type++;
} break;
case 'o': {
qualifier |= YYEncodingTypeQualifierOut;
type++;
} break;
case 'O': {
qualifier |= YYEncodingTypeQualifierBycopy;
type++;
} break;
case 'R': {
qualifier |= YYEncodingTypeQualifierByref;
type++;
} break;
case 'V': {
qualifier |= YYEncodingTypeQualifierOneway;
type++;
} break;
default: { prefix = false; } break;
}
}
len = strlen(type);
if (len == 0) return YYEncodingTypeUnknown | qualifier;
//返回值类型解析
switch (*type) {
case 'v': return YYEncodingTypeVoid | qualifier;
case 'B': return YYEncodingTypeBool | qualifier;
case 'c': return YYEncodingTypeInt8 | qualifier;
case 'C': return YYEncodingTypeUInt8 | qualifier;
case 's': return YYEncodingTypeInt16 | qualifier;
case 'S': return YYEncodingTypeUInt16 | qualifier;
case 'i': return YYEncodingTypeInt32 | qualifier;
case 'I': return YYEncodingTypeUInt32 | qualifier;
case 'l': return YYEncodingTypeInt32 | qualifier;
case 'L': return YYEncodingTypeUInt32 | qualifier;
case 'q': return YYEncodingTypeInt64 | qualifier;
case 'Q': return YYEncodingTypeUInt64 | qualifier;
case 'f': return YYEncodingTypeFloat | qualifier;
case 'd': return YYEncodingTypeDouble | qualifier;
case 'D': return YYEncodingTypeLongDouble | qualifier;
case '#': return YYEncodingTypeClass | qualifier;
case ':': return YYEncodingTypeSEL | qualifier;
case '*': return YYEncodingTypeCString | qualifier;
case '^': return YYEncodingTypePointer | qualifier;
case '[': return YYEncodingTypeCArray | qualifier;
case '(': return YYEncodingTypeUnion | qualifier;
case '{': return YYEncodingTypeStruct | qualifier;
case '@': {
if (len == 2 && *(type + 1) == '?')
return YYEncodingTypeBlock | qualifier; //OC Block
else
return YYEncodingTypeObject | qualifier; //OC对象
}
default: return YYEncodingTypeUnknown | qualifier;
}
}该函数也是通过获得的type encode的string，对照着表进行解析，因为是解析Ivar,所以也只包含了YYEncodingTypeMask和YYEncodingTypeQualifierMask。而YYEncodingTypePropertyMask会包含在property的解析中。
(2).@interface YYClassIvarInfo : NSObject
相关知识
我下载了runtime的源代码objc4-680.tar.gz，以下代码基于该版本。该版本包含旧代码与新代码，以下全部基于新代码。
**Ivar:**An opaque type that represents an instance variable(实例变量，跟某个对象关联，不能被静态方法使用，与之想对应的是class variable).
typedef struct ivar_t *Ivar;
struct ivar_t {
#if __x86_64__
// *offset was originally 64-bit on some x86_64 platforms.
// We read and write only 32 bits of it.
// Some metadata provides all 64 bits. This is harmless for unsigned
// little-endian values.
// Some code uses all 64 bits. class_addIvar() over-allocates the
// offset for their benefit.
#endif
int32_t *offset;
const char *name;
const char *type;
// alignment is sometimes -1; use alignment() instead
uint32_t alignment_raw;
uint32_t size;
uint32_t alignment() const {
if (alignment_raw == ~(uint32_t)0) return 1U << WORD_SHIFT;
return 1 << alignment_raw;
}
};代码
YYClassIvarInfo类声明：
/** Instance variable information. */
@interface YYClassIvarInfo : NSObject
@property (nonatomic, assign, readonly) Ivar ivar; ///< ivar opaque struct ivar本身指针
@property (nonatomic, strong, readonly) NSString *name; ///< Ivar's name ivar名
@property (nonatomic, assign, readonly) ptrdiff_t offset; ///< Ivar's offset ivar偏移量
@property (nonatomic, strong, readonly) NSString *typeEncoding; ///< Ivar's type encoding ivar encode string
@property (nonatomic, assign, readonly) YYEncodingType type; ///< Ivar's type ivar encode解析值
/** Creates and returns an ivar info object. @param ivar ivar opaque struct @return A new object, or nil if an error occurs. */
- (instancetype)initWithIvar:(Ivar)ivar;
@endinitWithIvar方法实现：
- (instancetype)initWithIvar:(Ivar)ivar {
if (!ivar) return nil;
self = [super init];
_ivar = ivar;
const char *name = ivar_getName(ivar); //获取ivar名
if (name) {
_name = [NSString stringWithUTF8String:name];
}
_offset = ivar_getOffset(ivar); //获取便宜量
const char *typeEncoding = ivar_getTypeEncoding(ivar); //获取类型encode string
if (typeEncoding) {
_typeEncoding = [NSString stringWithUTF8String:typeEncoding];
_type = YYEncodingGetType(typeEncoding); //类型解析
}
return self;
}YYClassIvarInfo本身就是对系统Ivar的一层封装，并进行了一次类型的解析。
实例
用YYModel测试用例来进行观察：
YYTestNestRepo实现：
@interface YYTestNestRepo : NSObject
@property uint64_t repoID;
@property NSString *name;
@property YYTestNestUser *user;
@end
@implementation YYTestNestRepo
@endYYTestNestRepo调用：
NSString *json = @"{\"repoID\":1234,\"name\":\"YYModel\",\"user\":{\"uid\":5678,\"name\":\"ibireme\"}}";
YYTestNestRepo *repo = [YYTestNestRepo yy_modelWithJSON:json];设置解析断点在解析@property YYTestNestUser *user;的Ivar变量处：
(3).@interface YYClassMethodInfo : NSObject
相关知识
**Method:**An opaque type that represents a method in a class definition.
typedef struct method_t *Method;
struct method_t {
SEL name;
const char *types;
IMP imp;
struct SortBySELAddress :
public std::binary_function<const method_t&,
const method_t&, bool>
{
bool operator() (const method_t& lhs,
const method_t& rhs)
{ return lhs.name < rhs.name; }
};
};其中包含两个结构体SEL和IMP：
**SEL:**An opaque type that represents a method selector
Method selectors are used to represent the name of a method at runtime. A method selector is a C string that has been registered (or “mapped“) with the Objective-C runtime. Selectors generated by the compiler are automatically mapped by the runtime when the class is loaded.
typedef struct objc_selector *SEL;**IMP:**A pointer to the function of a method implementation
This data type is a pointer to the start of the function that implements the method. This function uses standard C calling conventions as implemented for the current CPU architecture. The first argument is a pointer to self (that is, the memory for the particular instance of this class, or, for a class method, a pointer to the metaclass). The second argument is the method selector. The method arguments follow.
#if !OBJC_OLD_DISPATCH_PROTOTYPES
typedef void (*IMP)(void /* id, SEL, ... */ );
#else
typedef id (*IMP)(id, SEL, ...);
#endif代码
YYClassMethodInfo类声明：
@interface YYClassMethodInfo : NSObject
@property (nonatomic, assign, readonly) Method method; ///< method opaque struct method指针
@property (nonatomic, strong, readonly) NSString *name; ///< method name method名
@property (nonatomic, assign, readonly) SEL sel; ///< method's selector method selector
@property (nonatomic, assign, readonly) IMP imp; ///< method's implementation method implementation
@property (nonatomic, strong, readonly) NSString *typeEncoding; ///< method's parameter and return types method的参数和返回类型
@property (nonatomic, strong, readonly) NSString *returnTypeEncoding; ///< return value's type method返回值的encode types
@property (nullable, nonatomic, strong, readonly) NSArray<NSString *> *argumentTypeEncodings; ///< array of arguments' type method参数列表
- (instancetype)initWithMethod:(Method)method;
@endinitWithMethod方法实现：
- (instancetype)initWithMethod:(Method)method { if (!method) return nil; self = [super init]; _method = method; _sel = method_getName(method); //获取方法名，在oc中，方法名就是selector的标志 _imp = method_getImplementation(method); //获取方法实现 const char *name = sel_getName(_sel); if (name) { _name = [NSString stringWithUTF8String:name]; } const char *typeEncoding = method_getTypeEncoding(method); //获得方法参数和返回值
if (typeEncoding) { _typeEncoding = [NSString stringWithUTF8String:typeEncoding]; }
char *returnType = method_copyReturnType(method); //获得返回值encode string
if (returnType) { _returnTypeEncoding = [NSString stringWithUTF8String:returnType]; free(returnType); }
unsigned int argumentCount = method_getNumberOfArguments(method); //获得方法参数数量
if (argumentCount > 0) { NSMutableArray *argumentTypes = [NSMutableArray new]; for (unsigned int i = 0; i < argumentCount; i++) { //遍历参数 char *argumentType = method_copyArgumentType(method, i); //获得该参数的encode string NSString *type = argumentType ? [NSString stringWithUTF8String:argumentType] : nil; [argumentTypes addObject:type ? type : @""]; if (argumentType) free(argumentType); }
_argumentTypeEncodings = argumentTypes;
}
return self;
}实例
用YYModel测试用例来进行观察：
YYTestNestRepo实现：
@interface YYTestNestRepo : NSObject
@property uint64_t repoID;
@property NSString *name;
@property YYTestNestUser *user;
@end
@implementation YYTestNestRepo
@endYYTestNestRepo调用：
NSString *json = @"{\"repoID\":1234,\"name\":\"YYModel\",\"user\":{\"uid\":5678,\"name\":\"ibireme\"}}";
YYTestNestRepo *repo = [YYTestNestRepo yy_modelWithJSON:json];设置解析断点解析user方法：
对于property来说，本质是:Ivar+getter+setter，所以设置了property也会触发initWithMethod解析-(YYTestNestUser *) user;方法，该方法的解析如上图。
这边比较有意思的是，明明user没有参数，怎么method_getNumberOfArguments解析出来2个参数
原因就是方法调用最后都会转成((void (*)(id, SEL))objc_msgSend)((id)m, @selector(user));，所以会有两个参数。
(4).@interface YYClassPropertyInfo : NSObject
相关知识
**Property:**An opaque type that represents an Objective-C declared property.
typedef struct property_t *objc_property_t;
struct property_t {
const char *name;
const char *attributes;
};其中对于attributes就是property属性的encode string。具体解析可以参考JSONModel的文章。
代码
YYClassPropertyInfo类声明：
@interface YYClassPropertyInfo : NSObject
@property (nonatomic, assign, readonly) objc_property_t property; ///< property's opaque struct property指针
@property (nonatomic, strong, readonly) NSString *name; ///< property's name property名
@property (nonatomic, assign, readonly) YYEncodingType type; ///< property's type property encode解析值
@property (nonatomic, strong, readonly) NSString *typeEncoding; ///< property's encoding value property encode string
@property (nonatomic, strong, readonly) NSString *ivarName; ///< property's ivar name property对应的ivar名字
@property (nullable, nonatomic, assign, readonly) Class cls; ///< may be nil property如果是oc类型，oc类型对应的class
@property (nullable, nonatomic, strong, readonly) NSArray<NSString *> *protocols; ///< may nil property如果存在protocol，protocol列表
@property (nonatomic, assign, readonly) SEL getter; ///< getter (nonnull) property的getter方法
@property (nonatomic, assign, readonly) SEL setter; ///< setter (nonnull) property的setter方法
- (instancetype)initWithProperty:(objc_property_t)property;
@endinitWithProperty方法实现：
- (instancetype)initWithProperty:(objc_property_t)property {
if (!property) return nil;
self = [super init];
_property = property;
const char *name = property_getName(property); //获得property名
if (name) {
_name = [NSString stringWithUTF8String:name];
}
YYEncodingType type = 0;
unsigned int attrCount;
objc_property_attribute_t *attrs = property_copyAttributeList(property, &attrCount); //获得所有property的attribute array
for (unsigned int i = 0; i < attrCount; i++) {
switch (attrs[i].name[0]) {
case 'T': { // Type encoding 表示是property类型
if (attrs[i].value) {
_typeEncoding = [NSString stringWithUTF8String:attrs[i].value]; //获得attribute的encode string
type = YYEncodingGetType(attrs[i].value); //解析type
if ((type & YYEncodingTypeMask) == YYEncodingTypeObject && _typeEncoding.length) { //代表是OC类型
NSScanner *scanner = [NSScanner scannerWithString:_typeEncoding]; //扫描attribute的encode string
if (![scanner scanString:@"@\"" intoString:NULL]) continue; //不包含@\"代表不是oc类型，跳过
NSString *clsName = nil;
if ([scanner scanUpToCharactersFromSet: [NSCharacterSet characterSetWithCharactersInString:@"\"<"] intoString:&clsName]) { //扫描oc类型string，在 \"之前
if (clsName.length) _cls = objc_getClass(clsName.UTF8String); //获得oc对象类型，并附值
}
NSMutableArray *protocols = nil;
while ([scanner scanString:@"<" intoString:NULL]) { //扫描<>中的protocol类型，并设置
NSString* protocol = nil;
if ([scanner scanUpToString:@">" intoString: &protocol]) {
if (protocol.length) {
if (!protocols) protocols = [NSMutableArray new];
[protocols addObject:protocol];
}
}
[scanner scanString:@">" intoString:NULL];
}
_protocols = protocols;
}
}
} break;
case 'V': { // Instance variable //ivar变量
if (attrs[i].value) {
_ivarName = [NSString stringWithUTF8String:attrs[i].value];
}
} break;
case 'R': { //以下为property的几种类型扫描,setter和getter方法要记录方法名
type |= YYEncodingTypePropertyReadonly;
} break;
case 'C': {
type |= YYEncodingTypePropertyCopy;
} break;
case '&': {
type |= YYEncodingTypePropertyRetain;
} break;
case 'N': {
type |= YYEncodingTypePropertyNonatomic;
} break;
case 'D': {
type |= YYEncodingTypePropertyDynamic;
} break;
case 'W': {
type |= YYEncodingTypePropertyWeak;
} break;
case 'G': {
type |= YYEncodingTypePropertyCustomGetter;
if (attrs[i].value) {
_getter = NSSelectorFromString([NSString stringWithUTF8String:attrs[i].value]);
}
} break;
case 'S': {
type |= YYEncodingTypePropertyCustomSetter;
if (attrs[i].value) {
_setter = NSSelectorFromString([NSString stringWithUTF8String:attrs[i].value]);
}
} // break; commented for code coverage in next line
default: break;
}
}
if (attrs) { //有attrs要free
free(attrs);
attrs = NULL;
}
_type = type; //最后设置encode解析值
if (_name.length) { //设置默认的getter方法和setter方法
if (!_getter) {
_getter = NSSelectorFromString(_name);
}
if (!_setter) {
_setter = NSSelectorFromString([NSString stringWithFormat:@"set%@%@:", [_name substringToIndex:1].uppercaseString, [_name substringFromIndex:1]]);
}
}
return self;
}这段的解析方式和之前JSONModel的解析property方式有些类似，也不多做介绍了。
实例
用YYModel测试用例来进行观察：
YYTestNestRepo实现：
@interface YYTestNestRepo : NSObject
@property uint64_t repoID;
@property NSString *name;
@property YYTestNestUser *user;
@end
@implementation YYTestNestRepo
@endYYTestNestRepo调用：
NSString *json = @"{\"repoID\":1234,\"name\":\"YYModel\",\"user\":{\"uid\":5678,\"name\":\"ibireme\"}}";
YYTestNestRepo *repo = [YYTestNestRepo yy_modelWithJSON:json];设置解析断点解析property-user：
(5).@interface YYClassInfo : NSObject
相关知识
**Class:**An opaque type that represents an Objective-C class.
typedef struct objc_class *Class;
struct objc_class : objc_object {
Class superclass;
const char *name;
uint32_t version;
uint32_t info;
uint32_t instance_size;
struct old_ivar_list *ivars;
struct old_method_list **methodLists;
Cache cache;
struct old_protocol_list *protocols;
// CLS_EXT only
const uint8_t *ivar_layout;
struct old_class_ext *ext;
...
}
struct objc_object {
private:
isa_t isa;
public:
...
}对Class的superclass和isa指针来说，网上有一个特别多转载的图：
上图实线是 super_class 指针，虚线是isa指针。 有趣的是根元类的超类是NSObject，而isa指向了自己，而NSObject的超类为nil，也就是它没有超类。
代码
YYClassInfo类声明：
@interface YYClassInfo : NSObject
@property (nonatomic, assign, readonly) Class cls; ///< class object class指针
@property (nullable, nonatomic, assign, readonly) Class superCls; ///< super class object superClass指针
@property (nullable, nonatomic, assign, readonly) Class metaCls; ///< class's meta class object metaClass指针
@property (nonatomic, readonly) BOOL isMeta; ///< whether this class is meta class 是否该class是metaclass
@property (nonatomic, strong, readonly) NSString *name; ///< class name class名
@property (nullable, nonatomic, strong, readonly) YYClassInfo *superClassInfo; ///< super class's class info superClass的classinfo（缓存）
@property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassIvarInfo *> *ivarInfos; ///< ivars ivar的dictionary,key为ivar的name
@property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassMethodInfo *> *methodInfos; ///< methods method的dictionary,key为method的name
@property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassPropertyInfo *> *propertyInfos; ///< properties properties的dictionary,key为property的name
//设置class更新，比如动态增加了一个方法，需要更新class
- (void)setNeedUpdate;
//返回class是否需要更新，更新则应该调用下面两个方法之一
- (BOOL)needUpdate;
+ (nullable instancetype)classInfoWithClass:(Class)cls;
+ (nullable instancetype)classInfoWithClassName:(NSString *)className;
@endYYClassInfo中有一个needUpdate是否更新的标识符，当手动更改class结构(比如class_addMethod()等)的时候，可以调用方法：
@implementation YYClassInfo {
BOOL _needUpdate; //是否需要更新private变量
}
- (void)setNeedUpdate { //设置需要更新
_needUpdate = YES;
}
- (BOOL)needUpdate { //返回是否需要更新
return _needUpdate;
}实际的解析方法：
//多一层class从nsstring到class对象的转换
+ (instancetype)classInfoWithClassName:(NSString *)className {
Class cls = NSClassFromString(className);
return [self classInfoWithClass:cls];
}
//class解析主体方法
+ (instancetype)classInfoWithClass:(Class)cls {
if (!cls) return nil;
static CFMutableDictionaryRef classCache; //class缓存
static CFMutableDictionaryRef metaCache; //meta class缓存
static dispatch_once_t onceToken;
static dispatch_semaphore_t lock; //锁
dispatch_once(&onceToken, ^{ //初始化两种缓存
classCache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
metaCache = CFDictionaryCreateMutable(CFAllocatorGetDefault(), 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
lock = dispatch_semaphore_create(1);
});
dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER); //只允许同时1个线程
YYClassInfo *info = CFDictionaryGetValue(class_isMetaClass(cls) ? metaCache : classCache, (__bridge const void *)(cls)); //获取曾经解析过的缓存
if (info && info->_needUpdate) { //如果存在且需要更新，则重新解析class并更新结构体
[info _update];
}
dispatch_semaphore_signal(lock); //释放锁
if (!info) { //如果没有缓存，则第一次解析class
info = [[YYClassInfo alloc] initWithClass:cls];
if (info) { //解析完毕设置缓存
dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
CFDictionarySetValue(info.isMeta ? metaCache : classCache, (__bridge const void *)(cls), (__bridge const void *)(info));
dispatch_semaphore_signal(lock);
}
}
return info;
}
classInfoWithClass方法中主要调用了两个方法- (instancetype)initWithClass:(Class)cls（初始化class）和- (void)_update（更新class），接下来看该两个方法的实现。
//初始化class对象方法
- (instancetype)initWithClass:(Class)cls {
if (!cls) return nil;
self = [super init];
_cls = cls;
_superCls = class_getSuperclass(cls); //设置superclass
_isMeta = class_isMetaClass(cls); //判断是否是metaclass
if (!_isMeta) { //不是的话获得meta class
_metaCls = objc_getMetaClass(class_getName(cls));
}
_name = NSStringFromClass(cls); //获得类名
[self _update]; //进行更新
_superClassInfo = [self.class classInfoWithClass:_superCls]; //递归superclass
return self;
}这边也用到了``- (void)_update（更新class），这应该就是class的核心更新方法：
//更新函数
- (void)_update {
_ivarInfos = nil; //重置ivar，mthod，property3个缓存dictionary
_methodInfos = nil;
_propertyInfos = nil;
Class cls = self.cls;
unsigned int methodCount = 0;
Method *methods = class_copyMethodList(cls, &methodCount);
if (methods) { //解析method，并以name为key，进行缓存设置
NSMutableDictionary *methodInfos = [NSMutableDictionary new];
_methodInfos = methodInfos;
for (unsigned int i = 0; i < methodCount; i++) {
YYClassMethodInfo *info = [[YYClassMethodInfo alloc] initWithMethod:methods[i]];
if (info.name) methodInfos[info.name] = info;
}
free(methods);
}
unsigned int propertyCount = 0;
objc_property_t *properties = class_copyPropertyList(cls, &propertyCount);
if (properties) { //解析property，并以name为key，进行缓存设置
NSMutableDictionary *propertyInfos = [NSMutableDictionary new];
_propertyInfos = propertyInfos;
for (unsigned int i = 0; i < propertyCount; i++) {
YYClassPropertyInfo *info = [[YYClassPropertyInfo alloc] initWithProperty:properties[i]];
if (info.name) propertyInfos[info.name] = info;
}
free(properties);
}
unsigned int ivarCount = 0;
Ivar *ivars = class_copyIvarList(cls, &ivarCount);
if (ivars) { //解析ivar，并以name为key，进行缓存设置
NSMutableDictionary *ivarInfos = [NSMutableDictionary new];
_ivarInfos = ivarInfos;
for (unsigned int i = 0; i < ivarCount; i++) {
YYClassIvarInfo *info = [[YYClassIvarInfo alloc] initWithIvar:ivars[i]];
if (info.name) ivarInfos[info.name] = info;
}
free(ivars);
}
if (!_ivarInfos) _ivarInfos = @{}; //如果不存在相应的方法，则初始化空的dictionary给相应的方法
if (!_methodInfos) _methodInfos = @{};
if (!_propertyInfos) _propertyInfos = @{};
_needUpdate = NO; //已经更新完成，设no
}该函数虽然比较长，但也比较好理解，就是将method,property,ivar全部取出并附值给缓存。
实例
用YYModel测试用例来进行观察：
YYTestNestRepo实现：
@interface YYTestNestRepo : NSObject
@property uint64_t repoID;
@property NSString *name;
@property YYTestNestUser *user;
@end
@implementation YYTestNestRepo
@endYYTestNestRepo调用：
NSString *json = @"{\"repoID\":1234,\"name\":\"YYModel\",\"user\":{\"uid\":5678,\"name\":\"ibireme\"}}";
YYTestNestRepo *repo = [YYTestNestRepo yy_modelWithJSON:json];设置解析断点解析class YYTestNestRepo：
至此，整个model的class信息全部被解析完成，然后设置到了YYClassInfo类型的上。
小结
相对于JSONModel只对Property进行解析然后缓存。
YYModel将Class的Method,Property,Ivar全部进行了解析与缓存。
其中比较亮点的地方：
* 1.Ivar和property解析出来的YYEncodingType
* 2.CFMutableDictionaryRef的缓存
* 3.可以动态更新的needUpdate
参考资料
1.郑钦洪_：YYModel 源码历险记
2.Objective-C Runtime Programming Guide - Declared Properties
3.Objective-C Runtime Programming Guide - Type Encodings
4.runtime源代码
5.Objective-C Runtime的数据类型
6.轻松学习之三——IMP指针的作用
7.runtime Method
8.apple-objective_c runtime
9.Objective-C Runtime