YYModel 源码解读（二）之YYClassInfo.h (2)

 /**
  Instance variable information.
  */
 @interface YYClassIvarInfo : NSObject
 @property (nonatomic, assign, readonly) Ivar ivar;              ///< ivar opaque struct
 @property (nonatomic, strong, readonly) NSString *name;         ///< Ivar's name
 @property (nonatomic, assign, readonly) ptrdiff_t offset;       ///< Ivar's offset
 @property (nonatomic, strong, readonly) NSString *typeEncoding; ///< Ivar's type encoding
 @property (nonatomic, assign, readonly) YYEncodingType type;    ///< Ivar's type

 /**
  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;
 @end

上边代码通过创建Ivar(成员变量)的 抽象类， 返回我们需要的关于Ivar 的信息，

通过一个初始化方法创建，接下来我们看看该方法的具体实现

 - (instancetype)initWithIvar:(Ivar)ivar {
     // 初始化判空 如果为空 就返回nil
     if (!ivar) return nil;
     self = [super init];
     _ivar = ivar;

     // 获取成员变量的名称
     const char *name = ivar_getName(ivar);
     if (name) {

         // 把c的字符串转化成oc的字符串
         _name = [NSString stringWithUTF8String:name];
     }

     _offset = ivar_getOffset(ivar);

     // 获取类型编码
     const char *typeEncoding = ivar_getTypeEncoding(ivar);
     if (typeEncoding) {

         // 转为oc的字符穿
         _typeEncoding = [NSString stringWithUTF8String:typeEncoding];

         // 转成枚举值
         _type = YYEncodingGetType(typeEncoding);

     }
     return self;
 }

ivar_getName

ivar_getTypeEncoding

ivar_getOffset

这三个方法都是运行时方法，分别用来获取 名称 ， 类型编码 ， 偏移量 尤其要之处的是

ivar_getOffset方法： 官方文档中的描述是这样的

 Returns the offset of an instance variable.

 Declaration
 ptrdiff_t ivar_getOffset( Ivar ivar)
 Discussion
 For instance variables of type id or other object types, call object_getIvar and object_setIvar instead of using this offset to access the instance variable data directly.

ivar_getOffset函数，对于类型id或其它对象类型的实例变量，可以调用object_getIvar和object_setIvar来直接访问成员变量，而不使用偏移量。

接下来我们看看Method(方法)的 抽象类

 /**
  Method information.
  */
 @interface YYClassMethodInfo : NSObject
 @property (nonatomic, assign, readonly) Method method;                  ///< method opaque struct
 @property (nonatomic, strong, readonly) NSString *name;                 ///< method name
 @property (nonatomic, assign, readonly) SEL sel;                        ///< method's selector
 @property (nonatomic, assign, readonly) IMP imp;                        ///< method's implementation
 @property (nonatomic, strong, readonly) NSString *typeEncoding;         ///< method's parameter and return types
 @property (nonatomic, strong, readonly) NSString *returnTypeEncoding;   ///< return value's type
 @property (nullable, nonatomic, strong, readonly) NSArray<NSString *> *argumentTypeEncodings; ///< array of arguments' type

 /**
  Creates and returns a method info object.

  @param method method opaque struct
  @return A new object, or nil if an error occurs.
  */
 - (instancetype)initWithMethod:(Method)method;
 @end

这这段代码中 比较陌生的是Method 和 IMP

Method 是一个结构体:

struct objc_method
{
  SEL method_name;
  char * method_types;
  IMP method_imp;
};

1.方法名：方法名为此方法的方法签名，相同函数名和参数的方法名是一样的
2.方法类型： 描述方法的参数类型
3. 方法真实实现代码块的地址指针，可像C 一样直接调用

 - (instancetype)initWithMethod:(Method)method {
     if (!method) return nil;
     self = [super init];
     _method = method;

     // Method获取方法的名称
     _sel = method_getName(method);

     // 方法的实现地址
     _imp = method_getImplementation(method);

     // SEL 获取方法名
     const char *name = sel_getName(_sel);
     if (name) {
         _name = [NSString stringWithUTF8String:name];
     }

     // 获取类型
     const char *typeEncoding = method_getTypeEncoding(method);
     if (typeEncoding) {
         _typeEncoding = [NSString stringWithUTF8String:typeEncoding];
     }

     // 获取返回值类型
     char *returnType = method_copyReturnType(method);
     if (returnType) {
         _returnTypeEncoding = [NSString stringWithUTF8String:returnType];

         // 但凡 通过copy retain alloc 系统方法得到的内存，必须使用relea() 或 free() 进行释放
         free(returnType);
     }

     // 获取参数列表
     unsigned int argumentCount = method_getNumberOfArguments(method);
     if (argumentCount > ) {

         NSMutableArray *argumentTypes = [NSMutableArray new];

         for (unsigned int i = ; i < argumentCount; i++) {

             // 获取参数中的某一个参数
             char *argumentType = method_copyArgumentType(method, i);

             NSString *type = argumentType ? [NSString stringWithUTF8String:argumentType] : nil;
             [argumentTypes addObject:type ? type : @""];
             if (argumentType) free(argumentType);
         }
         _argumentTypeEncodings = argumentTypes;
     }
     return self;
 }

上边的代码使用了运行时中 关于Method 的一些方法，再次不做介绍，但值得注意的是

 但凡 通过copy retain alloc 系统方法得到的内存，必须使用relea() 或 free() 进行释放

 /**
  Property information.
  */
 @interface YYClassPropertyInfo : NSObject
 @property (nonatomic, assign, readonly) objc_property_t property; ///< property's opaque struct
 @property (nonatomic, strong, readonly) NSString *name;           ///< property's name
 @property (nonatomic, assign, readonly) YYEncodingType type;      ///< property's type
 @property (nonatomic, strong, readonly) NSString *typeEncoding;   ///< property's encoding value
 @property (nonatomic, strong, readonly) NSString *ivarName;       ///< property's ivar name
 @property (nullable, nonatomic, assign, readonly) Class cls;      ///< may be nil
 @property (nonatomic, assign, readonly) SEL getter;               ///< getter (nonnull)
 @property (nonatomic, assign, readonly) SEL setter;               ///< setter (nonnull)

 /**
  Creates and returns a property info object.

  @param property property opaque struct
  @return A new object, or nil if an error occurs.
  */
 - (instancetype)initWithProperty:(objc_property_t)property;

上边的类是对属性的抽象类，让我们通过下边的代码 了解下属性编码的知识

     objc_property_t property = class_getProperty([YYWeiboStatus class], "user");

     unsigned int num;
     objc_property_attribute_t *attr = property_copyAttributeList(property, &num);
     for (unsigned int i = ; i < num; i++) {

         objc_property_attribute_t att = attr[i];
         fprintf(stdout, "name = %s , value = %s \n",att.name , att.value);
     }

     const char *chars = property_getAttributes(property);
     fprintf(stdout, "%s \n",chars);

打印的输出结果为

 name = T , value = @"YYWeiboUser"
 name = & , value =
 name = N , value =
 name = V , value = _user
 T@"YYWeiboUser",&,N,V_user 

可以看出，比较重要的是属性的编码都是以T开头 标示属性的类型  以V开头 标示属性的变量名

 - (instancetype)initWithProperty:(objc_property_t)property {
     if (!property) return nil;
     self = [self init];

     _property = property;

     // 1. 获取属性名称
     const char *name = property_getName(property);
     if (name) {
         _name = [NSString stringWithUTF8String:name];
     }

     // 2.获取每一个属性的编码字符串
     YYEncodingType type = ;
     unsigned int attrCount;
     objc_property_attribute_t *attrs = property_copyAttributeList(property, &attrCount);

     // 3. 编译每一个属性的 objc_property_attribute_t
     for (unsigned int i = ; i < attrCount; i++) {

         // 3.1 根据objc_property_attribute_t 中的name 做一些事
         switch (attrs[i].name[]) {

                 // T 代码属性的类型编码
             case 'T': { // Type encoding
                 if (attrs[i].value) {
                     _typeEncoding = [NSString stringWithUTF8String:attrs[i].value];
                     type = YYEncodingGetType(attrs[i].value);

                     // 计算属性的实体类型 比如:@"User"
                     if ((type & YYEncodingTypeMask) == YYEncodingTypeObject) {

                         size_t len = strlen(attrs[i].value); // len = 7
                         if (len > ) {
                             char name[len - ]; // 新建一个长度 = len - 2 的name字符数组 长度为5
                             name[len - ] = '\0';   // 设置最后一个字符为\0
                             memcpy(name, attrs[i].value + , len - ); // copy USer 到name 中，

                             // 获取name 的真实实体类型
                             _cls = objc_getClass(name);
                         }
                     }
                 }
             } break;
             case 'V': { // Instance variable
                 if (attrs[i].value) {
                     _ivarName = [NSString stringWithUTF8String:attrs[i].value];
                 }
             } break;
             case 'R': {
                 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': { // getter 方法
                 type |= YYEncodingTypePropertyCustomGetter;
                 if (attrs[i].value) {
                     _getter = NSSelectorFromString([NSString stringWithUTF8String:attrs[i].value]);
                 }
             } break;
             case 'S': { // setter 方法
                 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) {
         free(attrs);
         attrs = NULL;
     }

     _type = type;

     // 获取setter 和 getter 方法
     if (_name.length) {
         if (!_getter) {
             _getter = NSSelectorFromString(_name);
         }
         if (!_setter) {
             _setter = NSSelectorFromString([NSString stringWithFormat:@"set%@%@:", [_name substringToIndex:].uppercaseString, [_name substringFromIndex:]]);
         }
     }
     return self;
 }

最后让我来看看打印结果

  objc_property_t property = class_getProperty([YYWeiboStatus class], "user");

     YYClassPropertyInfo *propertyInfo = [[YYClassPropertyInfo alloc] initWithProperty:property];

     NSLog(@"%@",propertyInfo.typeEncoding);

 -- ::12.134 ModelBenchmark[:] @"YYWeiboUser"

 typedef struct example {
     int* aPint;
     double  aDouble;
     char *aString;
     int  anInt;
     BOOL isMan;
     struct example *next;
 } Example;

 @property (nonatomic, assign) Example example;

 -- ::59.493 ModelBenchmark[:] {example=^id*iB^{example}}

 objc_property_t property = class_getProperty([YYWeiboStatus class], "statusID");

     YYClassPropertyInfo *propertyInfo = [[YYClassPropertyInfo alloc] initWithProperty:property];

     NSLog(@"%@",propertyInfo.typeEncoding);

 -- ::39.747 ModelBenchmark[:] Q

到此 关于 Ivar Method Property  的抽象类已经介绍完毕，在后面的使用中 直接使用这些抽象类来进行编码的