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 > 0) {
        
        NSMutableArray *argumentTypes = [NSMutableArray new];
        
        for (unsigned int i = 0; 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 = 0; i < num; i++) {
        
        objc_property_attribute_t att = attr[i];
        fprintf(stdout, "name = %s , value = %s 
",att.name , att.value);
    }
    
    const char *chars = property_getAttributes(property);
    fprintf(stdout, "%s 
",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 = 0;
    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 = 0; i < attrCount; i++) {
        
        // 3.1 根据objc_property_attribute_t 中的name 做一些事
        switch (attrs[i].name[0]) {
                
                // 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 > 3) {
                            char name[len - 2]; // 新建一个长度 = len - 2 的name字符数组 长度为5
                            name[len - 3] = '';   // 设置最后一个字符为
                            memcpy(name, attrs[i].value + 2, len - 3); // 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:1].uppercaseString, [_name substringFromIndex:1]]);
        }
    }
    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);

2016-05-23 16:00:12.134 ModelBenchmark[12626:245778] @"YYWeiboUser"

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

@property (nonatomic, assign) Example example;

2016-05-23 16:04:59.493 ModelBenchmark[12684:250528] {example=^id*iB^{example}}

objc_property_t property = class_getProperty([YYWeiboStatus class], "statusID");
    
    YYClassPropertyInfo *propertyInfo = [[YYClassPropertyInfo alloc] initWithProperty:property];

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

2016-05-23 16:06:39.747 ModelBenchmark[12696:252148] 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