YYModel 源码解读（二）之YYClassInfo.h (2)

 1 /**
 2  Instance variable information.
 3  */
 4 @interface YYClassIvarInfo : NSObject
 5 @property (nonatomic, assign, readonly) Ivar ivar;              ///< ivar opaque struct
 6 @property (nonatomic, strong, readonly) NSString *name;         ///< Ivar's name
 7 @property (nonatomic, assign, readonly) ptrdiff_t offset;       ///< Ivar's offset
 8 @property (nonatomic, strong, readonly) NSString *typeEncoding; ///< Ivar's type encoding
 9 @property (nonatomic, assign, readonly) YYEncodingType type;    ///< Ivar's type
10 
11 /**
12  Creates and returns an ivar info object.
13  
14  @param ivar ivar opaque struct
15  @return A new object, or nil if an error occurs.
16  */
17 - (instancetype)initWithIvar:(Ivar)ivar;
18 @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

 1 - (instancetype)initWithIvar:(Ivar)ivar {
 2     // 初始化判空 如果为空 就返回nil
 3     if (!ivar) return nil;
 4     self = [super init];
 5     _ivar = ivar;
 6     
 7     // 获取成员变量的名称
 8     const char *name = ivar_getName(ivar);
 9     if (name) {
10         
11         // 把c的字符串转化成oc的字符串
12         _name = [NSString stringWithUTF8String:name];
13     }
14     
15     _offset = ivar_getOffset(ivar);
16     
17     // 获取类型编码
18     const char *typeEncoding = ivar_getTypeEncoding(ivar);
19     if (typeEncoding) {
20         
21         // 转为oc的字符穿
22         _typeEncoding = [NSString stringWithUTF8String:typeEncoding];
23         
24         // 转成枚举值
25         _type = YYEncodingGetType(typeEncoding);
26    
27     }
28     return self;
29 }
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
1 Returns the offset of an instance variable.
2 
3 Declaration
4 ptrdiff_t ivar_getOffset( Ivar ivar)
5 Discussion
6 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

 1 /**
 2  Method information.
 3  */
 4 @interface YYClassMethodInfo : NSObject
 5 @property (nonatomic, assign, readonly) Method method;                  ///< method opaque struct
 6 @property (nonatomic, strong, readonly) NSString *name;                 ///< method name
 7 @property (nonatomic, assign, readonly) SEL sel;                        ///< method's selector
 8 @property (nonatomic, assign, readonly) IMP imp;                        ///< method's implementation
 9 @property (nonatomic, strong, readonly) NSString *typeEncoding;         ///< method's parameter and return types
10 @property (nonatomic, strong, readonly) NSString *returnTypeEncoding;   ///< return value's type
11 @property (nullable, nonatomic, strong, readonly) NSArray<NSString *> *argumentTypeEncodings; ///< array of arguments' type
12 
13 /**
14  Creates and returns a method info object.
15  
16  @param method method opaque struct
17  @return A new object, or nil if an error occurs.
18  */
19 - (instancetype)initWithMethod:(Method)method;
20 @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
 1 - (instancetype)initWithMethod:(Method)method {
 2     if (!method) return nil;
 3     self = [super init];
 4     _method = method;
 5     
 6     // Method获取方法的名称
 7     _sel = method_getName(method);
 8     
 9     // 方法的实现地址
10     _imp = method_getImplementation(method);
11     
12     // SEL 获取方法名
13     const char *name = sel_getName(_sel);
14     if (name) {
15         _name = [NSString stringWithUTF8String:name];
16     }
17     
18     // 获取类型
19     const char *typeEncoding = method_getTypeEncoding(method);
20     if (typeEncoding) {
21         _typeEncoding = [NSString stringWithUTF8String:typeEncoding];
22     }
23     
24     // 获取返回值类型
25     char *returnType = method_copyReturnType(method);
26     if (returnType) {
27         _returnTypeEncoding = [NSString stringWithUTF8String:returnType];
28         
29         // 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
30         free(returnType);
31     }
32     
33     // 获取参数列表
34     unsigned int argumentCount = method_getNumberOfArguments(method);
35     if (argumentCount > 0) {
36         
37         NSMutableArray *argumentTypes = [NSMutableArray new];
38         
39         for (unsigned int i = 0; i < argumentCount; i++) {
40             
41             // 获取参数中的某一个参数
42             char *argumentType = method_copyArgumentType(method, i);
43             
44             NSString *type = argumentType ? [NSString stringWithUTF8String:argumentType] : nil;
45             [argumentTypes addObject:type ? type : @""];
46             if (argumentType) free(argumentType);
47         }
48         _argumentTypeEncodings = argumentTypes;
49     }
50     return self;
51 }

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

 1 /**
 2  Property information.
 3  */
 4 @interface YYClassPropertyInfo : NSObject
 5 @property (nonatomic, assign, readonly) objc_property_t property; ///< property's opaque struct
 6 @property (nonatomic, strong, readonly) NSString *name;           ///< property's name
 7 @property (nonatomic, assign, readonly) YYEncodingType type;      ///< property's type
 8 @property (nonatomic, strong, readonly) NSString *typeEncoding;   ///< property's encoding value
 9 @property (nonatomic, strong, readonly) NSString *ivarName;       ///< property's ivar name
10 @property (nullable, nonatomic, assign, readonly) Class cls;      ///< may be nil
11 @property (nonatomic, assign, readonly) SEL getter;               ///< getter (nonnull)
12 @property (nonatomic, assign, readonly) SEL setter;               ///< setter (nonnull)
13 
14 /**
15  Creates and returns a property info object.
16  
17  @param property property opaque struct
18  @return A new object, or nil if an error occurs.
19  */
20 - (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

 1     objc_property_t property = class_getProperty([YYWeiboStatus class], "user");
 2     
 3     unsigned int num;
 4     objc_property_attribute_t *attr = property_copyAttributeList(property, &num);
 5     for (unsigned int i = 0; i < num; i++) {
 6         
 7         objc_property_attribute_t att = attr[i];
 8         fprintf(stdout, "name = %s , value = %s 
",att.name , att.value);
 9     }
10     
11     const char *chars = property_getAttributes(property);
12     fprintf(stdout, "%s 
",chars);

打印的输出结果为

1 name = T , value = @"YYWeiboUser" 
2 name = & , value =  
3 name = N , value =  
4 name = V , value = _user 
5 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





  1 - (instancetype)initWithProperty:(objc_property_t)property {
  2     if (!property) return nil;
  3     self = [self init];
  4     
  5     _property = property;
  6     
  7     // 1. 获取属性名称
  8     const char *name = property_getName(property);
  9     if (name) {
 10         _name = [NSString stringWithUTF8String:name];
 11     }
 12     
 13     // 2.获取每一个属性的编码字符串
 14     YYEncodingType type = 0;
 15     unsigned int attrCount;
 16     objc_property_attribute_t *attrs = property_copyAttributeList(property, &attrCount);
 17     
 18     // 3. 编译每一个属性的 objc_property_attribute_t
 19     for (unsigned int i = 0; i < attrCount; i++) {
 20         
 21         // 3.1 根据objc_property_attribute_t 中的name 做一些事
 22         switch (attrs[i].name[0]) {
 23                 
 24                 // T 代码属性的类型编码
 25             case 'T': { // Type encoding
 26                 if (attrs[i].value) {
 27                     _typeEncoding = [NSString stringWithUTF8String:attrs[i].value];
 28                     type = YYEncodingGetType(attrs[i].value);
 29                     
 30                     // 计算属性的实体类型 比如:@"User"
 31                     if ((type & YYEncodingTypeMask) == YYEncodingTypeObject) {
 32                         
 33                         size_t len = strlen(attrs[i].value); // len = 7
 34                         if (len > 3) {
 35                             char name[len - 2]; // 新建一个长度 = len - 2 的name字符数组 长度为5
 36                             name[len - 3] = '';   // 设置最后一个字符为
 37                             memcpy(name, attrs[i].value + 2, len - 3); // copy USer 到name 中，
 38                            
 39                             // 获取name 的真实实体类型
 40                             _cls = objc_getClass(name);
 41                         }
 42                     }
 43                 }
 44             } break;
 45             case 'V': { // Instance variable
 46                 if (attrs[i].value) {
 47                     _ivarName = [NSString stringWithUTF8String:attrs[i].value];
 48                 }
 49             } break;
 50             case 'R': {
 51                 type |= YYEncodingTypePropertyReadonly;
 52             } break;
 53             case 'C': {
 54                 type |= YYEncodingTypePropertyCopy;
 55             } break;
 56             case '&': {
 57                 type |= YYEncodingTypePropertyRetain;
 58             } break;
 59             case 'N': {
 60                 type |= YYEncodingTypePropertyNonatomic;
 61             } break;
 62             case 'D': {
 63                 type |= YYEncodingTypePropertyDynamic;
 64             } break;
 65             case 'W': {
 66                 type |= YYEncodingTypePropertyWeak;
 67             } break;
 68             case 'G': { // getter 方法
 69                 type |= YYEncodingTypePropertyCustomGetter;
 70                 if (attrs[i].value) {
 71                     _getter = NSSelectorFromString([NSString stringWithUTF8String:attrs[i].value]);
 72                 }
 73             } break;
 74             case 'S': { // setter 方法
 75                 type |= YYEncodingTypePropertyCustomSetter;
 76                 if (attrs[i].value) {
 77                     _setter = NSSelectorFromString([NSString stringWithUTF8String:attrs[i].value]);
 78                 }
 79             } // break; commented for code coverage in next line
 80             default: break;
 81         }
 82     }
 83     if (attrs) {
 84         free(attrs);
 85         attrs = NULL;
 86     }
 87     
 88     _type = type;
 89     
 90     // 获取setter 和 getter 方法
 91     if (_name.length) {
 92         if (!_getter) {
 93             _getter = NSSelectorFromString(_name);
 94         }
 95         if (!_setter) {
 96             _setter = NSSelectorFromString([NSString stringWithFormat:@"set%@%@:", [_name substringToIndex:1].uppercaseString, [_name substringFromIndex:1]]);
 97         }
 98     }
 99     return self;
100 }






最后让我来看看打印结果




1  objc_property_t property = class_getProperty([YYWeiboStatus class], "user");
2     
3     YYClassPropertyInfo *propertyInfo = [[YYClassPropertyInfo alloc] initWithProperty:property];
4 
5     NSLog(@"%@",propertyInfo.typeEncoding);






1 2016-05-23 16:00:12.134 ModelBenchmark[12626:245778] @"YYWeiboUser"






1 typedef struct example {
2     int* aPint;
3     double  aDouble;
4     char *aString;
5     int  anInt;
6     BOOL isMan;
7     struct example *next;
8 } Example;






1 @property (nonatomic, assign) Example example;






1 2016-05-23 16:04:59.493 ModelBenchmark[12684:250528] {example=^id*iB^{example}}






1 objc_property_t property = class_getProperty([YYWeiboStatus class], "statusID");
2     
3     YYClassPropertyInfo *propertyInfo = [[YYClassPropertyInfo alloc] initWithProperty:property];
4 
5     NSLog(@"%@",propertyInfo.typeEncoding);






1 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




        

	      

	    

	  

	  

	    
      
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          原文地址：https://www.cnblogs.com/machao/p/5520367.html