这里记录一下自己在学习Runtime的心得，这里主要记录的是Ivar 和 Property 在获取类的属性和实例变量时候的区别。
class_copyIvarList 可以获取class的实例变量，包括属性，但是属性前加一个“ _ ”下划线。
class_copyPropertyList只会获取class的属性。

Ivar

定义：

   typedef struct objc_ivar *Ivar

常用方法：

   Ivar *class_copyIvarList(Class cls, unsigned int *outCount)

   const char *ivar_getTypeEncoding(Ivar v) 
   const char *ivar_getName(Ivar v) 

Property

定义：

    typedef struct objc_property *objc_property_t;

常用方法：

 const char *property_getName(objc_property_t property) 
 const char *property_getAttributes(objc_property_t property) 
 objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)

例子：

  #import "RSBaseListViewController.h"
  @interface MyOrderStatusListViewController : RSBaseListViewController
  @property (nonatomic, strong) NSString *orderStatus;
  @end

  #import "objc/runtime.h"
  @interface MyOrderStatusListViewController ()
  {
      NSMutableArray *dataArray;
  }
  @end

-(void)loadData
{
    unsigned int ivarNum = 0;
    Ivar *ivarList = class_copyIvarList([self class], &ivarNum);
    for (int i = 0; i < ivarNum; i++) {
        Ivar myIvar = ivarList[i];
        const char *type = ivar_getTypeEncoding(myIvar);
        NSString *stringType = [NSString stringWithCString:type encoding:NSUTF8StringEncoding];
        NSLog(@"type %@", stringType);
    
        const char *name = ivar_getName(myIvar);
        NSString *stringName = [NSString stringWithCString:name encoding:NSUTF8StringEncoding];
        NSLog(@"name %@", stringName);
    }

    unsigned int propertyNum = 0;
    objc_property_t *propertyList = class_copyPropertyList([self class], &propertyNum);
    for (int j = 0; j < propertyNum; j++) {
        objc_property_t myProperty = propertyList[j];
        const char *propertyName = property_getName(myProperty);
        NSString *stringPropertyName = [NSString stringWithCString:propertyName encoding:NSUTF8StringEncoding];
        NSLog(@"property Name %@", stringPropertyName);
    
        const char *propertyAttribute = property_getAttributes(myProperty);
        NSLog(@"property Attribute %s \n", propertyAttribute);
    }
}

cmd 输出

 [2508:1547221] type @"NSMutableArray"
 [2508:1547221] name dataArray
 [2508:1547221] type @"NSString"
 [2508:1547221] name _orderStatus
 [2508:1547221] property Name orderStatus
 [2508:1547221] property Attribute T@"NSString",&,N,V_orderStatus 

对比头文件，RSBaseListViewController.h里面定义了 orderStatus，属性 RSBaseListViewController.m 里面定义了 dataArray 实例变量，可以看出来，Ivar可以获取属性和实例变量，并且属性会有一个"_", Property可以获取我们定义的时候的参数。

学到这个东西可以干嘛了呢？

自动归档

@interface Person:NSObject
@property(nonautomic, strong) NSString *name;
@property(nonautomic, strong) NSString *sex;
@end

@implementation
-(void)encodeWithCoder:(NSCoder *)encoder
{
  unsigned int count = 0;
  Ivar *ivar = class_copyIvarList([self class] , &count);
  for(int i = 0; i < count ; i++){
       Ivar myVar = ivar[i];
       const char *name = ivar_getName(myVar);
       NSString *stringName = [NSString stringWithUTF8String:name];
       [encode encodeObject:[self valueForKeyPath:stringName] forKey:stringName];
  }
}
@end

自动实现NSCoping协议

- (id)copyWithZone:(nullable NSZone *)zone
{
    
    UserEntity *entity = [[self class]allocWithZone:zone];
    unsigned int propertyNum;
    objc_property_t * propertys = class_copyPropertyList([self class], &propertyNum);
    for (int i = 0; i < propertyNum; i++) {
        objc_property_t property = propertys[i];
        const char * propertyChar = property_getName(property);
        NSString *propertyName = [NSString stringWithUTF8String:propertyChar];
        id value = [self valueForKeyPath:propertyName];
        if (value) {
            [entity setValue:[self valueForKeyPath:propertyName] forKeyPath:propertyName];
        }
    }
    free(propertys);
   
    return entity;
}