objective-c运行时机制runtime，动态获取对象的属性和成员变量

- (NSString *)description {

NSMutableString *stringM = [NSMutableString stringWithFormat:@"\n<%@: %p>\n",self.class,self];

//获取本类的clas
Class cls = object_getClass(self);

//输出参数，获取本类(不包括父类)成员变量总数
unsigned int outCount = 0;

//遍历本身和父类,并排除NSObject
while (cls != NULL && cls != NSClassFromString(@"NSObject")) {

//返回成员变量的的指针数组
Ivar *ivars = class_copyIvarList(cls, &outCount);

for (int i = 0; i < outCount; i++) {
//拿到成员变量结构体指针
Ivar ivar = ivars[i];
//获得成员变量的名字
NSString *ivarNameKey = [NSString stringWithUTF8String:ivar_getName(ivar)];
//删除下划线(因为编译器自动为属性生成带_的成员变量)
if ([ivarNameKey hasPrefix:@"_"]) {
ivarNameKey = [ivarNameKey stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:@""];
}
//获取变量的值
id value = [self valueForKey:ivarNameKey];

[stringM appendString:[NSString stringWithFormat:@" %@ -> %@\n",ivarNameKey,value]];
}

//释放指针
free(ivars);

//去父类中找
cls = class_getSuperclass(cls);
}

return stringM;
}