Learn about iOS open problems--member variables in a class what happens if you don't instantiate

@interface Person:nsobject

@property (noatonmic,copy) nsstring * name;

@end

A person class, name is a member variable of person

If a person is written as a member variable in a class

Self.person.name = @ "Zhangsan";

If you do not instantiate a person before, you are actually manipulating a null pointer

[Nil setname:@ "Zhangsan"]; This problem is not easy to detect because the null pointer message in OC is not error-prone, but if you put the person in the array, you will be prompted that you cannot add nil in the array.

Basic knowledge, but beginners are easy to overlook.