objective-c - 在Obj-C中实例方法和类方法的区别是什么？

Question

实例方法，即需要实例化对象调用的方法。
类方法，即类直接调用的方法。

我不明白什么场合用类方法，什么场合用实例方法。两者相比较真正的优势和劣势又是什么？

Answer 1

Class methods are generally used to provide standardized processing; instance methods are generally used to provide personalized processing (binding to specific instances).

Answer 2

There should be no such thing as advantages and disadvantages.

• If a method has the same input parameters, the output will be affected by the instance variables of different object instances. Generally, it should be written as an instance method.

• If the input parameters are the same but are not affected by instance variables (static does not count as instance variables), you can write a class method and give it to the class to call. For example

- (NSString *)getCertainString
{
    return @"The string."
}

You can write this kind of ghost as an instance method, but not only will one be instantiated/released every time it is called, it will also affect code reading.

• Class methods are more common in singleton mode and factory mode. This class in the singleton mode program has only one instance; the factory mode produces different instances and returns them based on the parameters.

Answer 3

There is no distinction between the methods, they are just for convenience of use. If you have to distinguish, the following should be considered

Disadvantages of class methods: In class methods, self represents a class, not a class object, so in a class method you cannot use self. to call attributes, nor can you call instance methods of this class.
Advantages of class methods: The call is simple, no need to create objects