"Learning Notes", "OC Language" class method

1. Basic Concepts
A method that can be executed directly with the class name (the class itself occupies storage space in memory with a list of Class \ Object methods)

2. Comparison of class methods and Object methods
1> Object Methods
Start with minus sign-
Only objects can be called, no object, and this method cannot be executed at all.
Object methods can access instance variables (member variables)

2> class method
Start with a plus + +
Can only be called with the class name, the object cannot be called
Instance variables (member variables) cannot be accessed in a class method
Use cases: When you do not need to access member variables, try to use the class method
Class methods and object methods can have the same name

3. Code

1 #import<Foundation/Foundation.h>2 /*3 Object Methods4 1> minus-Start5 2> can only be called by an object6 a member variable (instance variable) that can access the current object in the 3> object method7  8 class Method9 1> Plus + startTen 2> can only be called by Class (name) One member variables (instance variables) cannot be accessed in the 3> class method A   -   - the benefits and applications of class methods the 1> is not dependent on the object, the execution efficiency is high - 2> can use class method, try to use class method - 3> Occasions: You can change to a class method when you do not need to use a member variable inside a method -   + you can allow class methods and object methods to have the same name -  */ +  A  at @interfacePerson:nsobject - { -     intAge ; - } -  - //class methods start with A + in+ (void) Printclassname; -  to- (void) test; ++ (void) test; -  the @end *  $ @implementation PersonPanax Notoginseng  -+ (void) Printclassname the { +     //error:instance variable ' age ' accessed in class method A     //instance variable age cannot be accessed in a class method the     //NSLog (@ "This class is called person-%d", age); + } -  $- (void) Test $ { -NSLog (@"111-%d", age); -      the     //[Person test]; - }Wuyi  the+ (void) Test - { Wu     //will trigger a dead loop . -     //[Person test]; About      $NSLog (@"333"); -      -     //will trigger a dead loop . - ///[person test]; A } +  the @end -  $ intMain () the { the     //[Person Printclassname]; the      the [Person test]; -      in     //Person *p = [person new]; the     //[P test]; the      About     /* the -[person Printclassname]: Unrecognized selector sent to instance 0x7fa520c0b370 the      */ the     //The system will assume that the printclassname called now is an object method +     //[P printclassname]; -      the     return 0;Bayi}

"Learning Notes", "OC Language" class method