This is the sixth day of my participation in the November Gwen Challenge. Check out the event details: The last Gwen Challenge 2021

Today the sun is just, the breeze is not dry ~

What a day for talking ~

Today we’re going to chatter about objects in iOS

Speaking of objects, there are several types of objects in iOS

Three types of objects in iOS

  1. Instance object
  2. Class object (class)
  3. Metaclass objects (meta-classes)

For example, at this point we have two classic two classes,Persion inherits from NSObject and Student inherits from Persion

@interface Persion : NSObject @property (nonatomic, copy) NSString *name; @property (nonatomic, assign) int age; @end @interface Student: Persion @property (nonatomic, copy) NSString *teacher; @endCopy the code

Instance objects

Instance objects are the classes we generate by alloc init, for example:

Student *s = [[Student alloc] init]; // Instance objectCopy the code

So what do instance objects store in memory?

  1. isaPointer to the
  2. Member variables

The isa pointer points to the class object of the instance object, and the member variables are the property variables of the instance object

In the current example, the isa pointer points to the Student class and the member variable is just teacher

Class object

Class objects are what we call classes and can be obtained using the class method, or object_getClass().

Class objects mainly store:

  1. isaPointer to the
  2. superClassPointer to the
  3. Class attribute information (@Property) Object method information of the class
  4. Class protocol information, class member variables information

Among them:

  • isaPointers to metaclass objects
  • superClassPointer to the superclass object, hereStudentThe superclass of theta is thetaPersion
  • Class attribute information refers to the attribute information of the instance object, here refers toteacherThe information of
  • The object method information of a class is instance method information
  • The protocol information of a class is the protocol information of the class
  • The member variable information of a class is the member variable of an object

Yuan class object

Each class object has a metaclass object corresponding to it in memory, which can be obtained via object_getClass()

Note that the metaclass object is obtained via object_getClass () and the parameter is passed as a class object

So what’s in a metaclass object:

  1. isaPointer to the
  2. superClassPointer to the
  3. Class method information for a class

Among them:

  • The ISA pointer points to the root metaclass, which in this case points to nsobject’s metaclass
  • The superClass pointer points to the superClass’s metaclass, which in this case points to Persion’s metaclass

Here’s a classic picture:

The SubClass is Student, the SuperClass is Persion, and the Root class is NSObject

That’s the introduction to objects in iOS