Class structure Analysis (PART 1)

Class structure analysis

Isa pointing

So we have an object LGPerson that inherits NSObject and let’s print out isa

    // NSObject instance object
    LGPerson *object1 = [LGPerson alloc];
    / / NSObject class
    Class class = object_getClass(object1);
    / / NSObject metaclass
    Class metaClass = object_getClass(class);
    // NSObject root metaclass
    Class rootMetaClass = object_getClass(metaClass);
    // NSObject Root metaclass
    Class rootRootMetaClass = object_getClass(rootMetaClass);
    NSLog(@"\n%p instance object \n%p class \n%p metaclass \n%p root metaclass \n%p root metaclass",object1,class.metaClass.rootMetaClass.rootRootMetaClass);
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Where isa is directed: instance object -> class -> metaclass -> root metaclass -> root metaclass

As shown below

If 0x100008240 is a metaclass, open MacOView and search symbloTable for class 0x100008240

Metaclasses are generated automatically at compile time and are not made available for external use.

Inheritance relationships

Let’s look at inheritance:

Class inheritance:

/ / LGPerson metaclass
    Class pMetaClass = object_getClass(LGPerson.class);
    Class psuperClass = class_getSuperclass(pMetaClass);
    NSLog(@"% @ - % @",pMetaClass,psuperClass);
    LGPerson - NSObject
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Inheritance of metaclasses

Metaclasses are classes, metaclasses have inheritance, so let’s write a LGTeacher that inherits from a LGPerson

@interface LGTeacher : LGPerson

@end
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    Class tMetaClass = object_getClass(LGTeacher.class);
    Class tsuperClass = class_getSuperclass(tMetaClass);
    Class tsuperClass01 = class_getSuperclass(tsuperClass);
    Class tsuperClass00 = class_getSuperclass(tsuperClass01);
    Class tsuperClass000 = class_getSuperclass(tsuperClass00);
  NSLog(@"\ n % @ % p metaclass \ n % @ - father metaclass \ n % p % @ - $% p root class \ % n % @ - p root metaclass super \ % n % @ - p",tMetaClass, tMetaClass, tsuperClass,tsuperClass, tsuperClass01,tsuperClass01, tsuperClass00, tsuperClass00, tsuperClass000,tsuperClass000);

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The results are as followsAs you can see from the print, the parent of the root metaclass is NSObject, and Superclass(NULL)–0x0 validates the root class special case

 // NSObject root class special case
    Class nsuperClass = class_getSuperclass(NSObject.class);
    NSLog(@"%@ - %p",nsuperClass,nsuperClass);
     (null)--0x0
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// Root metaclass -> NSObject
    Class rnsuperClass = class_getSuperclass(tsuperClass01);
    NSLog(@"%@ - %p",rnsuperClass,rnsuperClass);
    NSObject - 0x7fff808b0388
    
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The inheritance diagram is as follows:

The overall process is as follows: