What is the underlying structure of a Category?

Balance:

Let’s start by creating a class

@interface CTTestClass : NSObject
@end
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Then create a category and add: – methods, + methods, protocols, attributes

@interface CTTestClass (Test)<NSCopying,NSCoding>

-(void)test1;

@property (assign, nonatomic) int weight;

@property (assign, nonatomic) double height;

@end
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@implementation CTTestClass (Test)

-(void)test1{
    
}

+(void)test2{
    
}

@end
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Then, the feature begins.

We open the command line, go to the code folder, and type:

Cxcrun-sdk iphoneOS clang -arch – rerewrite -objc CTTestClass+ test. m; ctestClass + test. m; ctestClass + test. m; ctestClass + test. m; ctestClass + test. m; ctestClass + test. m;

The compiler looks like this:

! [img1] (/ Users/CCT Mobile Documents/com/Library/apple CloudDocs/markDown/imgs/Category, rounding bottom – 1 / img1. PNG)

Don’t panic, let’s search: _category_t

You see a structure like this:

struct _category_t {
	const char *name;
	struct _class_t *cls;
	const struct _method_list_t *instance_methods;
	const struct _method_list_t *class_methods;
	const struct _protocol_list_t *protocols;
	const struct _prop_list_t *properties;
};
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Yeah, that’s it, the real structure of a Category, is this thing.

Think by name,

Name is a class name, CLS is a class, instance_methods is an object method, class_methods is a class method, protocols is a protocol, and properties is a property. So let’s verify that there are these things in the classification we just created. Let’s look for the underlying implementation.

Continue searching: _category_t

You can see this thing right here

static struct _category_t _OBJC_The $_CATEGORY_CTTestClass_The $_Test __attribute__ ((used.section(" __DATA, __objc_const"))) = 
{
	"CTTestClass".0.// &OBJC_CLASS_$_CTTestClass,
	(const struct _method_list_t *)&_OBJC_$_CATEGORY_INSTANCE_METHODS_CTTestClass_$_Test,
	(const struct _method_list_t *)&_OBJC_$_CATEGORY_CLASS_METHODS_CTTestClass_$_Test,
	(const struct _protocol_list_t *)&_OBJC_CATEGORY_PROTOCOLS_$_CTTestClass_$_Test,
	(const struct _prop_list_t *)&_OBJC_$_PROP_LIST_CTTestClass_$_Test,
};
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This is a _category_T structure named _OBJC_$_CATEGORY_CTTestClass_$_Test

If we look at what it says,

Const char *name in _category_t;

The second item: 0, followed by a comment, which needs no explanation, is the CTTestClass we created

The third: (const struct _method_list_t *) &_objc_ $_CATEGORY_INSTANCE_METHODS_CTTestClass_$_Test _INSTANCE_METHODS_, const struct _method_list_t *instance_methods in _category_t

Const struct _PROTOCOL_LIST_t *protocols from _category_t

Struct _protocol_LIST_t *properties const struct _protocol_T *properties