Objective-C

/** 原文件 */

// Person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;

@end

// Person.m

#import "Person.h"

@implementation Person

- (instancetype)init {

    if (self = [super init]) {

        _name = @"";

        NSLog(@"%@", [self class]); // Person

        NSLog(@"%@", [super class]); // Person

    }

    return self;

}

- (void)dealloc {

    NSLog(@"Call dealloc in Person.m");

}

@end

/** Category文件*/

// Person+Category.h

#import "Person.h"

@interface Person (Category)

// 添加属性address

@property (nonatomic, copy) NSString *address;

@end

// Person+Category.m

#import "Person+Category.h"

#import <objc/runtime.h>

@implementation Person (Category)

static void *addressKey = &addressKey;

#pragma mark - OC 在Category关联属性

- (void)setAddress:(NSString *)address {

    objc_setAssociatedObject(self, &addressKey, address, OBJC_ASSOCIATION_COPY_NONATOMIC);

}

- (NSString *)address {

    return objc_getAssociatedObject(self, &addressKey);

}

/** 在category里面执行dealloc方法后，Person类文件里的dealloc会不执行 */

- (void)dealloc {

    objc_removeAssociatedObjects(self);

    NSLog(@"remove associated");

}

@end

// test

#import "Person+Category.h"

Person *p = [Person new];

p.name = @"xiaoMing";

p.address = @"gz";

NSLog(@"name is: %@, address is: %@", p.name, p.address);

Swift

// .swift文件

import Cocoa

class Car {

    var name = ""

}

private var priceKey: Void?

extension Car {

    /// car's price

    var price: Double? {

        get {

            return objc_getAssociatedObject(self, &priceKey) as? Double

        }

        set {

                objc_setAssociatedObject(self, &priceKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)

        }

    }

}

let c1 = Car()

c1.name = "su"

c1.price = 110000.1

print("c1's name is: \(c1.name) and price is: \(c1.price!)")