iOS Category/分类添加成员变量

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注意: 分类是不能直接添加成员变量到分类中的,但是可以通过关联对象添加成员变量

关联对象主要使用下面的 api

添加关联对象:

//关联对象
//object: 需要关联的对象
//key: 关联的 key  用来取值
//value: 关联的值
/*policy:  关联策略, 就是给属性增加 copy,strong,assgin. 一样的用法.具体对应请参考图1
typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
    OBJC_ASSOCIATION_ASSIGN = 0,    /**< Specifies a weak reference to the associated object. */
    OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_COPY_NONATOMIC = 3,   /**< Specifies that the associated object is copied. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_RETAIN = 01401,       /**< Specifies a strong reference to the associated object.
                                            *   The association is made atomically. */
    OBJC_ASSOCIATION_COPY = 01403          /**< Specifies that the associated object is copied.
                                            *   The association is made atomically. */
};
*/
void objc_setAssociatedObject(id object, const void * key,
                                id value, objc_AssociationPolicy policy)

//获得关联对象
//object :关联的对象
//key: 关联的key
id objc_getAssociatedObject(id object, const void * key)
//移除所有的关联对象
//object: 关联的对象
void objc_removeAssociatedObjects(id object)

图 1:

关联 key 的常规用法

static void *MyKey = &MyKey;
objc_setAssociatedObject(obj, MyKey, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj, MyKey)

static char MyKey;
objc_setAssociatedObject(obj, &MyKey, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj, &MyKey)

使用属性名作为key
objc_setAssociatedObject(obj, @"property", value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
objc_getAssociatedObject(obj, @"property");

使用get方法的@selecor作为key
objc_setAssociatedObject(obj, @selector(getter), value, OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj, @selector(getter))

如何使用

import UIKit

class Person: NSObject {
      
}

extension Person {
    var name: String {
        get {
            return objc_getAssociatedObject(self, "name") as! String
        }
        set {
            objc_setAssociatedObject(self, "name", newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_COPY_NONATOMIC)
        }
    }
    
}

let model = Person()
model.name = "测试"
print("name= \(model.name)")