(Objective-C) 通过关联对象给分类添加成员变量

• 使用给定的键和关联策略为指定对象设置关联值

objc_setAssociatedObject(id _Nonnull object, const void * _Nonnull key,
                         id _Nullable value, objc_AssociationPolicy policy)
    OBJC_AVAILABLE(10.6, 3.1, 9.0, 1.0, 2.0);

• 返回与给定键的指定对象关联的值

objc_getAssociatedObject(id _Nonnull object, const void * _Nonnull key)
    OBJC_AVAILABLE(10.6, 3.1, 9.0, 1.0, 2.0);

• Example

// set method
- (void)setTestName:(NSString *)testName {
    objc_setAssociatedObject(self, @selector(testName), testName, OBJC_ASSOCIATION_COPY_NONATOMIC);
}

// get method
- (NSString *)testName {
    return  objc_getAssociatedObject(self, _cmd);
}

// dealloc
- (void)dealloc {
    objc_removeAssociatedObjects(self);
}

objc_AssociationPolicy

• OBJC_ASSOCIATION_ASSIGN (assign)
• OBJC_ASSOCIATION_RETAIN_NONATOMIC (strong，nonatomic)
• OBJC_ASSOCIATION_COPY_NONATOMIC (copy, nonatomic)
• OBJC_ASSOCIATION_RETAIN (strong, atomic)
• OBJC_ASSOCIATION_COPY (copy, atomic)