使用核心数据实现枚举的最佳方式 [英] Best way to implement Enums with Core Data

问题描述

将Core Data实体绑定到枚举值的最佳方式是什么，以便能够为实体分配类型属性？换句话说，我有一个名为 Item 的实体，带有一个 itemType 属性，我想绑定到枚举，

What is the best way to bind Core Data entities to enum values so that I am able to assign a type property to the entity? In other words, I have an entity called Item with an itemType property that I want to be bound to an enum, what is the best way of going about this.

推荐答案

如果要限制值，您必须创建自定义访问器到枚举。因此，您首先要声明一个枚举，例如：

You'll have to create custom accessors if you want to restrict the values to an enum. So, first you'd declare an enum, like so:

typedef enum {
    kPaymentFrequencyOneOff = 0,
    kPaymentFrequencyYearly = 1,
    kPaymentFrequencyMonthly = 2,
    kPaymentFrequencyWeekly = 3
} PaymentFrequency;

然后，声明属性的getter和setter。这是一个坏主意，重写现有的，因为标准访问器期望一个NSNumber对象而不是标量类型，如果绑定或KVO系统中的任何东西尝试和访问您的值，你会遇到麻烦。

Then, declare getters and setters for your property. It's a bad idea to override the existing ones, since the standard accessors expect an NSNumber object rather than a scalar type, and you'll run into trouble if anything in the bindings or KVO systems try and access your value.

- (PaymentFrequency)itemTypeRaw {
    return (PaymentFrequency)[[self itemType] intValue];
}

- (void)setItemTypeRaw:(PaymentFrequency)type {
    [self setItemType:[NSNumber numberWithInt:type]];
}

最后，您应该实现 + keyPathsForValuesAffecting& ，因此当itemType更改时，您可以获取itemTypeRaw的KVO通知。

Finally, you should implement + keyPathsForValuesAffecting<Key> so you get KVO notifications for itemTypeRaw when itemType changes.

+ (NSSet *)keyPathsForValuesAffectingItemTypeRaw {
    return [NSSet setWithObject:@"itemType"];
}

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