如何在核心数据中存储 CGRect 和其他东西

How to store CGRect and other things in core data(如何在核心数据中存储 CGRect 和其他东西)

问题描述

我在使用 coredata 时遇到了一些初期问题，但如果有人可以向我解释一些简单的案例，我觉得这对我来说很清楚.

I'm having a few teething problems with coredata, but feel it would clear things up for me greatly if someone could explain some simple cases to me.

我想将我的模型放入 coredata，并且在最简单的情况下利用撤消/重做.问题是，我看到的所有示例都倾向于存储字符串或整数.如果我有一个想要在核心数据中实现的类(一个虚构的例子)怎么办:

I want to put my model into coredata, and at a most simple case take advantage of undo/redo. Thing is, all the examples I see tend to store either strings or integers. What if I have a class as follows that I wanted to implement in core data (a made up example):

@interface Badge : NSObject {

NSString *textForBadge;
int      badgeValue;
UIColor  *color;
CGRect    rect;
NSMutableArray *awards; // this would be a list of 'Category' - another custom class
}

这些都是当场编造出来的，但每一个都凸显了一个困惑

如我所见，我将打开 .xcdatamodel 并添加一个名为Badge"的新实体，它是一个 NSManagedObject.然后，我为 textForBadge 添加一个 String 类型的属性.到现在为止还挺好.我为 badgeValue 做了类似的事情，但后来来到 UIColor 和 CGRect 我有点难过，因为没有这些属性.我是否应该创建一个实体来表示每个整数(即具有四个属性 x,y,w,h 的 Rect 实体)?然后每次都用这些整数填充一个 CGRect ?UIColor 也一样?

As I see it, I would open the .xcdatamodel and add a new Entity caled 'Badge', which would be an NSManagedObject. I then add a property for textForBadge of type String. So far so good. I do somthing similar for badgeValue, but then come to the UIColor and CGRect and I'm a bit stumped, since there isn't a property for those. Am I supposed to create an entity to represent each (i.e a Rect entity that has four properties x,y,w,h) that are ints? Then populate a CGRect with these ints each time? Ditto for the UIColor?

最后，我来看看我的奖项列表.如果这些是指向代表奖项的多个对象的指针列表，它们可能包含图像、颜色、文本等.我​​假设 award 将再次成为我必须设计的实体，而不是Badge 存储一个数组我会从它到 Award 类有一对多的关系.

Finally, I come to my list of awards. If these are a list of pointers to a number of objects representing an award they might contain an image, a colour, text etc. I assume that award would again be an entity I have to design and rather than Badge storing an array I would have a 1 to many relationship from it to the Award class.

我做对了这件事，还是朝着相反的方向前进?我看到的所有示例都在像 String 或 int 这样的普通对象上运行，所以想确保在实现一堆东西之前我脑子里有这个.

Am I getting any of this right, or going in the compete opposite direction? All the examples I see operate on vanilla objects like String or int so want to make sure I have this right in my head before implementing a bunch of stuff.

亲切的问候，

布林

推荐答案

这是相关文档:http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdNSAttributes.html 但本质上，你有为 Core Data 提供一种在你的非标准属性和它可以存储的东西之间进行转换的方法.有两种方法可以做到这一点.要么使用可转换属性和值转换器，要么使用瞬态属性并仅在要保存托管对象上下文时进行转换.

This is the relevant documentation: http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdNSAttributes.html but essentially, you have to provide a way for Core Data to translate between your non-standard properties and the kinds of things it can store. There are two ways to do it. Either use transformable attributes and value transformers, or use transient properties and do the conversion only when the managed object context is going to be saved.

我认为在大多数情况下，您所描述的内容(定义自定义实体以存储类似 CGRect 的组件)是多余的.

I think in most cases, what you describe (defining custom entities to store the components of something like a CGRect) is overkill.

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