How to store a NSManagedObjectID persistently?
为避免成为 XY 问题，这里有一些背景：
我的应用程序允许用户创建和保存很多设置，有点像 Xcode 的字体和颜色选择器：
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NSData(contentsOfURL: selectedOption!.objectID.URIRepresentation())
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但是初始化程序以某种方式失败了。
现在我意识到这是一个愚蠢的想法，因为即使我可以将其转换为
根据this question，OP似乎能够存储对象id：
I store the selected theme objectID in NSUserDefaults so that when the app restarts, the selected theme will still be intact.
我该怎么做呢？
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public func setURL(url: NSURL?, forKey defaultName: String)
public func URLForKey(defaultName: String) -> NSURL? |
允许存储和检索
通过
被透明地处理。来自文档：
When an NSURL is stored using
-[NSUserDefaults setURL:forKey:] , some adjustments are made:Any non-file URL is written by calling +[NSKeyedArchiver archivedDataWithRootObject:] using the NSURL instance as the root
object.… When an NSURL is read using
-[NSUserDefaults URLForKey:] , the following logic is used:If the value for the key is an NSData, the NSData is used as the argument to +[NSKeyedUnarchiver unarchiveObjectWithData:] . If the NSData can be unarchived as an NSURL, the NSURL is returned otherwise nil is returned.…
所以保存被管理对象 ID 只是简单地做为
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NSUserDefaults.standardUserDefaults().setURL(object.objectID.URIRepresentation(),
forKey:"selected") |
并检索对象 ID 和对象，例如：
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if let url = NSUserDefaults.standardUserDefaults().URLForKey("selected"), let oid = context.persistentStoreCoordinator!.managedObjectIDForURIRepresentation(url), let object = try? context.existingObjectWithID(oid) { print(object) |
有关保存所选设置的替代方法，请参阅上面的评论。
原创文章，作者：ItWorker，如若转载，请注明出处：https://blog.ytso.com/268633.html