无法在Swift 3中实例化带有通用类型AnyObject的NSFetchedResultController [英] Unable to instantiate NSFetchedResultController with generic type AnyObject in Swift 3

问题描述

NSFetchedResultsController需要一个通用的类型参数，并且需要一个通用的类型参数。 AnyObject已经工作正常到现在。编译器抛出错误：

 类型AnyObject不符合协议'NSFetchRequestObject'
  

< img src =https://i.stack.imgur.com/0aIOg.pngalt =Screen shot>

让我额外混淆，如果你删除类型参数，XCode然后说：

 引用通用类型NSFetchedResultsController需要参数` 。>`
  

并帮助建议使用< AnyObject& /code>,循环重复。

这看起来非常像一个错误。 如果你看看 NSFetchedResultsController c>，可以清楚地看到它有一个名为 ResultType 的参数，它符合 NSFetchRequestResult 。所以你应该传递符合 NSFetchRequestResult 的类型。

因此，如果您查看 NSFetchRequestResult ，您可以看到它符合 NSObjectProtocol 。另外 NSDictionary ， NSManagedObject 和 NSManagedObjectID 符合 NSFetchRequestResult 。

  public protocol NSFetchRequestResult：NSObjectProtocol {
} 
 
扩展NSDictionary：NSFetchRequestResult {
} 
 
扩展NSManagedObject：NSFetchRequestResult {
} 
 
扩展NSManagedObjectID：NSFetchRequestResult {
 } 
  

所以很清楚，你应该传递一个类型从这三个 NSDictionary 或 NSManagedObject 或 NSManagedObjectID 。

像这样创建 NSFetchedResultsController 的实例。

  let resultsController：NSFetchedResultsController< NSManagedObject> ;! 
  

或像这样

  let resultsController：NSFetchedResultsController< NSManagedObjectID> ;! 
  

或像这样

  let resultsController：NSFetchedResultsController< NSDictionary> ;! 
  

I'm experimenting with CoreData in Swift 3 and have come up against a very bizarre circular compiler error in Xcode 8 beta.

NSFetchedResultsController needs a generic type parameter and AnyObject has worked fine up until now. The compiler throws the error:

Type 'AnyObject' does not conform to protocol 'NSFetchRequestObject'

To make me extra confused, if you delete the type parameter, XCode then says:

Reference to generic type NSFetchedResultsController requires argument in `<...>`

and helpfully suggests a fix using <AnyObject>....and the cycle repeats.

This looks very much like a bug. Any ideas before I report it?

解决方案

If you take a look into NSFetchedResultsController, you can clearly see that it has a parameter with name ResultType which conforms to NSFetchRequestResult. So you should pass a type which conforms to NSFetchRequestResult.

So if you take a look into NSFetchRequestResult, you can see that it conforms to NSObjectProtocol. Also NSDictionary, NSManagedObject and NSManagedObjectID conforms to NSFetchRequestResult.

public protocol NSFetchRequestResult : NSObjectProtocol {
}

extension NSDictionary : NSFetchRequestResult {
}

extension NSManagedObject : NSFetchRequestResult {
}

extension NSManagedObjectID : NSFetchRequestResult {
}

So it clear that you should pass a type from any of these three NSDictionary or NSManagedObject or NSManagedObjectID.

Create your instance of NSFetchedResultsController like this.

let resultsController : NSFetchedResultsController<NSManagedObject>!

or like this

 let resultsController : NSFetchedResultsController<NSManagedObjectID>!

or like this

let resultsController : NSFetchedResultsController<NSDictionary>!

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