ios - 无法使用 'fetch' 类型的参数列表调用 '(NSFetchRequest<NSFetchRequestResult>)'

Question

我创建了一个辅助函数来加载 NSManagedObject使用 Swift 3，支持 iOS 9.0+。

class func loadContext(entityName: String, fetchConfiguration: ((NSFetchRequest<NSManagedObject>) -> Void)?) -> AnyObject? {
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    // Fetch requested data
    let dataFetchRequest = NSFetchRequest<NSManagedObject>(entityName: entityName)

    // Configure the fetch request with user parameters
    if fetchConfiguration != nil {
        fetchConfiguration!(dataFetchRequest)
    }

    do {
        return try appDelegate.managedObjectContext.fetch(dataFetchRequest as! NSFetchRequest<NSFetchRequestResult>)
    } catch {
        print("Failed to fetch feed data, critical error: \(error)")
    }

    return nil
}

但是我收到以下错误:

Cannot invoke 'fetch' with an argument list of type '(NSFetchRequest<NSFetchRequestResult>)'

我还尝试了几种变体，例如 let dataFetchRequest = NSFetchRequest<NSFechRequestResult>(entityName: entityName)他们都遇到了同样的错误。

Answer 1

这已回答我的问题Swift 3/XCode 8 NSManagedObjectContext.fetch error .

XCode 提供的错误消息不正确。正确的解决方法是正确转换您的返回值和方法。

managedObjectContext.fetch()返回[Any] 。您需要进行三项更改。

1. class func loadContext(entityName: String, fetchConfiguration: ((NSFetchRequest<NSManagedObject>) -> Void)?) -> [NSManagedObject]? {
2. let dataFetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
3. return try appDelegate.managedObjectContext.fetch(dataFetchRequest) as? [NSManagedObject]

我已向 Apple 提交了错误报告 - https://openradar.appspot.com/radar?id=5049582866137088