ios - 类型 '(Class) -> () -> (Class)'的值没有成员 'variable'

let fetchedResultsController: NSFetchedResultsController = { () -> NSFetchedResultsController<NSFetchRequestResult> in
    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Message")
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: true)]
    fetchRequest.predicate = NSPredicate(format: "friend.name = %@", self.friend!.name!)
    let delegate = UIApplication.shared.delegate as! AppDelegate
    let context = delegate.persistentContainer.viewContext
    let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    return frc
}()

在显示以下行的位置:fetchRequest.predicate = NSPredicate(format: "friend.name = %@", self.friend!.name!)我收到错误:Value of type '(ChatLogController) -> () -> (ChatLogController)' has no member 'friend'因此，由于某种原因，它显然无法在我的类friend中找到ChatLogController，还是我错了？这就是我的猜测，因为它找不到friend作为self的成员。

这是friend变量，它在ChatLogController类的内部:

var friend: Friend?
{
    didSet
    {
        navigationItem.title = friend?.name

        messages = friend?.messages?.allObjects as? [Message]

        messages = messages?.sorted(by: {$0.date!.compare($1.date! as Date) == .orderedAscending})
    }
}

任何人都知道为什么我会收到此错误以及如何解决它？

编辑:我注意到，如果我从第一个代码段的第一行中删除() -> NSFetchedResultsController<NSFetchRequestResult> in，该错误消失了，但是反而出现了以下错误:Unable to infer complex closure return type; add explicit type to disambiguate

最佳答案

您已将friend声明为optional属性，该属性在fetchedResultsController的initialisation时尚未初始化，该属性是一个常量，因此会产生错误。要解决此问题，您可以使用lazy initialisation，这意味着



使fetchedResultsController属性变得懒惰，这将延迟对象的创建，直到需要它为止

lazy var fetchedResultsController: NSFetchedResultsController = { [unowned self] () -> NSFetchedResultsController<NSFetchRequestResult> in
    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Message")
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: true)]
    fetchRequest.predicate = NSPredicate(format: "friend.name = %@", self.friend!.name!)
    let delegate = UIApplication.shared.delegate as! AppDelegate
    let context = delegate.persistentContainer.viewContext
    let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    return frc
}()

关于ios - 类型 '(Class) -> () -> (Class)'的值没有成员 'variable'，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/50134350/