ios - 谓词不适用于 CoreData - Swift 4

Question

我正在尝试加载索引为 1 的名称，但它不起作用(CollectionView 为空)。

核心数据:

加载数据:

guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }

let managedContext = appDelegate.persistentContainer.viewContext
let fetchRequestTag = NSFetchRequest<NSManagedObject>(entityName: "Tag")
let PreValue = 1
let predicate = NSPredicate(format: "index == %i", PreValue)
fetchRequestTag.predicate = predicate

do {
   tagItems = try managedContext.fetch(fetchRequestTag)
} catch let error as NSError {
   print("Could not fetch. \(error), \(error.userInfo)")
}

TagCollectionView.reloadData()
TagCollectionView.selectItem(at: NSIndexPath(item: 0, section: 0) as IndexPath, animated: false, scrollPosition: [])

for data in tagItems {
   print("\(data.value(forKey: "name") as! String as Any), \(NSKeyedUnarchiver.unarchiveObject(with: data.value(forKeyPath: "index") as! Data) as! Int)")
}

Answer 1

属性类型和谓词类型不匹配。

Transformable因为 index 的类型无论如何都是荒谬的。将属性类型设置为 Int32 , 或者如果只有 0和 1索引甚至到 Bool .