ios - 将 NSPersistentStoreResult 转换为数组

Question

您好，我在使用以下代码时遇到问题。具体来说，if let 语句给出了 Cast from NSPeristentStoreResult to unrelated type [Item] always fails 警告。我正在使用 Swift 3.01。

看起来这应该很容易做到。我关注的这本书是使用早期版本的 Swift 编写的。谢谢你的宽容。

func demo(){

let request = NSFetchRequest<Item>(entityName: "Item")

  do {
     if let items = try CDHelper.shared.context.execute(request) as? [Item] {
        for item in items {
           if let name = item.name {
              print("Fetched Managed Object = '\(name)'")
           }
        }
     }
  } catch {
     print("Error executing a fetch request: \(error)")
  }
 }

Answer 1

使用fetch()代替execute():

if let items = try CDHelper.shared.context.fetch(request)
...

或者在您的上下文中使用perform:

 CDHelper.shared.context.perform {
      let fetchRequest: NSFetchRequest<Item> = Item.fetchRequest()            
      let items = try! fetchRequest.execute() 
      for item in items {
           if let name = item.name {
                print("Fetched Managed Object = '\(name)'")
           }
      }
}