ios - Swift 2/Xcode 7.0 - 条件绑定(bind)的初始值设定项必须具有可选类型而不是 'nsmanagedobjectcontext'

Question

刚刚从 Xcode 6.4 更新到 Xcode 7.0。在我的项目中，我现在遇到了一个错误，我整晚都在尝试解决这个错误，但没有成功。

错误信息是:条件绑定(bind)的初始化器必须有可选类型而不是'nsmanagedobjectcontext'

错误出现在 if let managedObjectContext = self.managedObjectContext { 在下面的代码行中两次

func preloadData () {
    // Retrieve data from the source file
    if let contentsOfURL = NSBundle.mainBundle().URLForResource("listofdata", withExtension: "csv") {

        // Remove all the items before preloading
        removeData()

        var error:NSError?
        if let items = parseCSV(contentsOfURL, encoding: NSUTF8StringEncoding, error: &error) {
            // Preload the items
            if let managedObjectContext = self.managedObjectContext {
                for item in items {
                    let listOfItem = NSEntityDescription.insertNewObjectForEntityForName("ListOfItem", inManagedObjectContext: managedObjectContext) as! ListOfItem
                    listOfItem.name = item.name
                    listOfItem.address = item.address
                    listOfItem.phone = item.phone

                    if managedObjectContext.save(&error) != true {
                        print("insert error: \(error!.localizedDescription)")
                    }
                }
            }
        }
    }
}

func removeData () {
    // Remove the existing items
    if let managedObjectContext = self.managedObjectContext {
        let fetchRequest = NSFetchRequest(entityName: "ListOfItem")
        var e: NSError?
        let listOfItems = managedObjectContext.executeFetchRequest(fetchRequest, error: &e) as! [ListOfItem]

        if e != nil {
            print("Failed to retrieve record: \(e!.localizedDescription)")

        } else {

            for listOfItem in listOfItems {
                managedObjectContext.deleteObject(listOfItem)
            }
        }
    }
}

感谢所有帮助!谢谢!

更新:

更新后的代码看起来像这样，但是在第一个函数 preloadData 中仍然有这两个错误:

1. 调用中缺少参数“error”的参数

2. 条件绑定(bind)的初始化器必须是 Optional 类型，而不是 'NSManagedObjectContext'

   func preloadData () {
   // Retrieve data from the source file
   if let contentsOfURL = NSBundle.mainBundle().URLForResource("listofdata", withExtension: "csv") {
   
       // Remove all the menu items before preloading
       removeData()
   
       do {
           let items = try parseCSV(contentsOfURL, encoding: NSUTF8StringEncoding)
           // Preload the items
           if let managedObjectContext = self.managedObjectContext {
               for item in items {
                   let listOfItem = NSEntityDescription.insertNewObjectForEntityForName("ListOfItem", inManagedObjectContext: managedObjectContext) as! ListOfItem
                   listOfItem.name = item.name
                   listOfItem.address = item.address
                   listOfItem.phone = item.phone
   
                   if managedObjectContext.save() != true {
                       print("insert error: \(error.localizedDescription)")
                   }
               }
           }
       } catch let error as NSError {
           print("insert error: \(error.localizedDescription)")
       }
   }
   

这个函数显示没有错误

func removeData () {
    // Remove the existing items
    let fetchRequest = NSFetchRequest(entityName: "ListOfItem")

    do {
        let listOfItems = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [ListOfItem]
        for listOfItem in listOfItems {
            self.managedObjectContext.deleteObject(listOfItem)
        }
    }
    catch let error as NSError {
        print("Failed to retrieve record: \(error.localizedDescription)")
    }

有什么帮助吗？谢谢!

Answer 1

在 Swift 2 中，Core Data 模板将 AppDelegate 中的属性 managedObjectContext 实现为非可选属性。可能更新程序相应地更改了实现。

好处是不再需要可选绑定(bind)，但是您必须考虑新的错误处理，例如

func removeData () {
  let fetchRequest = NSFetchRequest(entityName: "ListOfItem")

  do {
    let listOfItems = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [ListOfItem]
    for listOfItem in listOfItems {
       self.managedObjectContext.deleteObject(listOfItem)
     }
   }
   catch let error as NSError {
     print("Failed to retrieve record: \(error.localizedDescription)")
   }
}