ios - if let 语句错误

Question

我正在尝试使用 coreData 构建一个待办事项列表，我的目标是，如果用户尝试仅单击“添加”按钮而不在文本字段中输入任何文本，则会弹出错误通知。我目前可以使用弹出通知，但是一旦我关闭通知，然后将文本添加到文本字段并单击“添加”按钮，应用程序就会崩溃。

@IBAction func addBtnTaskPressed(_ sender: Any) {
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    let task = Task(context: context)

    //have to add an if let here.
    if let text = textField.text, !text.isEmpty{
        task.name = textField.text
        //save data to coredata
        (UIApplication.shared.delegate as! AppDelegate).saveContext()
    } else {
    let alert = UIAlertController(title: "Error:", message: "Cannot Add Empty Task", preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "Continue", style: UIAlertActionStyle.default, handler: nil))
    self.present(alert, animated: true, completion: nil)
    }

}

Answer 1

我认为您没有正确保存 coreData。试试这个(不过我还没有测试过)

@IBAction func addBtnTaskPressed(_ sender: Any) {
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.managedObjectContext
    let entity =  NSEntityDescription.entity(forEntityName: "Task", in: context)
    let task = NSManagedObject(entity: entity!, insertInto: context) as! Task


    //have to add an if let here.
    if let text = textField.text, !text.isEmpty{
    task.name = textField.text
    //save data to coredata
       do {
           try context.save()
           print("saved!")
       } catch let error as NSError  {
        print("Could not save \(error), \(error.userInfo)")
       }        
    } else {
    let alert = UIAlertController(title: "Error:", message: "Cannot Add Empty     Task", preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "Continue", style: UIAlertActionStyle.default, handler: nil))
    self.present(alert, animated: true, completion: nil)
  }
}