swift - 尝试从核心数据加载时在 swift 中发现 nil

Question

代码之前 - 用于传入新数据 ...

else
{
    DispatchQueue.main.async
    {
            let fetchRequest:NSFetchRequest<Identity> = Identity.fetchRequest()
            do {
                self.identities = try DatabaseController.getContext().fetch(fetchRequest)
                for identity in self.identities as [Identity]
                {
                    if identity.id == self.transferedId
                    {
                    //name
                    self.navigationController?.navigationBar.topItem?.title = identity.pName
                    self.nameField.text = identity.pName

                    //birth
                    let dateFormatter = DateFormatter()
                    dateFormatter.dateFormat = "dd-MM-yyyy"
                    var dateString = dateFormatter.string(from:identity.birthDate! as Date)
                    self.birthField.text = dateString

                    //modified
                    dateString = dateFormatter.string(from:identity.lastModified! as Date)
                    self.modified.text = "Modified on "+dateString
                    }
                }
            }
            catch
            {
                print("Error fetchRequest in ViewWillApper: \(error)")
            }
    }

}

... 它不会加载错误的窗口。 问题是 - 当我尝试加载此 ViewDidAppear 时...没有错误。但单独来看，这段代码在以前的 VIEW 上可以很好地获取数据。只有当我试图找出他们的线索时，我才会出错。

Answer 1

如果您的上下文是在主线程中创建的，则不能在后台使用它，反之亦然