ios - 当用户编辑待处理的 Swift 3 时，防止 View 在 splitview 中消失

Question

我有一个通用的主从应用程序，我可以在其中展示主信息以及 iPad 上两个方向并排的详细 View 。当一个用户在 iPhone 上的详细 View 中进行更改，我可以轻松检测到更改并显示警报，询问他们是否要保存更改或丢失它们(CoreData)。在 iPad 上，不禁止简单地点击在主列表中，从而丢失编辑。

我在 DetailViewController viewWillDisappear 中放置了一个函数(对于 iPad)会引发警报，但编译器告诉我确实如此与在非连接 View 上呈现 View 不同。

控制台消息:在分离 View 上呈现 View Controller 不鼓励 Controller <>.

有没有更合适的方法来处理这个问题？ Swift 3、iOS 10、Xcode 8.2.1

var hasChanged //set to true whenever edits are made

override func viewWillDisappear(_ animated: Bool) {

    if UIDevice.current.model == "iPad" {
        if hasChanged {
            print("hasChanged (should be true) is: \(hasChanged)")
            cancelUnsavedEdits()
        }//if hasChanged
    }//if ipad

}//viewWillDisappear

func cancelUnsavedEdits() {

    if hasChanged {

        let ac = UIAlertController(title: nil, message: nil, preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "Delete Edits", style: .default, handler: { (action : UIAlertAction!) -> Void in

            self.codeDismissTheKeyboard()
            self.performSegue(withIdentifier: "unwindToMasterViewController", sender: self)

            let editRecordButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.edit, target: self, action: #selector(DetailViewController.editThisRecord))
            self.navigationItem.rightBarButtonItem = editRecordButton

            self.navigationItem.leftBarButtonItem = nil
            self.navigationItem.hidesBackButton = false

            //need to remove the edits - refresh the original page
            self.configureView()

        }))//addAction block

        ac.addAction(UIAlertAction(title: "Save Edits", style: .default, handler: { (action : UIAlertAction!) -> Void in
            self.codeDismissTheKeyboard()
            self.saveTheEditedRecord()
            self.performSegue(withIdentifier: "unwindToMasterViewController", sender: self)
        }))//addAction block

        //ac.addAction(UIAlertAction(title: "Cancel", style: .default, handler: nil))

        //try this - for -ipad add code in handler to reopen the fields for editing if the cancel of the cancel is chosen
        ac.addAction(UIAlertAction(title: "Cancel", style: .default, handler: { (whatever) in
            self.makeEntryFieldsEnabledYES()
            let cancelItemButton = UIBarButtonItem(barButtonSystemItem: .cancel, target: self, action: #selector(DetailViewController.cancelUnsavedEdits))
            self.navigationItem.leftBarButtonItem = cancelItemButton
        }))
        //try above

        self.present(ac, animated: true, completion: nil)

    } else {
        self.codeDismissTheKeyboard()

        //for ipad
        self.navigationItem.rightBarButtonItem = nil

        self.performSegue(withIdentifier: "unwindToMasterViewController", sender: self)
    }//if hasChanged

    //for ipad
    navigationItem.leftBarButtonItem = nil

}//cancelUnsavedEdits

Answer 1

我认为问题是您尝试在 View Controller 上呈现一个新的 View Controller ，该 View Controller 将从 View 层次结构中删除。

也许一个肮脏的修复可以是替换:

self.present(ac, animated: true, completion: nil)

至:

self.view.window.rootViewController?.present(ac, animated: true, completion: nil);