Swift-通过代码链接UIViewController

Question

我试图将一个编辑按钮链接回我的UIViewController（AddfreshreleaseViewController）。 当您向右滑动单元格时，此代码在左侧显示编辑按钮，但是当我添加“ performSegue”以尝试返回UIViewController时，每次我向右滑动编辑按钮时，应用程序都会崩溃。 关于如何使它工作的任何建议？

@available(iOS 11.0, *)
override func tableView(_ tableView: UITableView,
               leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration?

{
    let modifyAction = UIContextualAction(style: .normal, title:  "Update", handler: { (ac:UIContextualAction, view:UIView, success:(Bool) -> Void) in
        print("Update action ...")
        success(true)

    })
    modifyAction.title = "Edit"
    modifyAction.backgroundColor = .blue

    performSegue(withIdentifier: "addFreshRelease", sender: self)

    return UISwipeActionsConfiguration(actions: [modifyAction])

}

这是我用于FreshReleaseTableViewController的代码：

import UIKit
import CoreData
import UserNotifications

class FreshReleaseTableViewController: UITableViewController{

    var freshreleases = [Release_Date]()

let dateFormatter = DateFormatter()

override func viewDidLoad() {
    super.viewDidLoad()



    //create a new button
    let button = UIButton.init(type: .custom)
    //set image for button
    button.setImage(UIImage(named: "Mic App Logo.png"), for: UIControlState.normal)

    dateFormatter.dateStyle = .full
    dateFormatter.timeStyle = .none


    //let button1 = UIButton()
    //button1.addTarget(self, action: #selector(editAction), for: .touchUpInside)

    //self.tableView.backgroundColor = UIColor.white

}

/* @objc func editAction() {
    let viewController = AddfreshreleaseViewController()
    navigationController?.present(viewController, animated: true, completion: nil)
}*/

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext

    let fetchRequest = Release_Date.fetchRequest() as NSFetchRequest<Release_Date>

    let sortDescriptor1 = NSSortDescriptor(key: "artist", ascending: true)
    let sortDescriptor2 = NSSortDescriptor(key: "album", ascending: true)
    fetchRequest.sortDescriptors = [sortDescriptor1, sortDescriptor2]
    do {
        freshreleases = try context.fetch(fetchRequest)
    } catch let error {
        print("Could not fetch because of error: \(error).")
    }
    tableView.reloadData()
}


// MARK: - Table view data source

override func numberOfSections(in tableView: UITableView) -> Int {
    // #warning Incomplete implementation, return the number of sections
    return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // #warning Incomplete implementation, return the number of rows
    return freshreleases.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {



    let cell = tableView.dequeueReusableCell(withIdentifier: "FreshReleaseCellIdentifier", for: indexPath)

    let freshrelease = freshreleases[indexPath.row]

        cell.textLabel?.numberOfLines = 0


    let artist = freshrelease.artist ?? ""
    let album = freshrelease.album ?? ""
    cell.textLabel?.text = artist + "'s \nnew album '" + album + "'\nreleases"

    if let date = freshrelease.release_date as Date? {
        cell.detailTextLabel?.text = dateFormatter.string(from: date)
    } else {
        cell.detailTextLabel?.text = ""
    }

    return cell
}


// Override to support conditional editing of the table view.
override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
    // Return false if you do not want the specified item to be editable.
    return true
}



// Override to support editing the table view.
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
    if freshreleases.count > indexPath.row {
        let freshrelease = freshreleases[indexPath.row]

        // Remove notification
        if let identifier = freshrelease.release_dateId {
            let center = UNUserNotificationCenter.current()
            center.removePendingNotificationRequests(withIdentifiers: [identifier])
        }


        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let context = appDelegate.persistentContainer.viewContext
        context.delete(freshrelease)
        freshreleases.remove(at: indexPath.row)
        do {
            try context.save()
        } catch let error {
            print("Could not save \(error)")
        }
        tableView.deleteRows(at: [indexPath], with: .fade)

    }
}



@available(iOS 11.0, *)
override func tableView(_ tableView: UITableView,
               leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration?

{
    let modifyAction = UIContextualAction(style: .normal, title:  "Update", handler: { (ac:UIContextualAction, view:UIView, success:(Bool) -> Void) in
        print("Update action ...")
        success(true)

    })
    modifyAction.title = "Edit"
    modifyAction.backgroundColor = .blue

    return UISwipeActionsConfiguration(actions: [modifyAction])

}

/*
// Override to support rearranging the table view.
override func tableView(_ tableView: UITableView, moveRowAt fromIndexPath: IndexPath, to: IndexPath) {

}
*/

override func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
    return true
}

}

这是AddfreshreleaseViewController的代码：

import UIKit
import CoreData
import UserNotifications

class AddfreshreleaseViewController: UIViewController {

@IBOutlet var artisttextfield: UITextField!
@IBOutlet var albumtextfield: UITextField!
@IBOutlet var releasedatePicker: UIDatePicker!


override func viewDidLoad() {
    super.viewDidLoad()

    releasedatePicker.minimumDate = Date()

    // Do any additional setup after loading the view, typically from a nib.
}
@IBAction func saveTapped( _ sender: UIBarButtonItem) {

    let artist = artisttextfield.text ?? ""
    let album = albumtextfield.text ?? ""
    let releasedate = releasedatePicker.date

    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext

    let newRelease = Release_Date(context: context)
    newRelease.artist = artist
    newRelease.album = album
    newRelease.release_date = releasedate as NSDate?
    newRelease.release_dateId = UUID().uuidString

    if let uniqueId = newRelease.release_dateId {
        print("The freshreleaseId is \(uniqueId)")
    }

    do {
        try context.save()
        let message = "\(artist)'s new album \(album) releases Today!"
        let content = UNMutableNotificationContent()
        content.body = message
        content.sound = UNNotificationSound.default()
        var dateComponents = Calendar.current.dateComponents([.month, .day],
            from: releasedate)
        dateComponents.hour = 09
        dateComponents.minute = 00
        let trigger = UNCalendarNotificationTrigger(dateMatching: dateComponents,
            repeats: true)
        if let identifier = newRelease.release_dateId {

            let request = UNNotificationRequest(identifier: identifier,
                content: content, trigger: trigger)
            let center = UNUserNotificationCenter.current()
            center.add(request, withCompletionHandler: nil)
        }
    } catch let error {
        print("Could not save because of \(error).")
    }

    dismiss(animated: true, completion: nil)

    print("Added a Release Date!")
    print("Artist: \(newRelease.artist)")
    print("Album: \(newRelease.album)")
    print("Release Date: \(newRelease.release_date)")
}

@IBAction func cancelTapped(_ sender: UIBarButtonItem) {
    dismiss(animated: true, completion: nil)
}



}

所以我要做的是，在FreshReleaseTableViewController中按下编辑按钮时，它将弹出AddfreshreleaseViewController。

但是，编辑按钮是用代码编写的，而不是实际上是条形按钮的项目。

更复杂的是，当用户转到AddfreshreleaseViewController时，他们会将信息输入三个字段（艺术家，专辑和发行日期），并将其保存在FreshReleaseTableViewController上。 因此，当FreshReleaseTableViewController中的编辑按钮将它们带回到AddfreshreleaseViewController时，我需要在三个字段中输入的用户信息（艺术家，专辑和发行日期），以便用户可以编辑字段（如果有的话）。初始输入有误。

Answer 1

信息太少，但我会尝试猜测您遇到的行为。

但是，为什么要在完成configureAction时执行perfomSegue？ 您应该使用以下命令弹出当前视图控制器：

https://developer.apple.com/documentation/uikit/uinavigationcontroller/1621886-popviewcontroller

例：

 _ = navigationController?.popViewController(animated: true)

Answer 2

我不确定您问题的确切性质，但是如果您（a）使用情节提要定义的segue将数据从ViewController1移至ViewController2 ，然后希望（b）在“展开”中将已编辑的数据移回第一个VC通常是使用左侧导航按钮完成的，下面的代码将完成此操作：

在您的第一个VC（ ViewController1 ）中，定义您想要从第二个VC（ ViewController2 ）获得的内容，然后在segue中发送self ：

var someData:String!

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "ShowViewController2" {
        if let vc = segue.destination as? ViewController2 {
            vc.firstVC = self
        }
    }
}

在第二个视图控制器中，定义第一个VC（ weak ），然后将数据传递回viewWillDisappear ，并且UIViewController属性为isMovingFromParentViewController 。

weak var firstVC:ViewController1!

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    if isMovingFromParentViewController {
        firstVC.someData = "Hello world!"
    }
}