swift - 尝试执行 segue 导致 "terminating with uncaught exception of type NSException"

Question

我有一个 UITableView VC，其中的单元格链接到 prepare for segue 函数，这很有效。它移动到正确的 VC。 我在链接到调用 performForSegue 的方法的导航项上添加了 rightBarButtonItem，并为其提供了正确的标识符。在我单击右侧按钮之前，一切都运行良好。当我这样做时，我得到:“首先抛出调用堆栈。以 NSException 类型的未捕获异常终止”有人可以帮助我并指出正确的方向吗？下面的代码和打印 list 。谢谢。

class AssignNumberOfRoomsForFloorsVC: UITableViewController {

//MARK: - Properties

private var managedObjectContext: NSManagedObjectContext!

private var storedFloors = [Floors]()


//MARK: - Actions

override func viewDidLoad() {
    super.viewDidLoad()
    managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    loadFloorData()
    self.tableView.reloadData()
    self.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.done, target: self, action: Selector(("navigateToNextViewController")))

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

private func loadFloorData() {
    let request: NSFetchRequest<Floors> = Floors.fetchRequest()
    request.returnsObjectsAsFaults = false
    do {
        storedFloors = try managedObjectContext.fetch(request)
    }
    catch {
        print("could not load data from core \(error.localizedDescription)")
    }
}

private func navigateToNextViewController(){
    self.performSegue(withIdentifier: "room and alarm type", sender: self)
}



// MARK: - Table view data source

override func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return storedFloors.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "floor cell", for: indexPath) as! FloorCell
    let floorItem = storedFloors[indexPath.row]
    cell.floorNumberTxt.text = String(floorItem.floorNumber)
    return cell
}

// MARK: - Navigation

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    var selectedRow = self.tableView.indexPathForSelectedRow
    let floorItem = storedFloors[(selectedRow?.row)!]
    let destinationController = segue.destination
    if let assignRoomsVC = destinationController as? DeclareRoomsVC {
        if let identifier = segue.identifier {
            switch identifier {
            case "assign number of rooms":
                let _ = assignRoomsVC.view
                assignRoomsVC.floorNumberTxt.text = String(floorItem.floorNumber)
                assignRoomsVC.selectedFloor = floorItem.floorNumber
            default: break
            }
        }
    }
}

这是控制台中的消息:

2017-03-26 21:50:28.041 PDCiPad[10433:292572] -[PDCiPad.AssignNumberOfRoomsForFloorsVC navigateToNextViewController]: unrecognized selector sent to instance 0x7ff5b7c326c0

2017-03-26 21:50:28.219 PDCiPad[10433:292572] * 由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因:“-[PDCiPad.AssignNumberOfRoomsForFloorsVC navigateToNextViewController]:无法识别的选择器已发送到实例 0x7ff5b07c326c ' * 首先抛出调用栈: ( 0 CoreFoundation 0x000000010db79d4b 异常预处理 + 171 1 libobjc.A.dylib 0x000000010d1ba21e objc_exception_throw + 48 2 CoreFoundation 0x000000010dbe9f04 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132 3 CoreFoundation 0x000000010daff005 ___forwarding_ + 1013 4 CoreFoundation 0x000000010dafeb88 _CF_forwarding_prep_0 + 120 5 UIKit 0x000000010e6b28bc -[UIApplication sendAction:to:from:forEvent:] + 83 6 UIKit 0x000000010eaf44a1 -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 149 7 UIKit 0x000000010e6b28bc -[UIApplication sendAction:to:from:forEvent:] + 83 8 UIKit 0x000000010e838c38 -[UIControl sendAction:to:forEvent:] + 67 9 UIKit 0x000000010e838f51 -[UIControl _sendActionsForEvents:withEvent:] + 444 10 UIKit 0x000000010e8390db -[UIControl _sendActionsForEvents:withEvent:] + 838 11 UIKit 0x000000010e837e4d -[UIControl touchesEnded:withEvent:] + 668 12 UIKit 0x000000010e720545 -[UIWindow _sendTouchesForEvent:] + 2747 13 UIKit 0x000000010e721c33 -[UIWindow 发送事件:] + 4011 14 UIKit 0x000000010e6ce9ab -[UIApplication sendEvent:] + 371 15 UIKit 0x000000010eebb72d <强>dispatchPreprocessedEventFromEventQueue + 3248 16 UIKit 0x000000010eeb4463 __handleEventQueue + 4879 17 CoreFoundation 0x000000010db1e761 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION + 17 18 核心基础 0x000000010db0398c __CFRunLoopDoSources0 + 556 19 核心基础 0x000000010db02e76 __CFRunLoopRun + 918 20 核心基础 0x000000010db02884 CFRunLoopRunSpecific + 420 21 图形服务 0x0000000113908a6f GSEventRunModal + 161 22 UIKit 0x000000010e6b0c68 UIApplicationMain + 159 23 PDCiPad 0x000000010cad8c1f 主 + 111 24 libdyld.dylib 0x0000000111a3268d 开始 + 1 ) libc++abi.dylib:以 NSException 类型的未捕获异常终止

Answer 1

当您点击 UIBarButtonItem 时，selectedRow 为 nil 因为您使用了 indexPathForSelectedRow 而您没有选择任意行。

override func prepare(for segue: UIStoryboardSegue, sender: Any?) 如果您点击您的 UIBarButtonItem 或 tableView 单元格，将被调用。

所以当您单击 tableView 单元格时它会起作用，因为 self.tableView.indexPathForSelectedRow 将返回所选单元格的索引。但是将为您的 UIBarButtonItem 返回 nil。

最后，如果您在 nil 值上使用 !，您会崩溃。