swift 数组不包含实例变量

Question

import UIKit

class KeyboardViewController: UIInputViewController, UIImagePickerControllerDelegate,     UINavigationControllerDelegate {

@IBOutlet var nextKeyboardButton: UIBarButtonItem
var statusLabel: UILabel  = UILabel()
var bottomBar : UIToolbar = UIToolbar()


var globeIcon : UIImage = UIImage(named: "globe-hover.png")
@IBOutlet var captureButton : UIBarButtonItem
@IBOutlet var libraryButton : UIBarButtonItem


override func viewDidLoad() {

    super.viewDidLoad()

    self.statusLabel.text="viewDidLoad() called"
    // Perform custom UI setup here
    self.nextKeyboardButton = UIBarButtonItem(image: self.globeIcon, style: .Plain , target: self, action: "advanceToNextInputMode")
    self.captureButton = UIBarButtonItem(title: "Take Photo", style: .Plain, target: self, action: "captureClicked")
    self.libraryButton = UIBarButtonItem(title: "Library", style: .Plain, target: self, action: "libraryClicked")

    self.statusLabel.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.statusLabel.sizeToFit()



   var barItems : [UIBarButtonItem] = [self.nextKeyboardButton, self.captureButton, self.libraryButton]

    self.bottomBar.items = barItems
    self.view.addSubview(self.bottomBar)
    self.view.addSubview(self.statusLabel)



    var statusLabelLeftSideConstraint = NSLayoutConstraint(item: self.statusLabel, attribute: .Right, relatedBy: .Equal, toItem: self.view, attribute: .Right, multiplier: 1.0, constant: 0.0)
    var statusLabelBottomConstraint = NSLayoutConstraint(item: self.statusLabel, attribute: .Top, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1.0, constant: 0.0)
    self.view.addConstraints([statusLabelLeftSideConstraint, statusLabelBottomConstraint])





}

每次运行此程序时，我都会收到运行时错误：“致命错误：在展开可选值时意外发现 nil”，指的是位 var barItems : [UIBarButtonItem] = [self.nextKeyboardButton, self.captureButton, self.libraryButton]，并且调试器指出 barItems 是一个空数组 (nil)。

这里发生了什么？为什么数组 barItems 不包含我的实例 UIBarButtonItem 变量？似乎 UIBarButtonItem 类型变量（captureButton、libraryButton 和 nextKeyboardButton）本身是 nil，但为什么呢？提前致谢！

Answer 1

由于目标 C 指针不具有 swift 提供的相同类型安全性这一事实，许多来自目标 C 的对象都是隐式展开的可选项。

您在这一行收到错误，因为类型 [UIBarButtonItem] 不允许数组中包含 nil 值，并且您放入数组中的某些值是 nil。 p>

var barItems : [UIBarButtonItem] = [self.nextKeyboardButton, self.captureButton, self.libraryButton]

为了使调试更简单，我要做的第一件事是向这些值的原始实例添加类型（您不希望是nil）：

self.nextKeyboardButton : UIBarButtonItem = UIBarButtonItem(image: self.globeIcon, style: .Plain , target: self, action: "advanceToNextInputMode")
self.captureButton : UIBarButtonItem = UIBarButtonItem(title: "Take Photo", style: .Plain, target: self, action: "captureClicked")
self.libraryButton : UIBarButtonItem = UIBarButtonItem(title: "Library", style: .Plain, target: self, action: "libraryClicked")

objective-c 中的一些初始化器返回 nil 表示初始化失败，也许这里就是这种情况？如果是，则添加类型注释后会出现不同的错误。你能发布那个错误吗？