iOS 键盘：textDocumentProxy.documentContextBeforeInput.isEmpty 意外返回 Nil（不应该返回）

Question

我正在开发自定义 iOS 键盘 – 大部分都已就绪，但我在使用删除键时遇到问题，更具体地说，在删除整个单词时遇到问题。

问题是 self.textDocumentProxy.documentContextBeforeInput?.isEmpty returns Nil 即使文本字段中还有剩余字符。

背景介绍：如果您不熟悉，它在标准 iOS 键盘上的工作方式是在按住退格键的同时，系统一次删除一个字符（前 10 个字符）。 10 个字符后，开始删除整个单词。

在我的代码中，我删除了 10 个单个字符，然后成功删除了几个完整的单词，然后突然 self.textDocumentProxy.documentContextBeforeInput?.isEmpty returns Nil，即使有是文本字段中剩余的字符。

我查看了所有文档和网络，没有看到其他人有同样的问题，所以我确定我遗漏了一些明显的东西，但我感到困惑。

以下是我的 class 定义的相关部分：

class KeyboardViewController: UIInputViewController { 

//I've removed a bunch of variables that aren't relevant to this question.

    var myInputView : UIInputView {
    return inputView!
}
private var proxy: UITextDocumentProxy {
    return textDocumentProxy
}
override func canBecomeFirstResponder() -> Bool {
    return true
}

override func viewDidLoad() {
    super.viewDidLoad()
    //proxy let proxy = self.textDocumentProxy


    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillAppear"), name: UIKeyboardWillShowNotification, object: nil)
    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide"), name: UIKeyboardWillHideNotification, object: nil)


    self.myInputView.translatesAutoresizingMaskIntoConstraints = true

    // Perform custom UI setup here
    view.backgroundColor = UIColor(red: 209 / 255, green: 213 / 255, blue: 219 / 255, alpha: 1)

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "touchUpInsideLetter:", name: "KeyboardKeyPressedNotification", object: nil)

    showQWERTYKeyboard()
}

我为退格按钮设置了侦听器和操作，因为我还在按钮上配置了一堆其他属性。我在 Switch 中这样做——相关部分在这里：

case "<<":
            isUIButton = true
            normalButton.setTitle(buttonString, forState: UIControlState.Normal)
            normalButton.addTarget(self, action: "turnBackspaceOff", forControlEvents: UIControlEvents.TouchUpInside)
            normalButton.addTarget(self, action: "turnBackspaceOff", forControlEvents: UIControlEvents.TouchUpOutside)
            normalButton.addTarget(self, action: "touchDownBackspace", forControlEvents: UIControlEvents.TouchDown)
            let handleBackspaceRecognizer : UILongPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: "handleBackspaceLongPress:")
            normalButton.addGestureRecognizer(handleBackspaceRecognizer)

            buttonWidth = standardButtonWidth * 1.33
            nextX = nextX + 7

感谢您提供任何想法。

**** 修改原始 post 以帮助更清楚地说明问题 **** 以下是旨在创建退格行为的 4 个函数。它们似乎至少对前两个完整单词工作正常，但随后正确建议的可选检查开始评估为 nil 并停止删除。

    //Gets called on "Delete Button TouchUpInside" and "Delete Button TouchUpOutside"
func turnBackspaceOff() {

    self.backspaceIsPressed = false
    keyRepeatTimer.invalidate()

}

//Handles a single tap backspace
func touchDownBackspace() {

    (textDocumentProxy as UIKeyInput).deleteBackward()

}

//Handles a long press backspace
func handleBackspaceLongPress(selector : UILongPressGestureRecognizer) {

    if selector.state == UIGestureRecognizerState.Began {
        self.backspaceIsPressed = true
        self.keyRepeatTimer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: "backspaceRepeatHandlerFinal", userInfo: nil, repeats: true)
        print("handleBackspaceLongPress.Began")
    }
    else if selector.state == UIGestureRecognizerState.Ended {
        self.backspaceIsPressed = false
        keyRepeatTimer.invalidate()
        numberOfKeyPresses = 0
        print("handleBackspaceLongPress.Ended")
    }
    else {
        self.backspaceIsPressed = false
        keyRepeatTimer.invalidate()
        numberOfKeyPresses = 0
        print("handleBackspaceLongPress. Else")
    }

}

func backspaceRepeatHandlerFinal() {

        if let documentContext = proxy.documentContextBeforeInput as String? {
            print(documentContext)
        }

        print("backspaceRepeatHandlerFinal is called")
        if self.backspaceIsPressed {
            print("backspace is pressed")
            self.numberOfKeyPresses = self.numberOfKeyPresses + 1

            if self.numberOfKeyPresses < 10 {

                    proxy.deleteBackward()

            }
            else {

                if let documentContext = proxy.documentContextBeforeInput as NSString? {
                        let tokens : [String] = documentContext.componentsSeparatedByString(" ")
                        var i : Int = Int()
                    for i = 0; i < String(tokens.last!).characters.count + 1; i++ {
                            (self.textDocumentProxy as UIKeyInput).deleteBackward()
                        }

                }
                else {
                    print("proxy.documentContextBeforeInput was nil")
                    self.keyRepeatTimer.invalidate()
                    self.numberOfKeyPresses = 0
                }
            }
        }
        else {
            print("In the outer else")
            self.keyRepeatTimer.invalidate()
            self.numberOfKeyPresses = 0
        }
}

最后，我不完全明白为什么，但是XCode在我创建键盘扩展时自动在下面插入了这两个函数。我对它们进行了一些修改，试图让它发挥作用。

    override func textWillChange(textInput: UITextInput?) {
    // The app is about to change the document's contents. Perform any preparation here.
    super.textWillChange(textInput)
}

override func textDidChange(textInput: UITextInput?) {
    // The app has just changed the document's contents, the document context has been updated.

    var textColor: UIColor
    //let proxy = self.textDocumentProxy
    if proxy.keyboardAppearance == UIKeyboardAppearance.Dark {
        textColor = UIColor.whiteColor()
    } else {
        textColor = UIColor.blackColor()
    }
    super.textDidChange(textInput)
}

Answer 1

让我们描述一下下面这行代码的作用：

if !((self.textDocumentProxy.documentContextBeforeInput?.isEmpty) == nil) {

首先，它需要一个标记为 optional 的对象（由 ? 字母）：

let documentContext = self.textDocumentProxy.documentContextBeforeInput

然后，它尝试读取名为 isEmpty:

的属性

let isEmpty = documentContext?.isEmpty

然后它计算条件：

if !(isEmpty == nil) {

有两个错误。第一个是您将 Bool 值与 nil 进行比较。另一个是您不确定 documentContext 不是 nil.

所以，让我们以更合适的方式编写您的代码：

if let documentContext = self.textDocumentProxy.documentContextBeforeInput { // Make sure that it isn't nil
    if documentContext.isEmpty == false { // I guess you need false?
        // Do what you want with non-empty document context
    }
}

iOS 键盘：textDocumentProxy.documentContextBeforeInput.isEmpty 意外返回 Nil（不应该返回）

iOS Keyboard: textDocumentProxy.documentContextBeforeInput.isEmpty Unexpectedly Returning Nil (when it shouldn't)

ios

swift

custom-keyboard