重做在 swift 中无法在 UndoManager 中工作答案

【问题标题】：Redo not working in UndoManager in swift重做在 swift 中无法在 UndoManager 中工作
【发布时间】：2019-01-10 03:57:58
【问题描述】：

我正在我的代码中实现撤消/重做功能，但由于某种原因，我的重做功能无法正常工作，这是我的文本视图代码：

  func textViewDidBeginEditing(_ textView: UITextView) {
    if descBox.textColor == .lightGray {
        DescriptionCell.descPlaceholder = descBox.text
            let descText = descBox.text
            undoManager?.registerUndo(withTarget: self, handler: {
            (targetSelf) in
            targetSelf.descBox.text = descText
            targetSelf.descBox.textColor = .lightGray
        })
        descBox.text = nil
        descBox.textColor = .black
    }
}

func textViewDidEndEditing(_ textView: UITextView) {
    if descBox.text.isEmpty {
        descBox.text = DescriptionCell.descPlaceholder
        descBox.textColor = .lightGray
    }
        let descText = descBox.text
        undoManager?.registerUndo(withTarget: self, handler: {
            (targetSelf) in
            targetSelf.descBox.text = descText
        })
        }

然后我将它用于我的 ViewController 工具栏：

@objc func Undo() {
 undoManager?.undo()
}

@objc func Redo() {
 undoManager?.redo()
}

然后在viewDidLoad中：

let undoKeyboard = UIBarButtonItem(image: UIImage(named: "Image-2"), style: .plain, target: self, action: #selector(Undo))
    undoKeyboard.tintColor = .lightGray
let redoKeyboard = UIBarButtonItem(image: UIImage(named: "Image-1"), style: .plain, target: self, action: #selector(Redo))
    redoKeyboard.tintColor = .green

【问题讨论】：

标签： ios swift xcode undo-redo nsundomanager

【解决方案1】：

这里的问题：

func textViewDidEndEditing(_ textView: UITextView) {
    if descBox.text.isEmpty {
        descBox.text = DescriptionCell.descPlaceholder
        descBox.textColor = .lightGray
    }

    let descText = descBox.text // <== Incorrect; Text has been set
    undoManager?.registerUndo(withTarget: self, handler: { (targetSelf) in
        // Here it means to reset the text (which already set in textDidEnd), thus meaningless (unless you made changes somewhere else and want to reset to the set text, which I assume is not what you want to achieve here)
        targetSelf.descBox.text = descText
    })
}

您在此处写的是使用一组文本注册撤消管理器（textViewDidEndEditing 表示该字段已更改，因此 descBox.text 已更新）。

我建议您将其更改为textViewDidBeginEditing(_:) 并在那里注册撤消管理器。示例：

func textViewDidBeginEditing(_ textView: UITextView) {

    let descText = descBox.text
    undoManager?.registerUndo(withTarget: self, handler: { (targetSelf) in
        targetSelf.descBox.text = descText
        targetSelf.descBox.resignFirstResponder()
    })
}

在那里，当您按下撤消时，它将设置先前的文本（在任何更改之前）并辞去第一响应者（a.k.a endEditing()）

【讨论】：