无法在Swift 4.2中撤消、重做和再次撤消

在swift 4.2中，我无法在初始撤销后重做然后撤销。UndoManager.registerUndo中的选择器。。。在重做和后续撤消期间从不调用

我在项目和操场上都尝试过，变化无穷

import Cocoa

class UndoResponder: NSObject {
    @objc func printSender(_ sender: Any) {
        print("printSender: ", sender)
    }
}

var undoResponder = UndoResponder()
var undoManager = UndoManager()
undoManager.registerUndo(withTarget: undoResponder, selector:
    #selector(UndoResponder.printSender(_:)), object: "Hi!")

print("about to undo")
undoManager.undo()
print("about to redo")
undoManager.redo()
print("about to undo")
undoManager.undo()

// output:
// about to undo
// printSender:  Hi!
// about to redo
// about to undo

预期产出：

// about to undo 
// printSender:  Hi! 
// about to redo 
// printSender:  Hi! 
// about to undo 
// printSender:  Hi!

---

正如问题评论中指出的，我没有注册重做。因此，我将其替换为以下内容：

import Cocoa

class Undoable {
    var undoManager = UndoManager()
    var object: Any = "None"

    @objc func setObject(_ newObject: Any) {

        let oldObject = object
        object = newObject

        undoManager.registerUndo(withTarget: self, selector:
            #selector(Undoable.setObject(_:)), object: oldObject)
    }

    func undo() {
        undoManager.undo()
        print("after undo: ", object)
    }

    func redo() {
        undoManager.redo()
        print("after redo: ", object)
    }
}

let undoable = Undoable()

print("Initial: ", undoable.object)
undoable.setObject(1)
print("After set: ", undoable.object)
undoable.undo()
undoable.redo()
undoable.undo()

输出：

Initial:  (None)
After set:  1
after undo:  (None)
after redo:  1
after undo:  (None)

---

撤消不注册重做。看@Willeke，噢！