如何在 Swift 中为 NSUndoManager 获取正确的回调值？答案

【问题标题】：How to get the correct callback value for NSUndoManager in Swift?如何在 Swift 中为 NSUndoManager 获取正确的回调值？
【发布时间】：2014-06-22 06:41:35
【问题描述】：

我有一个NSDocument 子类，连接到NSArrayController。作为参考，我正在尝试翻译 Cocoa Programming for Mac OS X Fourth Edition 第 9 章中的示例。

从我之前问过的this question看来，我需要对NSUndoManager使用基于对象的撤消。为了将两个值传递给被调用的方法，我将它们打包到带有两个实例变量的NSObject 子类中。

当通过单击我的应用程序中的按钮调用从 employees 数组中插入和删除的 KVO 方法时，它们按预期工作。

但是，当在撤消操作期间调用removeObjectFromEmployeesAtIndex 时，传入的index 非常超出范围（对于第一行，它似乎总是55，然后索引增加到接下来的几行有数千个）。

如何获得正确的索引来执行撤消操作？

class Document: NSDocument {

  var employee_list: Array<Person> = []

  var employees: Array<Person> {

  get {
    return self.employee_list
  }

  set {
    if newValue == self.employee_list {
      return
    }

    self.employee_list = newValue
  }

  }

  func insertObject(person: Person, inEmployeesAtIndex index: Int) {
    self.undoManager.registerUndoWithTarget(self, selector: Selector("removeObjectFromEmployeesAtIndex:"), object: index)

    if (!self.undoManager.undoing) {
      self.undoManager.setActionName("Add Person")
    }

    employees.insert(person, atIndex: index)
  }

  func removeObjectFromEmployeesAtIndex(index: Int) {
    let person = self.employees[index]
    let pair   = PersonIndexPair(person: person, index: index)

    self.undoManager.registerUndoWithTarget(self, selector: Selector("insertPersonIndexPair:"), object: pair)

    if (!self.undoManager.undoing) {
      self.undoManager.setActionName("Remove Person")
    }

    employees.removeAtIndex(index)
  }
  func insertPersonIndexPair(pair: PersonIndexPair) {
    insertObject(pair.person, inEmployeesAtIndex: pair.index)
  }

}

编辑：我通过传递一个字符串来解决这个问题，但这似乎很迟钝：

self.undoManager.registerUndoWithTarget(self, selector: Selector("removeObjectFromEmployeesAtStringIndex:"), object: String(index))

//...

func removeObjectFromEmployeesAtStringIndex(index: String) {
  if let i = index.toInt() {
    removeObjectFromEmployeesAtIndex(i)
  }
}

【问题讨论】：

标签： macos cocoa swift

【解决方案1】：

使用 NSNumber 代替 Int。

self.undoManager.registerUndoWithTarget(self, selector:Selector("removeObjectFromEmployeesAtStringIndex:"), object: NSNumber(integer: index))

//...

func removeObjectFromEmployeesAtStringIndex(index: NSNumber) {
    removeObjectFromEmployeesAtIndex(index.integerValue)
}

【讨论】：

【解决方案2】：

我现在正在阅读 Mac OS X 的 Cocoa Programming。我将示例 Object-C 代码翻译如下，只需将其附加到类 Document：

func insertObject(p: Person, inEmployeesAtIndex index: Int) {
    //NSLog("adding %@ to %@", p, employees)

    let undo = self.undoManager
    undo!.prepareWithInvocationTarget(self).removeObjectFromEmployeesAtIndex(index)
    if !undo!.undoing {
        undo!.setActionName("Add Person")
    }

    employees.insertObject(p, atIndex: index)
}

func removeObjectFromEmployeesAtIndex(index: Int) {
    let p = employees.objectAtIndex(index) as! Person

    //NSLog("Removing %@ from %@", p, index)

    let undo = self.undoManager
    undo!.prepareWithInvocationTarget(self).insertObject(p, inEmployeesAtIndex: index)

    if !undo!.undoing {
        undo!.setActionName("Remove Person")
    }

    employees.removeObjectAtIndex(index)
}

【讨论】：

【解决方案3】：

我认为完全替换老式的 Objective-C NSUndoManager 方法是最干净的：

private class SwiftUndoPerformer: NSObject {
    let closure: Void -> Void

    init(closure: Void -> Void) {
        self.closure = closure
    }

    @objc func performWithSelf(retainedSelf: SwiftUndoPerformer) {
        closure()
    }
}

extension NSUndoManager {
    func registerUndo(closure: Void -> Void) {
        let performer = SwiftUndoPerformer(closure: closure)
        registerUndoWithTarget(performer, selector: Selector("performWithSelf:"), object: performer)
        //(Passes unnecessary object to get undo manager to retain SwiftUndoPerformer)
    }
}

然后你可以快速注册任何闭包，而不必担心包装东西以绕过过时的接口：

undoManager.registerUndo {
    self.insertObject(person, inEmployeesAtIndex: index)
}

【讨论】：