使用NSUndoManager从异步撤消注册重做操作 [英] Registering a redo operation from an async undo with NSUndoManager

问题描述

使用UndoManager.registerUndo(withTarget:selector:object :)我可以注册一个撤消操作，并且在提供的选择器中调用此相同方法再次导致重做操作的注册.除非在选择器中我调用一个异步函数，然后需要注册重做操作，如下所示，否则此方法工作正常:

With UndoManager.registerUndo(withTarget:selector:object:) I can register an undo operation, and in the provided selector calling this same method again causes the registration of a redo operation. This works fine unless in the selector I'm calling an async function which then needs to register the redo operation, like this:

func job() {  
     doSomething()  
     registerUndo(self, undo)  
}  

func undo() {  
     async {  
          doSomethingElse()  
          registerUndo(self, job)  
     }  
}  

在这种情况下，两个对registerUndo()的调用实际上都注册了一个撤消操作，而不是我所期望的撤消然后是重做.有解决这个问题的方法吗?

In this case, both calls to registerUndo() actually register an undo operation, and not an undo and then a redo as I would expect. Is there a solution to this problem?

推荐答案

我发现具有一致的do/undo/redo机制的更好解决方案是使用Action对象

The better solution I found to have a coherent do/undo/redo mechanism is to use an Action object

class Action {
    var someContextInfo ( like added/removed elements and indexes )
    var actionType ( like add/remove )

    func execute()

    // Returns the symmetric action ( for example `add` will be a `remove` )
    var symmetric: Action 
}

func doAction(action: Action) {  
     action.execute()  
     manager.registerUndo(withTarget: self) { target in
         target.doAction(action.symetric)
     }
}  

使用此解决方案可以执行/撤消/重做异步操作，因为您可以保留上下文并跟踪操作(完成，失败，进行中.).

Using this solution makes possible to do/undo/redo asynchronous operations, since you keep the context and keep track of actions ( finished, failed, in progress.. ).

但是正如评论中所说，这是一种罕见的情况.

But as said in the comments, it is an uncommon situation.

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