SwiftUI UndoManager — 它是如何工作的，它是如何工作的？

编程问答 2022-12-13

问题描述

我正在尝试了解 UndoManager 的工作原理。我做了一个小应用程序来撤消/重做某事。 我有几个问题，我在文档中找不到答案：

  1. 我知道可以通过以下方式在视图中访问 UndoManager

    @Environment(\.undoManager) var undoManager

太棒了。但在这种情况下，它只在视图中可用，如果我想在结构中更深的地方使用它，我必须通过模型将它传递给对象......是一种在其他对象中访问相同 UndoManager 的方法吗？模型，数据...我可以更方便，特别是如果有很多撤消分组。如果我在 Document（或其他地方）中创建 UndoManager，它在主菜单 Edit -> Undo,Redo 中不可见

  1. 在应用 repository on GitHub 中，我实现了撤消/重做。对我来说 (haha) 看起来不错，甚至可以工作，但不适用于第一次行动。第一个操作撤消会导致 Thread 1: signal SIGABRT 错误。三个动作后，我可以撤消最后两个动作……砰。出了点问题

     import Foundation
 import SwiftUI

 struct CustomView: View {
     @Observedobject var model: Pointsviewmodel

     @Environment(\.undoManager) var undoManager

     @GestureState var isDragging: Bool = false
     @State var dragOffsetDelta = CGPoint.zero

     var formatter: NumberFormatter {
         let formatter = NumberFormatter()
         formatter.allowsFloats = true
         formatter.minimumFractionDigits = 2
         formatter.maximumFractionDigits = 5
         return formatter
     }

     var body: some View {
         HStack {
             vstack(alignment: .leading,spacing: 10) {
                 ForEach(model.insideDoc.points.indices,id:\.self) { index in
                     HStack {
                         TextField("X",value: $model.insideDoc.points[index].x,formatter: formatter)
                             .frame(width: 80,alignment: .topLeading)
                         TextField("Y",value: $model.insideDoc.points[index].y,alignment: .topLeading)
                         Spacer()
                     }

                 }
                 Spacer()
             }
         ZStack {
             ForEach(model.insideDoc.points.indices,id:\.self) { index in
                 Circle()
                     .foregroundColor(index == model.selectionIndex ? .red : .blue)
                     .frame(width: 20,height: 20,alignment: .center)
                     .position(model.insideDoc.points[index])

                     //MARK: - drag point
                     .gesture(DragGesture(minimumdistance: 0,coordinateSpace: .local)
                                 .onChanged { drag in
                                     if !isDragging {
                                         dragOffsetDelta = drag.location - model.insideDoc.points[index]
                                         model.selectionIndex = index
                                         let Now = model.insideDoc.points[index]
                                         undoManager?.registerUndo(withTarget: model,handler: { model in
                                             model.insideDoc.points[index] = Now
                                             model.objectwillChange.send()
                                         })
                                         undoManager?.setActionName("undo Drag")
                                     }
                                     model.insideDoc.points[index] = drag.location - dragOffsetDelta
                                 }
                                 .updating($isDragging,body: { drag,state,trans in
                                     state = true
                                     model.objectwillChange.send()
                                 })
                                 .onEnded({drag in model.selectionIndex = index
                                     model.insideDoc.points[index] = drag.location - dragOffsetDelta
                                     model.objectwillChange.send()
                                 })
                     )

             }
         }.background(Color.orange.opacity(0.5))

         //MARK: - new point
         .gesture(DragGesture(minimumdistance: 0,coordinateSpace: .local)
                     .onEnded{ loc in
                         let prevIoUsIndex = model.selectionIndex
                         undoManager?.registerUndo(withTarget: model,handler: {model in
                             model.insideDoc.points.removeLast()
                             model.selectionIndex = prevIoUsIndex
                             model.objectwillChange.send()
                         })
                         model.insideDoc.points.append(loc.location)
                         model.selectionIndex = model.insideDoc.points.count - 1
                         model.objectwillChange.send()
                     }

         )

         //MARK: - delete point
         .onReceive(deleteSelectedobject,perform: { _ in
             if let deleteIndex = model.selectionIndex {
                 let deleted = model.insideDoc.points[deleteIndex]
                 undoManager?.registerUndo(withTarget: model,handler: {model in
                     model.insideDoc.points.insert(deleted,at: deleteIndex)
                     model.objectwillChange.send()
                 })
                 undoManager?.setActionName("remove Point")
                 model.insideDoc.points.remove(at: deleteIndex)
                 model.objectwillChange.send()
                 model.selectionIndex = nil
             }
         })

     }
     }
 }

解决方法

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