Imports System.Threading



Public Class Form4



    Private _TV As New TreeView With {.Dock = DockStyle.Fill}

    Private _LB As New ListBox With {.Dock = DockStyle.Fill}

    Private _cts As CancellationTokenSource



    Private Sub Form4_Shown(sender As Object, e As EventArgs) Handles Me.Shown

        Dim sp As New SplitContainer With {.Dock = DockStyle.Fill}

        Dim root As New TreeNode("Task Cancel")

        Dim tn1 As New TreeNode("1")

        Dim tn2 As New TreeNode("2")

        Dim tn3 As New TreeNode("ListBox Clear")

        root.Nodes.AddRange({tn1, tn2, tn3})

        _TV.Nodes.Add(root)

        sp.Panel1.Controls.Add(_TV)

        sp.Panel2.Controls.Add(_LB)

        Controls.Add(sp)

        root.Expand()

        _TV.SelectedNode = root

        AddHandler _TV.AfterSelect, AddressOf TreeView_AfterSelect

        KeyPreview = True

        AddHandler Me.KeyDown, Sub(o, k)

                                   If k.KeyCode = Keys.Escape Then

                                       _cts?.Cancel()

                                   End If

                               End Sub

    End Sub



    Private Async Sub TreeView_AfterSelect(sender As Object, e As TreeViewEventArgs)



        If _cts Is Nothing Then

            _cts = New CancellationTokenSource

        Else

            _cts.Cancel()

            Task.Delay(20).Wait()

            _cts = New CancellationTokenSource

        End If





        Select Case e.Node.Text

            Case "1"

                Await Task.Run(Sub()



                                   For Each item In Enumerable.Range(1, 10000)

                                       Task.Delay(1).Wait()



                                       If _cts.Token.IsCancellationRequested Then

                                           Invoke(Sub() _LB.Items.Add("1 キャンセル　★★★★★★★★★★★★★★★★★★★★★★★★"))

                                           Return

                                       End If



                                       SetText($"Node1({item})")

                                   Next



                               End Sub, _cts.Token)



            Case "2"



                Await Task.Run(Sub()

                                   'Try 

                                   For Each item In Enumerable.Range(1, 10000)

                                       Task.Delay(1).Wait()



                                       If _cts.Token.IsCancellationRequested Then

                                           Invoke(Sub() _LB.Items.Add("2 キャンセル　★★★★★★★★★★★★★★★★★★★★★★★★"))

                                           Return

                                       End If

                                       SetText($"Node2({item})")

                                   Next



                               End Sub, _cts.Token)



            Case "ListBox Clear"

                _LB.Items.Clear()

        End Select



    End Sub



    Private Sub SetText(s As String)

        If InvokeRequired Then

            Invoke(Sub() SetText(s))

        Else

            _LB.Items.Add(s)

        End If

    End Sub

End Class