Question

我有一些带有一些数据的数据网格，我正在通过for ...下一个项目循环在循环内部，我使用来自datagrid的参数调用Web服务由于速度很快，工作非常耗时，我想让用户可以选择多次调用他想要的服务。如何在循环内同时调用Web服务？

Answer 1

有很多方法可以达到你想要的效果，所以这里有一个使用Task类的例子。关键点是在后台线程内迭代底层数据源（只读）。完成后，返回UI线程并更新。

Private Sub BeginAsyncOp(list As IList)

    Static cachedSource As CancellationTokenSource
    Static cachedId As Long

    If ((Not cachedSource Is Nothing) AndAlso (Not cachedSource.IsCancellationRequested)) Then
        cachedSource.Cancel()
    End If

    cachedSource = New CancellationTokenSource
    cachedId += 1L

    Dim token As CancellationToken = cachedSource.Token
    Dim id As Integer = cachedId

    Task.Factory.StartNew(
        Sub()

            Dim result As IList = Nothing
            Dim [error] As Exception = Nothing
            Dim cancelled As Boolean = False

            Try

                'Background thread, do not make any UI calls.

                For Each item In list
                    '...
                    token.ThrowIfCancellationRequested(True)
                Next

                result = a_updated_list

            Catch ex As OperationCanceledException
                cancelled = True
            Catch ex As ObjectDisposedException
                cancelled = True
            Catch ex As Exception
                [error] = ex
            Finally
                If (id = cachedId) Then
                    Me.Invoke(
                        Sub()
                            If (((Not Me.IsDisposed) AndAlso (Not Me.Disposing))) Then

                               'UI thread.

                                If (Not [error] Is Nothing) Then
                                    '...
                                ElseIf (Not cancelled) Then
                                    For Each item In result
                                        '...
                                    Next
                                End If

                            End If
                        End Sub)
                End If
            End Try

        End Sub)

End Sub

VB.Net线程建议

1 个答案: