如何取消异步回调?

[weberli]

代码如下：

    Public Sub RefreshText()
        Dim handler As New EditData.ReadvalueDelegate(AddressOf EditData.Readvalue)
        Dim result As IAsyncResult = handler.BeginInvoke(ConSQL, Constr, New AsyncCallback(AddressOf ReadValueComplete), handler)
    End Sub
 Private Sub ReadValueComplete(ByVal result As IAsyncResult)
        Dim handler As EditData.ReadvalueDelegate = DirectCast(DirectCast(result, AsyncResult).AsyncDelegate, EditData.ReadvalueDelegate)
        setText(handler.EndInvoke(result).ToString())
    End Sub
    Public Delegate Sub SetTextCallback(ByVal Value As String)
    ' 设置文本函数
    Private Sub setText(ByVal Value As String)
        If Me.InvokeRequired Then
            Dim s As New SetTextCallback(AddressOf setText)
            Invoke(s, New String() {Value})
        Else
            Me.Text = "有" & Value & Destrip
            Compelete = True
        End If
    End Sub

以上代码是异步回调，现在我想增加取消异步回调

[兔子-顾问]

只能在方法内部关键点写判断，比如设置某个变量，suspend_call，如果为true则返回不继续执行。