如何在vb.net中等待不再有来自weblient的"404“？

Dim client As New WebClient()
AddHandler client.DownloadStringCompleted, AddressOf WebClient_DownloadStringCompleted

Private Sub WebClient_DownloadStringCompleted(sender As Object, e As DownloadStringCompletedEventArgs)
    If e.Error IsNot Nothing AndAlso e.Error.GetType() Is GetType(WebException) Then
        Dim webEx As WebException = DirectCast(e.Error, WebException)
        Dim response As HttpWebResponse = DirectCast(webEx.Response, HttpWebResponse)
        
        If response IsNot Nothing AndAlso response.StatusCode = HttpStatusCode.NotFound Then
            ' 处理"404"错误
        Else
            ' 处理其他错误
        End If
    Else
        ' 处理请求成功的情况
    End If
End Sub