从 Web 检索数据的时间循环 - VB.NET

Question

我使用以下方法成功地从 Web 检索数据：

Dim webClient As New System.Net.WebClient
Dim result As String = webClient.DownloadString("http://www.example.org")
Dim o As Object
Dim dizi As String() = result.Split(New String() {",,,"}, StringSplitOptions.None)
' urls on the webpage are seperated with ,,, so it gets the first website
Dim urladdress As String = dizi(0)
o.Navigate2(urladdress)

但是，我需要为它添加时间循环。例如，它需要每 5 分钟检索一次数据。尝试了这个没有任何运气：

Imports System.Timers
Public Class TimerRequest
    Private Shared aTimer As Timer
    Private Shared o as Object
        Public Shared Sub Main()
             aTimer = New System.Timers.Timer(300000) ' 5 minutes
             AddHandler aTimer.Elapsed, AddressOf OnTimedEvent
             aTimer.Enabled = True
        End Sub  
        Private Shared Sub OnTimedEvent(source As Object, e As ElapsedEventArgs)
'----------------------------------------
    Dim webClient As New System.Net.WebClient
    Dim result As String = webClient.DownloadString("http://www.example.org")
    Dim o As Object
    Dim dizi As String() = result.Split(New String() {",,,"}, StringSplitOptions.None)
    ' urls on the webpage are seperated with ,,, so it gets the first website
    Dim urladdress As String = dizi(0)
    o.Navigate2(urladdress)
'----------------------------------------
        End Sub  
 End Class  

这些是错误

！[在此输入图像描述][1]

正确的方法是什么？

Answer 1

我会使用Microsoft的响应式框架（NuGet "Rx-Main"）来做到这一点。

以下是您需要的全部代码量：

Dim subscription = _
    Observable _
        .Interval(TimeSpan.FromMinutes(5.0)) _
        .StartWith(-1L) _
        .SelectMany( _
            Observable _
                .Using( _
                    Function() New WebClient(), _
                    Function(wc) _
                        wc.DownloadStringTaskAsync("http://www.example.org") _
                            .ToObservable())) _
        .Select(Function(result) _
            result.Split(New String() {",,,"}, StringSplitOptions.None)(0)) _
        .Subscribe(Sub(urladdress) o.Navigate2(urladdress))

这将自动下载您的页面并每 5 分钟解析一次urladdress。

好消息是您可以拨打subscription.Dispose()关闭订阅。

Answer 2

您可以在循环中尝试 Sleep 方法吗？

For i = 1 To 5 
System.Threading.Thread.Sleep(300000) '// 5 mins in milliseconds
'// Do Something
Next i