如何处理 VBA 中的网络异常？

Question

    Sub test()

    Dim id As String
    id = "user1234"
    Dim PHARMA As String
    PHARMA = "http://xxxx"
    Dim url As String
    url = PHARMA & id


    Dim IE As MSXML2.XMLHTTP60
    Set IE = New MSXML2.XMLHTTP60

    IE.Open "GET", url, False
    IE.send

    'This part could crash the program crash if the user 
    'or the url is wrong, how can I handle this case with exceptions?  

    While IE.readyState <> 4
        DoEvents
    Wend

    Dim HTMLDoc As MSHTML.HTMLDocument
    Dim HTMLBody As MSHTML.HTMLBody

    Set HTMLDoc = New MSHTML.HTMLDocument

    ...

    End Sub

这里是我输入错误的ID或者url

当我进入 chrome 网络选项卡时：

Cache-Control:no-cache
Content-Length:0
Date:Tue, 25 Oct 2016 15:22:04 GMT
Expires:-1
Pragma:no-cache
Server:Microsoft-IIS/7.0

当我进入答案选项卡时，我有：

请求没有可用的响应数据（正常是因为url或id错误）

如何处理 VBA 中的网络异常？

Answer 1

我假设您在 .Send 调用后不需要 IE 对象并继续处理 HTMLDocument 对象：

Private Function TryHttpGet(ByVal url As String) As MSHTML.HTMLDocument
    On Error GoTo CleanFail
    Dim document As MSHTML.HTMLDocument        

    With New MSXML2.XMLHTTP60
        .Open "GET", url, False
        .Send

        'not needed per comment: 
        'While .ReadyState <> 4 'todo: replace magic value with meaningful constant
        '    DoEvents
        'Wend

        'Set document = ...

    End With

CleanExit:
    'cleanup code here?
    Set TryHttpGet = document
    Exit Sub

CleanFail:
    'error-handling code here
    Set document = Nothing
    Resume CleanExit
End Sub

然后调用代码可以这样做：

Set document = TryHttpGet(url)
If document Is Nothing Then
    MsgBox "HTTP request failed for URL: " & url & ".", vbExclamation
    Exit Sub
End If