似乎无法获得这个“if

似乎无法获得这个“if-statement”的权利。(Can't seem to get this “if-statement” right. Vb.net)

基本上我将一个随机行从文本框分成4个部分：代理，代理ip，如果用户提供了用户名和密码，那么它们就成了第3和第4部分。

如果用户没有提供代理凭证，并且只提供了代理IP和端口，我不希望使用代理凭据。 这是我的代码：

If SwitchButton2.Value = True Then randomline = RandomNumbers.Next(proxybox.Lines.Length) Dim s As String = proxybox.Lines(randomline) RandomProxy = Split(s, ":", , CompareMethod.Text) request.Proxy = New WebProxy(RandomProxy(0).ToString & ":" & RandomProxy(1).ToString) Try If RandomProxy(2) And RandomProxy(3) IsNot Nothing Then request.UseDefaultCredentials = False request.Proxy.Credentials = New System.Net.NetworkCredential(RandomProxy(2).ToString, RandomProxy(3).ToString) End If Catch MessageBox.Show("no credentials") End Try End If

我在这里的If语句有问题：

Try If RandomProxy(2) And RandomProxy(3) IsNot Nothing Then request.UseDefaultCredentials = False request.Proxy.Credentials = New System.Net.NetworkCredential(RandomProxy(2).ToString, RandomProxy(3).ToString) End If Catch MessageBox.Show("no credentials") End Try

我每次都会抛出异常，我做错了什么？ 我只希望在提供代理凭证时使用它们，如果没有则继续使用。

Basically I am splitting up a random line from a text box into 4 parts: a proxy, the proxy ip, and if the user has supplied a username and password those become parts 3 and 4.

I don't want the proxy credentials to be used if the user has not supplied them, and has only supplied the proxy ip and port. Here is my code:

If SwitchButton2.Value = True Then randomline = RandomNumbers.Next(proxybox.Lines.Length) Dim s As String = proxybox.Lines(randomline) RandomProxy = Split(s, ":", , CompareMethod.Text) request.Proxy = New WebProxy(RandomProxy(0).ToString & ":" & RandomProxy(1).ToString) Try If RandomProxy(2) And RandomProxy(3) IsNot Nothing Then request.UseDefaultCredentials = False request.Proxy.Credentials = New System.Net.NetworkCredential(RandomProxy(2).ToString, RandomProxy(3).ToString) End If Catch MessageBox.Show("no credentials") End Try End If

I am having trouble with the If statment here:

Try If RandomProxy(2) And RandomProxy(3) IsNot Nothing Then request.UseDefaultCredentials = False request.Proxy.Credentials = New System.Net.NetworkCredential(RandomProxy(2).ToString, RandomProxy(3).ToString) End If Catch MessageBox.Show("no credentials") End Try

I am getting the exception thrown everytime, what am i doing wrong with it? I only want the proxy credentials to be used if they are supplied and continue on if not.

最满意答案

您需要分别测试每个值：

If RandomProxy(2) IsNot Nothing AndAlso RandomProxy(3) IsNot Nothing Then

您还应该在尝试使用它们之前测试数组中是否存在足够的元素：

If RandomProxy IsNot Nothing AndAlso RandomProxy.Length >= 4 AndAlso RandomProxy(2) IsNot Nothing AndAlso RandomProxy(3) IsNot Nothing Then

最后

You need to test each of the values separately:

If RandomProxy(2) IsNot Nothing AndAlso RandomProxy(3) IsNot Nothing Then

You should also test to see if enough elements exist in the array prior to attempting to use them:

If RandomProxy IsNot Nothing AndAlso RandomProxy.Length >= 4 AndAlso RandomProxy(2) IsNot Nothing AndAlso RandomProxy(3) IsNot Nothing Then

and finally