狐友们，我设计了一个发送邮件窗口（如图）
此主题相关图片如下：qq图片20151126155203.png
窗口中的发送按钮代码如下：
Dim cb1 As String = e.Form.Controls("combobox1").value
Dim cb2 As String = e.Form.Controls("combobox2").value
Dim tb2 As String = e.Form.Controls("textbox2").value
Dim tb3 As String = e.Form.Controls("textbox3").value
Dim tb4 As String = e.Form.Controls("textbox4").value
Dim m As New MailSender
m.Host = "mail.btte.net"
m.Account = "fsxmtidc"
m.Password = "*******"
m.From = "fsxmtidc@btte.net"
m.To = cb1
m.To = cb2
m.Title = tb2
m.Content = tb3
m.AddAttachments(tb4)
m.SendAsync()
请问如何防止提示空值，例如抄送文本框为空就提示了或者附件为空也提示空值错误，请问如何解决？？
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Post By：2015/11/26 16:12:00 [只看该作者]
