主题：[讨论]还没有选择就执行代码了

 要额外处理一下才行

http://foxtable.com/bbs/dispbbs.asp?BoardID=2&ID=69889&skin=0

是不是你文件名有问题？弹出看一下

Dim  a As String =e.Form.Controls("ComboBox1").text
Dim Book As New XLS.Book(ProjectPath & "Attachments\学籍卡.xls") '打开模板
Dim fl As String = ProjectPath & "Reports\" & a & ".pdf"
Dim Sheet As XLS.Sheet = Book.Sheets(0)
Sheet(1,9).Value = "<[班级名称] = '" & a &"'>"
Book.Build() '生成报表
msgbox(fl)
book.SaveToPDF(fl)

Dim Proc As New Process    '打开报表输出目录
Proc.File = ProjectPath & "reports"
Proc.Start()

你肯定在别的事件写有代码。selectedindexchanged不会在你没选择的时候触发的。

 那就加一个判断

Dim a As String =e.Form.Controls("ComboBox1").text
If a > "" Then
    Dim Book As New XLS.Book(ProjectPath & "Attachments\学籍卡.xls") '打开模板
    Dim fl As String = ProjectPath & "Reports\" & a & ".pdf"
    Dim Sheet As XLS.Sheet = Book.Sheets(0)
    Sheet(1,9).Value = "<[班级名称] = '" & a &"'>"
    Book.Build() '生成报表
    book.SaveToPDF(fl)
   
    Dim Proc As New Process    '打开报表输出目录
    Proc.File = ProjectPath & "reports"
    Proc.Start()
End If