创建自定义异常并抛出

你可以创建自定义异常并在执行函数期间抛出它们。作为一般做法，只有在函数无法实现其定义的功能时才应抛出异常。

Private Function OpenDatabase(Byval Server as String, Byval User as String, Byval Pwd as String)
    if Server.trim="" then 
        Throw new Exception("Server Name cannot be blank")
    elseif User.trim ="" then 
        Throw new Exception("User name cannot be blank")
    elseif Pwd.trim="" then 
        Throw new Exception("Password cannot be blank")
    endif

    'Here add codes for connecting to the server
End function