如果未传递参数，如何避免vb.net中的请求查询字符串异常

Question

If the parameter variable is not passed then this code throws an exception of "Conversion from string "" to type 'Date' is not valid."

this is my code.

 Public Shared ReadOnly Property Request_projectStartDate() As Date
        Get
            Dim _value As String = Nothing

            If Not HttpContext.Current.Request.QueryString("projectStartDate") Is Nothing Then
                _value = HttpContext.Current.Request.QueryString("projectStartDate").ToString()
            End If

            Return CDate(_value)
        End Get
    End Property

Answer 1

You can check what @Massimiliano has reported and one more check

If Request.QueryString.HasKeys() Then

   // Check for specified querystrings...
   If Not String.IsNullOrEmpty(Request.QueryString("projectStartDate")) Then
       // Your logic
   End If

End If

Answer 2

If Not String.IsNullOrEmpty(Request.QueryString("projectStartDate")) Then
    //
End If

Answer 3

如果没有Request.QueryString（“ projectStartDate”）和Request.QueryString（“ projectStartDate”）<>“”然后