Passing exceptions from DLL to ASPX page?

[NBartomeli]

I have a dll (report.vb) file that i pass a dataset to so it will get filled. In the routine, if the dataset exceedes a certain number of rows or columns, I want it to throw an exception and exit before it goes back to the page.

I have the following code

reports.vb:

if rows > 255 or cols > 255 then
     Throw New System.Exception("Rows / Cols exceeded")
endif

report.aspx:

try
  dsReportData = buildReportData()
catch ex as exception
   'handle exception
finally
   ...
end try

When I step through the code, it sees the exception, then just continues on with the function and is never caught. Am I doing something wrong?

Thanks in advance for any help.

 

[ca8msm]

You don't necessarily have to throw an exception - you could do something very similar using a boolean value. For Example,

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If DoSomething(300) = True Then
            ' the number was too large
        Else
            ' the number was OK
        End If
    End Sub

    Private Function DoSomething(ByVal MyValue As Integer) As Boolean
        If MyValue > 255 Then
            Return True
        Else
            Return False
        End If
    End Function

Obviously I'm not looping through a DataSet but it should give you an example of what I'm trying to explain.

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[NBartomeli]

I appreciate your input,

However, the function must return a dataset, so I cannot have it return a boolean at the same time

I am also interested in learning how exceptions are used in this case.

thanks anyway, I appreciate it.

 

[ca8msm]

Hmmm - I tried a simple example:

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Try
            DoSomethingElse()
        Catch ex As Exception
            Response.Write(ex.StackTrace)
        End Try

    End Sub
    Private Function DoSomethingElse()
        Dim i As Integer = 1
        Throw New System.Exception("Rows / Cols exceeded")
        Dim j As Integer = 1
    End Function

When my exception is thrown, it exits the function, writes out the error and therefore "j" doesn't get set.

Are you saying that yours doesn't have this behaviour?

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[NBartomeli]

Yes, thank you

My trouble was I was trying to throw an exception back from the function inside a try/catch block. So the exception was never leaving the function, it was getting caught in the function itself and not returning to the page.

I fixed it, thank you for your input.

 

[ca8msm]

Ahh I see - it's nearly always (sometimes it isn't) best practice to have your Try/Catch in the calling function as opposed to the function itself then you can catch those errors and you know that an error occured in the function - otherwise, as you found out, the error will just be handled and your original function will carry on as normal.

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[NBartomeli]

Yeah. That is the best way, but I called the function from the ASPX page, which had a try-catch block to trap errors in the functions that it called. (does that make sense?) I just ended up having too many functions calling too many functions with 1 too many try-catch blocks in the mix.

I think I need to re-work my logic :-D

Thanks again