Dim Result in functions??

Question

how am I supposed to declare the "result variable in a function

I havnt been able to find any examples of functions, only subs and in those there is usually a "result" variable initially set = ""

I've modified this logic for my functions but dont understand why the result is set to = "" and not delared as the same data type as the funtion e.g

Public Shared Function fncParamNumber(UID As Integer, UserID As String) As Decimal
        Dim result As Decimal
        Try
            Using ws As New LightSwitchApplication.DataWorkspace()
                Dim param = (From x In ws.Tech_MembersData.tbl_UPV_UserParamValues
                            Where x.UPV_UserParamUID = UID AndAlso x.UPV_UserUID = UserID
                            Select x).FirstOrDefault()
                If (param Is Nothing) Then
                    result = Nothing
                Else
                    result = param.UPV_ValueNumeric
                End If
            End Using
        Catch ex As Exception
            result = ex.Message
        End Try
        fncParamNumber = result
    End Function

Problem with this function is its not trapping exceptiosn proerly as I have declared the Result as a decimal, but if htere is an exception its going to crap out.

How are you supposed to handle the exceptions ?

Thanks

Grant

Answer 1

Wrong forum for this kind of thing, but for Functions in VB you either:

Return x
(where x is the variable you want the function to return)
or
fncParamNumber = x
(where you set the name of the function to be the result you want to return)

You probably want to return "Nothing" if there's an exception, and whatever is calling the function should check for it.

Where are you expecting the exception to occur?

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Free Visual Studio LightSwitch extensions: Elyl's Extensions http://visualstudiogallery.msdn.microsoft.com/bbe013bf-45b6-46c4-ba13-537cc23c5118

Answer 2

If you need to return two different values back from a function, there are two basic ways to do it:

• Make the return value a complex class that consists of the two (or more) properties that you need to return, usinmg a result class:
  

Public Class ComplexResult
    Public Property Value as Decimal?
    Public Property Error as String
End Class

Public Shared Function fncParamNumber(UID As Integer, UserID As String) As ComplexResult
    Dim result As ComplexResult
    result.Value = Nothing
    result.Error = ""
    
    Try
        Using ws As New LightSwitchApplication.DataWorkspace()
            Dim param = ( _
                From x In ws.Tech_MembersData.tbl_UPV_UserParamValues
                Where x.UPV_UserParamUID = UID AndAlso x.UPV_UserUID = UserID
                Select x).FirstOrDefault()
                
            If (param IsNot Nothing) Then
                result.Value = param.UPV_ValueNumeric
            End If
        End Using
        
    Catch ex As Exception
        result.Error = ex.Message       
    End Try
    
    return result
End Function

You'll notice that I changed your line "fncParamNumber =result" to "return result". Setting the function's name equal to the return value is the "old" way (pre .NET) of returning values. .NET introduced the ability to "Return" a result.

• The other way that you can return more than one value uses ByRef parameters to store the values:

Public Shared Function fncParamNumber(UID As Integer, UserID As String, ByRef ErrorMessage as string) As Decimal
    Dim result As Decimal = 0D

    ErrorMessage = ""

    Try
        Using ws As New LightSwitchApplication.DataWorkspace()
            Dim param = ( _
                From x In ws.Tech_MembersData.tbl_UPV_UserParamValues
                Where x.UPV_UserParamUID = UID AndAlso x.UPV_UserUID = UserID
                Select x).FirstOrDefault()
               
            If (param IsNot Nothing) Then
                result = param.UPV_ValueNumeric
            End If
        End Using
       
    Catch ex As Exception
        ErrorMessage = ex.Message      
    End Try
   
    return result
End Function

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Yann - LightSwitch Central - Click here for FREE Themes, Controls, Types and Commands

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Answer 3

Thanks Yann, you have answered my question and more...now I can have one function to retrieve, text, numeric or date values from my parameter table!

Will have a play with this once I get LS workin again!

Cheers

Grant

Answer 4

You're welcome.

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Yann - LightSwitch Central - Click here for FREE Themes, Controls, Types and Commands

If you find a reply helpful, please click "Vote as Helpful", if a reply answers your question, please click "Mark as Answer"

By doing this you'll help people find answers faster.