CODEWITHSUNDEEP
asp.netvb.net
StrattonL
StrattonL

Reputation: 726

Checking whether value is DBNull

I have the following function:

Public Shared Function imageExists(ByVal path As Object) As Boolean
                If IsDBNull(path) = False Or Not path Is Nothing Then
                    Dim pathString As String = Convert.ToString(path)
                    If Exists(HttpContext.Current.Server.MapPath(path)) Then
                        Return True
                    Else
                        Return False
                    End If
                Else
                    Return False
                End If

            End Function

Called by the visible property for this image control:

<asp:Image ID="img_SmallImage" runat="server" ImageUrl='<%# "~/Content/Images/Exclusive/" + Eval("trip_SmallImage") %>' Visible='<%# OnTheMain.Images.Validation.imageExists(Eval("trip_SmallImage"))%>' />

No matter what I try for the If IsDBNull part, it either ignores it and executes the code, or returns an error such as Conversion from type 'DBNull' to type 'String' is not valid.

How can I rectify the situation?

Upvotes: 0

Views: 377

Answers (3)

Edwin
Edwin

Reputation: 1468

Use 

If Not String.IsNullOrEmpty(path) Then

as you need to handle empty strings. You should be passing a String, not a generic Object. Also, you can't do Or Not Nothing. You would have to do Not IsDBNull(path) And Not path Is Nothing.

Upvotes: 0

Alaa Alweish
Alaa Alweish

Reputation: 9084

I don't know why you are using both IsDBNull and Nothing, anyway

Use AndAlso, it will not check the next part if previous is false

check the path first to prevent the exception: 

        If path IsNot Nothing AndAlso IsDBNull(path) = False Then
        'do what ever you want to do
    End If

FYI, OrElse will do the same function for Or, for me i am using this short-circuiting logical operators by default read my question on this here

Upvotes: 1

Mike Corcoran
Mike Corcoran

Reputation: 14565

you have a logical error in the first if check.

Not Nothing always evaluates to true. so that first statement basically compiles down to:

If IsDBNull(path) Or True Then

which will always be true. your if statement should probably look like this:

If Not IsDBNull(path) And path Is Not Nothing Then

Upvotes: 2

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