Conversion from type 'DBNull' to type 'String' is not valid. clickable data

Question

I'm a newbie to aspx programming. I'm facing the problem where the data I fetch contain null value. my code :

<asp:TemplateField HeaderText="NCRE" ItemStyle-Width="150px" >
    <ItemTemplate>
        <asp:Hyperlink ID="Hyperlink1" runat="server"  Text='<%# Eval("formid") %>' NavigateUrl='<%# Eval("formid","~/sapphire/ncrr" + Mid(Eval("formid"), 4, 1) + ".aspx?formid={0}") %>' />
    </ItemTemplate>
</asp:TemplateField>

And my code behind:

Protected Function geturl(value As Object) As String
    Dim NCRE As String = Convert.ToString("formid")
    If Mid(NCRE, 4, 1) = 2 Then
        Return ("~/sapphire/ncrr2.aspx")
    Else
        Return ("~/sapphire/ncrr1.aspx")
    End If
End Function

im using gridview to pull the data out and display it on table — Joe Cheong, Aug 17 '15 at 07:36
And that doesn't yield any result I guess for that specific ID? — Patrick Hofman, Aug 17 '15 at 07:38
i have pulled out the result is just that some of the data in between is null — Joe Cheong, Aug 17 '15 at 07:40
nothing happen becoz the un"null" data can be lickable to the following link i have shown in code behind. and i get the error as the title above. — Joe Cheong, Aug 17 '15 at 07:43
Does this help you? http://stackoverflow.com/q/1979806/993547 — Patrick Hofman, Aug 17 '15 at 07:44
i still don`t understand how do i fix my problem after i see the link u sent to me. sorry =( i`m a newbie so my understanding is quite limited . — Joe Cheong, Aug 17 '15 at 08:07
Copy that method in your code file and use it in the evaluation to make sure it doesn't return `DbNull` but a valid `string`, like `null`. — Patrick Hofman, Aug 17 '15 at 08:08
@JoeCheong You can use the [COALESCE](https://msdn.microsoft.com/en-us/library/ms190349%28v=sql.100%29.aspx) function in SQL to change NULLs to something else, e.g. `SELECT col1, col2, COALESCE(col3, 'text to say it is blank') FROM ...`. — Andrew Morton, Aug 17 '15 at 09:03

score 1 · Answer 1 · edited May 23 '17 at 10:26

To help you getting the right code from the post I've linked:

Copy this part into your code file (ending on aspx.cs):

Public Function ProcessMyDataItem(myValue As Object) As String
    If myValue Is Nothing OrElse myValue = DbNull.Value Then
        Return "(no value)"
    End If

    Return myValue.ToString()
End Function

And in your .aspx:

<asp:TemplateField HeaderText="NCRE" ItemStyle-Width="150px" >
    <ItemTemplate>
        <asp:Hyperlink ID="Hyperlink1" runat="server"  Text='<%# ProcessMyDataItem(Eval("formid")) %>' NavigateUrl='<%# Eval("formid","~/sapphire/ncrr" + Mid(ProcessMyDataItem(Eval("formid")), 4, 1) + ".aspx?formid={0}") %>' />
    </ItemTemplate>
</asp:TemplateField>

@PatrickHofman Original answer was in the wrong language. Removed based upon the update. — duffn, Aug 18 '15 at 01:13

score 0 · Answer 2 · answered Aug 17 '15 at 08:53

0

You can use IIf (IIf(IsDBNull(Eval("fieldName")) = True, *do what You want when record is empty*, *do what You want when record isn't empty)).

There are examples :

Text = '<%# IIf(IsDBNull(Eval("formid")) = True, "no data", Eval("formid))%>'

Same code You can use for NavigateUrl :

NavigateUrl = '<%# IIf(IsDBNull(Eval("formid")) = True, "#", Eval("formid","~/sapphire/ncrr" + Mid(Eval("formid"), 4, 1) + ".aspx?formid={0}"))'

And, then, in Your function geturl (code behind) first check is value, for example # (do nothing, or just return empty), otherwise execute code.

answered Aug 17 '15 at 08:53

nelek

4,074
3
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You may be interested in the [If Operator](https://msdn.microsoft.com/en-us/library/Bb513985%28v=vs.120%29.aspx). – Andrew Morton Aug 17 '15 at 08:58
@AndrewMorton yes, `If` can be used too. – nelek Aug 17 '15 at 09:02
Overload resolution failed because no accessible 'IIf' accepts this number of arguments..i got this error > – Joe Cheong Aug 18 '15 at 01:33
@JoeCheong I suggest that you forget you ever heard of "Iif". It has [gotchas](http://stackoverflow.com/a/1220416/1115360). – Andrew Morton Aug 18 '15 at 10:30

score 0 · Answer 3 · answered Aug 18 '15 at 02:44

0

You may only add an empty string to avoid the error:

Dim NCRE As String = Convert.ToString("formid") & ""

Or, to avoid error at the 4th position:

Dim NCRE As String = Convert.ToString("formid") & " "

answered Aug 18 '15 at 02:44

David BS

1,822
1
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35

Conversion from type 'DBNull' to type 'String' is not valid. clickable data

3 Answers3