Data type conversion

sophia · February 6th, 2010, 03:49 PM

Hello Everyone,
I am trying out to fetch the Id of the item using ListView but it reports conversion error as Conversion from string "" to type 'Integer' is not valid.
the code snippet is as follows

Code:

Protected Sub ListView1_ItemCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ListViewCommandEventArgs) Handles ListView1.ItemCommand
        con.Open()
        If e.CommandName = "Play" Then
            Dim Id As Integer = ListView1.DataKeys(e.CommandArgument).Values("Id")
End If
End Sub

But the same method for fetching Id with Gridview works fine.

Code:

Protected Sub GridView1_RowCommand1(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles GridView1.RowCommand
        con.Open()
If e.CommandName = "play" Then
            Dim Id As Integer = GridView1.DataKeys(e.CommandArgument).Values("Id")
End If
End Sub

I don't know about how to cast it properly.
Any suggestion is appreciated.
Thank You.

philip_cole · February 7th, 2010, 03:31 PM

Hi Sophia,

The actual error is saying that it is trying to convert an Id value with an empty string to an integer. If they have clicked a Play button on an item, I would assume that the item would have a proper ID associated with it.
So firstly, check that you set the DataKeyNames property up on the ListView. Otherwise the control will not store the Id as a DataKey.

Secondly, you should probably check for empty IDs anyway, as best practice. A simple check along with an explicit CInt call like this should suffice:

vb Code:

If e.CommandName = "play"
    AndAlso Not String.IsNullOrEmpty(GridView1.DataKeys(e.CommandArgument).Values("Id"))
Then
        Dim Id As Integer = CInt(GridView1.DataKeys(e.CommandArgument).Values("Id"))
End If

HTH
Phil

sophia · February 8th, 2010, 03:11 AM

Hi philip,
Thanks for the reply.
I did the same as you mentioned your reply

Code:

If e.CommandName = "play"
    AndAlso Not String.IsNullOrEmpty(ListView1.DataKeys(e.CommandArgument).Values("Id"))
Then
        Dim Id As Integer = CInt(GridView1.DataKeys(e.CommandArgument).Values("Id"))
End If

On debugging I find the same error on the first line but when I delete the items by fetching the Id of items then it works fine. It means Ids are being stored properly.
Code snippet for deleting is

Code:

Protected Sub ListView1_ItemDeleting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ListViewDeleteEventArgs) Handles ListView1.ItemDeleting
        con.Open()
        Dim videoId As Integer = ListView1.DataKeys(e.ItemIndex).Values("Id").ToString()
' Some other code
con.close()
End Sub

Now can you please specify the error in the case of play command.
I've DataKeyNames set to Id in Listview
Thank you once again for reply.

sophia · February 11th, 2010, 12:29 PM

Hi, I am still having the problem in the same context, please give some suggestions regarding the topic.
Thanks...

sophia · February 14th, 2010, 03:20 AM

Hello Imar Sir, I am having some problem as mentioned in the first post. Though someone suggested solution but that is not working.
Please try to have a look on the problem.
Thank you...

Imar · February 14th, 2010, 07:36 PM

Hi sophia,

As I suggested before, please try to post this in an appropriate forum here at p2p.wrox.com. Your code is not specific to this book; in fact, you're using .NET 3.5 while the book targets 2.0. You'll get better responses if you choose the right forum *and* provide more details about your code, database setup and so on.

Cheers,

Imar