GridView RowUpdating cannot change column value

I'm trying to change a column value on a gridview (.net 3.5) using the RowUpdating event. The event is fired and I set a new value - but the table is not updated.

<asp:GridView ID="GridViewHotels" runat="server" AllowSorting="True" 
        AutoGenerateColumns="False" DataSourceID="SqlDataSourceHotels" 
        OnRowUpdating="GridViewHotels_RowUpdating">

...

<asp:BoundField DataField="lat" HeaderText="lat" SortExpre开发者_如何学Gossion="lat" />

...

<asp:SqlDataSource ID="SqlDataSourceHotels" runat="server" 
               UpdateCommand="UPDATE [hotels] SET ... [lat] = @lat .... WHERE [id] = @id">

This is the event code (which is called):

    protected void GridViewHotels_RowUpdating(Object sender, 
GridViewUpdateEventArgs e)
    {
        e.NewValues["lat"] = "xxx";
    }

And yet ,the "lat" field is not updated

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What is your grid datasource bound to? If it is a dataset you're keeping in ViewState, etc, you will have to call AcceptChanges and rebind the data. If the underlying data is in a database, simply rebind the grid from the data source (after updating it), i.e. refresh it from sql server/whatever your data source is.

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I believe you need a connection string in your SQLDataSource.