Gridview - index range exception when looping through rows

Question

I have a problem with a exception below:

index out of range

I have a GridView where each row has a CheckBox. When I select and item in a DropDown list a certain action is performed depending on the ListItem value.

protected void actionSelect_SelectedIndexChanged(object sender, EventArgs e)
{       
    GridView gv = Project_GridView;

    DropDownList ddl = (DropDownList)sender;
    int SelectValue = Convert.ToInt32(ddl.SelectedValue);
    UpdateOp(gv, SelectValue);
    dl_actionSelect.SelectedIndex = 0;
    DataBind();
}

This code is run:

private void UpdateOp(GridView gv, int SelectValue)
{
    foreach (GridViewRow row in gv.Rows)
    {
        CheckBox check = (CheckBox)row.FindControl("CB_ActionSelect");
        if (check.Checked)
        {
            int rowIndex = row.RowIndex;               
            DataBind();              
            if (!(DBNull.Value == gv.DataKeys[row.RowIndex].Value)) //This line throws the exception
            {
                int original_id = Convert.ToInt32(gv.DataKeys[row.RowIndex].Value);                   
                //Op_Update
                uWeb.Data.ProjLines.Op_Update(SelectValue, original_id);
            }
        }
    }
} 

Loops through rows and finds the checked ones. However when more than one checkbox is selected I get:

ArgumentOutOfRangeException: Index is out of range

And the weird part is it seems to be random amount that can successfully run. 1 checked always works, 2+ is rather random sometimes it works sometimes it doesn't. Something with the id for the control?

GridView:

<asp:GridView ID="Project_GridView" runat="server" SkinID="ProdView" 
      AutoGenerateColumns="False" DataKeyNames="ROWNUMBER" CssClass="gvv"
      DataSourceID="Project_ObjectDataSource" OnRowDataBound="Project_GridView_RowDataBound"
      AllowSorting="true" Width="100%" AlternatingRowStyle-BackColor="LightGray">
    <Columns>
        <asp:TemplateField HeaderText="" ItemStyle-Width="4%">
            <ItemTemplate>
                <asp:CheckBox id="CB_ActionSelect" Text="" runat="server"/>
            </ItemTemplate>                                
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Answer 1

You should get it like this:

string Id = gv.DataKeys[row.RowIndex %= gv.PageSize][0].ToString();

Because, the reported error occurs when the GridView's index increases from the row count.