索引超出范围-必须为非负数并且小于集合的大小

Question

我正在为此使用GridView模板字段。我想更新“权限”列中的数据。但是我收到错误消息“索引超出范围。必须为非负数，并且小于集合的大小。参数名称：index”

下面是后端代码。

protected void gvRequestStatus_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            try
            {
                using (SqlConnection con = db.ConnectToDb())
                {
                    con.Open();
                    string query = "UPDATE Shipment SET Permission=@status WHERE ShipmentID=@id;";
                    SqlCommand cmd = new SqlCommand(query, con);
                    cmd.Parameters.AddWithValue("@status", (gvRequestStatus.Rows[e.RowIndex].FindControl("ddlPermission") as DropDownList).SelectedIndex.ToString());
                    cmd.Parameters.AddWithValue("@id", (gvRequestStatus.DataKeys[e.RowIndex].Value.ToString()));
                    cmd.ExecuteNonQuery();

                    lblSuccessMessage.Text = "Status Updated";
                    lblErrorMessage.Text = "";
                    gvRequestStatus.EditIndex = -1;
                    PopulateGridView();
                }
            }
            catch (Exception ex)
            {
                lblSuccessMessage.Text = "";
                lblErrorMessage.Text = ex.Message;
            }
        }

我在哪里做错了？

以下是前端（gridview）代码

<asp:GridView ID="gvRequestStatus" runat="server" Width="85%" EmptyDataText="No Record Found" CssClass="gvCss" HeaderStyle-CssClass="header-center" AutoGenerateColumns="False" OnRowCommand="gvRequestStatus_RowCommand" OnRowEditing="gvRequestStatus_RowEditing" OnRowCancelingEdit="gvRequestStatus_RowCancelingEdit" OnRowUpdating="gvRequestStatus_RowUpdating">
                <Columns>
                    <asp:TemplateField HeaderText="Shipment ID">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("ShipmentID") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Departing Port">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("DepartPort") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Arriving Port">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("ArrivalPort") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Requested Date">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("RequestDate") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Remarks">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("Remarks") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Status">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("Permission") %>'></asp:Label>
                        </ItemTemplate>
                        <EditItemTemplate>
                            <asp:DropDownList ID="ddlPermission" Text='<%#Eval("Permission") %>' runat="server">
                                <asp:ListItem Text="Pending" Value="Pending"/>
                                <asp:ListItem Text="Approved" Value="Approved"/>
                                <asp:ListItem Text="Rejected" Value="Rejected"/>
                                <asp:ListItem Text="Shipping" Value="Shipping"/>
                                <asp:ListItem Text="Delivered" Value="Delivered"/>
                            </asp:DropDownList>

                        </EditItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Cost">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("Cost") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="User ID">
                        <ItemTemplate>
                            <asp:Label runat="server" Text='<%#Eval("UserID") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField >
                        <ItemTemplate>
                            <asp:ImageButton runat="server" ImageUrl="~/Pics/edit.png" CommandName="Edit" ToolTip="Edit" width="20px" Height="20px"/>
                            <%--<asp:ImageButton runat="server" ImageUrl="~/Pics/delete.png" CommandName="Delete" ToolTip="Delete" width="20px" Height="20px"/>--%>
                        </ItemTemplate>
                        <EditItemTemplate>
                            <asp:ImageButton runat="server" ImageUrl="~/Pics/save.png" CommandName="Update" ToolTip="Edit" width="20px" Height="20px"/>
                            <asp:ImageButton runat="server" ImageUrl="~/Pics/cancel.png" CommandName="Cancel" ToolTip="Cancel" width="20px" Height="20px"/>
                        </EditItemTemplate>
                    </asp:TemplateField>
                </Columns>
                <HeaderStyle HorizontalAlign="Center" />
                <rowstyle Height="40px"/>

            </asp:GridView>