下拉列表（编辑网格视图）中选定项目的值返回 NULL。它应该返回选定的值..
aspx.cs 文件中的代码::
GridViewRow row = (GridViewRow)GridView1.Rows[e.RowIndex];
DropDownList ct = (DropDownList)row.FindControl("DropDownList6");
string ctype = ct.SelectedItem.Text;
string sql1 = ("Select Case_Type_Value FROM Case_Type where Case_Type_Text ='" + ctype + "' ");
DropDownList cs = (DropDownList)row.FindControl("DropDownList3");
string cstatus = cs.SelectedItem.Text;
string sql2 = ("Select Case_Status_Value FROM Case_Status where Case_Status_Text ='" + cstatus + "' ");
SqlConnection con= new SqlConnection(ConfigurationManager.ConnectionStrings["con"].ToString());
SqlCommand cmd1 = new SqlCommand(sql1, con);
SqlCommand cmd2 = new SqlCommand(sql2, con);
con.Open();
int v1 = Convert.ToInt32(cmd1.ExecuteScalar());
int v2 = Convert.ToInt32(cmd2.ExecuteScalar());
con.Close();
SqlCommand cmd = new SqlCommand("UPDATE Table SET Case_Type = @Case_Type, Case_Status = @Case_Status, con);
cmd.Parameters.AddWithValue("@Case_Type", v1);
cmd.Parameters.AddWithValue("@Case_Status", v2);
下面是页面的aspx代码：
<asp:GridView ID="GridView1" runat="server" CellPadding="5" ForeColor="#333333" width="1000px"
GridLines="None" OnPageIndexChanging="gridView_PageIndexChanging"
AllowSorting="True" OnSorting="gridView_Sorting" AutoGenerateColumns="False" OnRowUpdating="GridView1_RowUpdating"
BorderStyle="Outset" CellSpacing="1" Font-Names="Cambria"
Font-Size="Small" AllowPaging="True" ShowFooter="True"
ShowHeaderWhenEmpty="True"
DataSourceID="SqlDataSource1" onselectedindexchanged="GridView1_SelectedIndexChanged"
>
<AlternatingRowStyle BackColor="White" ForeColor="#284775" />
<Columns>
<asp:TemplateField HeaderText="Case Number" SortExpression="case_number">
<EditItemTemplate>
<asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("case_number") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label7" runat="server" Text='<%# Bind("case_number") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Case Name" SortExpression="case_name">
<EditItemTemplate>
<asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("case_name") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label8" runat="server" Text='<%# Bind("case_name") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Case Type" SortExpression="Case_Type_Text">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList6" runat="server"
DataSourceID="SqlDataSource2" DataTextField="Case_Type_Text"
DataValueField="Case_Type_Text" SelectedValue='<%# Bind("Case_Type_Text") %>'>
<asp:ListItem>--Select--</asp:ListItem>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label9" runat="server" Text='<%# Bind("Case_Type_Text") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Case Status" SortExpression="Case_Status_Text">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList3" runat="server"
DataSourceID="SqlDataSource3" DataTextField="Case_Status_Text" DataValueField="Case_Status_Text"
SelectedValue='<%# Bind("Case_Status_Text") %>'>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("Case_Status_Text") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Assigned Date" SortExpression="assigned_date">
<EditItemTemplate>
<asp:TextBox ID="TextBox5" runat="server"
Text='<%# Bind("assigned_date", "{0:d}") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label10" runat="server"
Text='<%# Bind("assigned_date", "{0:d}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Assigned To" SortExpression="assigned_to">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList7" runat="server"
DataSourceID="SqlDataSource4" DataTextField="User_Name"
DataValueField="User_Name" SelectedValue='<%# Bind("assigned_to") %>'>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label11" runat="server" Text='<%# Bind("assigned_to") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Date Withdrawn" SortExpression="date_withdrawn">
<EditItemTemplate>
<cc1:DatePicker ID="DatePicker5" runat="server" DateFormat="yyyy-MM-dd"
CalendarDate='<%# Bind("date_withdrawn") %>' TextCssClass="" />
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label4" runat="server"
Text='<%# Bind("date_withdrawn", "{0:d}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Date Delivered" SortExpression="date_delivered">
<EditItemTemplate>
<cc1:DatePicker ID="DatePicker7" runat="server"
CalendarDate='<%# Bind("date_delivered") %>' TextCssClass=""
/>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label6" runat="server"
Text='<%# Bind("date_delivered", "{0:d}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="QC By" SortExpression="qc_by">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList5" runat="server"
DataSourceID="SqlDataSource4" DataTextField="User_Name" DataValueField="User_Name"
SelectedValue='<%# Bind("qc_by") %>'>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("qc_by") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="QC Date" SortExpression="qc_date">
<EditItemTemplate>
<cc1:DatePicker ID="DatePicker6" runat="server"
CalendarDate='<%# Bind("qc_date") %>' TextCssClass=""
/>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label5" runat="server" Text='<%# Bind("qc_date", "{0:d}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Additional Notes">
<EditItemTemplate>
<asp:TextBox ID="TextBox1" runat="server"
Text='<%# Bind("additional_notes") %>' TextMode="MultiLine"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label3" runat="server" Text='<%# Bind("additional_notes") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:CommandField ShowEditButton="True" ButtonType="Button"
CausesValidation="False" />
</Columns>
<EditRowStyle BackColor="#999999" />
<FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
<RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
<SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
<SortedAscendingCellStyle BackColor="#E9E7E2" />
<SortedAscendingHeaderStyle BackColor="#506C8C" />
<SortedDescendingCellStyle BackColor="#FFFDF8" />
<SortedDescendingHeaderStyle BackColor="#6F8DAE" />
</asp:GridView>