Calendar Extender SelectedDate Null

I have a calendar extender "addHoliday", but every time I select a value and try to retrieve that value in the code behind it's null. I'm not sure why this would be.

TABLE

<asp:Table runat="server">
        开发者_开发技巧        <asp:TableRow>
                    <asp:TableHeaderCell HorizontalAlign="Left">Day:</asp:TableHeaderCell><asp:TableCell>
                <asp:DropDownList ID="ddlAddDay" runat="server">
                  <asp:ListItem Text="Sunday" Value="0"></asp:ListItem>
                  <asp:ListItem Text="Monday" Value="1"></asp:ListItem>
                  <asp:ListItem Text="Tuesday" Value="2"></asp:ListItem>
                  <asp:ListItem Text="Wednesday" Value="3"></asp:ListItem>
                  <asp:ListItem Text="Thursday" Value="4"></asp:ListItem>
                  <asp:ListItem Text="Friday" Value="5"></asp:ListItem>
                  <asp:ListItem Text="Saturday" Value="6"></asp:ListItem>
                </asp:DropDownList>
                    </asp:TableCell></asp:TableRow><asp:TableRow>
                    <asp:TableHeaderCell HorizontalAlign="Left">Holiday Date:</asp:TableHeaderCell><asp:TableCell>
                    <asp:TextBox runat="server" ID="addHolidayBox" AutoPostBack="true" /><asp:CalendarExtender runat="server" ID="addHoliday" Animated="true" TargetControlID="addHolidayBox" /></asp:TableCell></asp:TableRow><asp:TableRow>
                    <asp:TableHeaderCell HorizontalAlign="Left">Start Time:</asp:TableHeaderCell><asp:TableCell>

                        <asp:DropDownList ID="addStartTimeHour" runat="server"></asp:DropDownList>
                        <asp:DropDownList ID="addStartTimeMin" runat="server"></asp:DropDownList>
                        <asp:DropDownList ID="addStartTimeAmPm" runat="server">
                            <asp:ListItem>AM</asp:ListItem>
                            <asp:ListItem>PM</asp:ListItem>
                        </asp:DropDownList>

                    </asp:TableCell></asp:TableRow><asp:TableRow>
                    <asp:TableHeaderCell HorizontalAlign="Left">End Time:</asp:TableHeaderCell><asp:TableCell>

                    <asp:DropDownList ID="addEndTimeHour" runat="server"></asp:DropDownList>
                        <asp:DropDownList ID="addEndTimeMin" runat="server"></asp:DropDownList>
                        <asp:DropDownList ID="addEndTimeAmPm" runat="server">
                            <asp:ListItem>AM</asp:ListItem>
                            <asp:ListItem>PM</asp:ListItem>
                        </asp:DropDownList>

              </asp:TableCell></asp:TableRow><asp:TableRow>
              <asp:TableCell></asp:TableCell><asp:TableCell><asp:Button ID="btnAddHours" runat="server" Text="Add Hours" OnClick="btnAddHours_Click" /></asp:TableCell>  
      </asp:TableRow>

C#

        protected void btnAddHours_Click(object sender, EventArgs e)
    {
        hoursDataSource.InsertParameters["HolidayDate"].DefaultValue = addHoliday.SelectedDate.Value.ToString();
    }

You need to get the value from the Textbox instead CalendarExtender

It should be like...

hoursDataSource.InsertParameters["HolidayDate"].DefaultValue = addHolidayBox.Text;