Set Start Date And EndDate of AjaxCalendarExtendar based on dropdownlist Selected Value in ASP.Net

Hi Amol111,

I have created sample that full fill your requirement.

HTML

<div>
    <cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </cc1:ToolkitScriptManager>
    <table>
        <tr>
            <td>
                <asp:DropDownList runat="server" ID="ddlYears" AutoPostBack="true" OnSelectedIndexChanged="SelectionChanged">
                    <asp:ListItem Text="Select" />
                    <asp:ListItem Text="2015" />
                    <asp:ListItem Text="2016" />
                </asp:DropDownList>
            </td>
            <td>
                <asp:TextBox ID="txtDate" runat="server" ReadOnly="true"></asp:TextBox>
                <asp:ImageButton ID="imgPopup" ImageUrl="images/calendar.png" ImageAlign="Bottom"
                    runat="server" />
                <cc1:CalendarExtender ID="ce1" PopupButtonID="imgPopup" runat="server" TargetControlID="txtDate"
                    Format="dd/MM/yyyy">
                </cc1:CalendarExtender>
            </td>
        </tr>
    </table>
</div>

Code

protected void SelectionChanged(object sender, EventArgs e)
{
    int selected = Convert.ToInt32(ddlYears.SelectedItem.Text);
    DateTime startDate = new DateTime(selected, 04, 01);
    DateTime endDate = new DateTime(selected + 1, 03, 31);
    ce1.StartDate = startDate;
    ce1.EndDate = endDate;
}

Screenshot