Oct 9, 2015

Dropdownlist selectedindexchanged event is not firing

<asp:DropDownList ID="ddlSource" runat="server" DataSourceID="SqlDataSource1" DataTextField="vcSuplierNm" ViewStateMode="Enabled DataValueField="vcSuplierCode" EnableViewState="true" AppendDataBoundItems="true" OnSelectedIndexChanged="ddl_OnSelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>

Add property ViewStateMode="Enabled" and EnableViewState="true"
in drop DropDownList