c# - Dependent DropDownList in FormView -


i trying create 2 drop down lists in form view values displayed in second drop down dependent upon first drop down.the first list contains class numbers contained in sql table "classes" , second drop down list contains class sections in same sql table "classes". want able select class number , have sections correspond class number pop up.

example classes table:

number:   section:   sln:   210       1          a-1   210       2          a-2   210       3          a-3   340       1          b-1   340       7          b-7  

i have first list number set using

   <asp:dropdownlist id="ddlnumber" runat="server"      datasourceid="sqldsclasses"      autopostback="true" datatextfield="number" datavaluefield="number">     </asp:dropdownlist>  drop down ,  <asp:sqldatasource id="sqldsclasses" runat="server"        connectionstring="<%$ connectionstrings:reinstatementcs %>"  selectcommand="select [prefix], [number], [location], [sln],                               [starttime], [endtime], [classday], [classcredit], [classsection] [classes]">    </asp:sqldatasource> corresponding sqldatasource 

so far have tried use

select [classsection] [classes] [number] = numberdropdownlist.datavaluefield section list:  <asp:dropdownlist id="classsectiondropdownlist" runat="server" datasourceid="sqldsnumsec"                                              datatextfield="classsection" datavaluefield="classsection"  autopostback="true">                                         </asp:dropdownlist> 

the form view being used set follows:

<asp:formview id="fvstudentclass" runat="server" datasourceid="sqldsstudentclass"                         datasourceid2="sqldsaccess" emptydatatext="student class not completed">                         <edititemtemplate>                             <table style="width:100%;">                                 <tr>                                     <td>                                         prefix:                                     </td>                                     <td>                                         ucoll</td>                                     <td>                                         number:                                     </td>                                     <td>                                         <asp:dropdownlist id="ddlnumber" runat="server" datasourceid="sqldsclasses"  autopostback="true"                                             datatextfield="number" datavaluefield="number">                                         </asp:dropdownlist>                                     </td>                                      <td>                                          section:                                     </td>                                     <td>                                         <asp:dropdownlist id="sectiondropdownlist" runat="server" datasourceid="sqldsnumsec"                                              datatextfield="section" datavaluefield="section"  autopostback="true">                                         </asp:dropdownlist>                                     </td>                                 </tr>                             </table>                             <asp:linkbutton id="updatebutton" runat="server" causesvalidation="true" commandname="update"                                 text="update" />                             &nbsp;<asp:linkbutton id="updatecancelbutton" runat="server" causesvalidation="false"                                 commandname="cancel" text="cancel" />                         </edititemtemplate>                         <insertitemtemplate>                             istransfer:                             <asp:checkbox id="istransfercheckbox" runat="server"                                  checked='<%# bind("istransfer") %>' />                             <br />                             prefix:                             <asp:textbox id="prefixtextbox" runat="server" text='<%# bind("prefix") %>' />                             <br />                             number:                             <asp:textbox id="numbertextbox" runat="server" text='<%# bind("number") %>' />                             <br />                             section:                             <asp:textbox id="sectiontextbox" runat="server"                                  text='<%# bind("section") %>' />                             <br />                             id:                             <asp:textbox id="idtextbox" runat="server" text='<%# bind("id") %>' />                             <br />                             <asp:linkbutton id="insertbutton" runat="server" causesvalidation="true" commandname="insert"                                 text="insert" />                             &nbsp;<asp:linkbutton id="insertcancelbutton" runat="server" causesvalidation="false"                                 commandname="cancel" text="cancel" />                         </insertitemtemplate>                         <itemtemplate>                             <table style="width:100%;">                                 <tr>                                     <td>                                         prefix:</td>                                     <td>                                         <asp:label id="prefixlabel" runat="server" text='<%# bind("prefix") %>' />                                     </td>                                     <td>                                         number:</td>                                     <td>                                         <asp:label id="numberlabel" runat="server" text='<%# bind("number") %>' />                                     </td>                                     <td>                                         classsection:</td>                                     <td>                                         <asp:label id="classsectionlabel" runat="server"                                              text='<%# bind("classsection") %>' />                                     </td>                                 </tr>                                 <tr>                                     <td>                                         istransfer:</td>                                     <td>                                         <asp:checkbox id="istransfercheckbox" runat="server"                                              checked='<%# bind("istransfer") %>' enabled="false" />                                     </td>                                 </tr>                             </table>                             <asp:linkbutton id="editbutton" runat="server" causesvalidation="false" commandname="edit"                                 text="edit" />                         </itemtemplate>                     </asp:formview> 

with sqldatasource:

<asp:sqldatasource id="sqldsstudentclass" runat="server" connectionstring="<%$ connectionstrings:reinstatementcs %>"                          deletecommand="delete [studentclass] [sln] = @sln"                          insertcommand="insert [studentclass] ([sln],[id]) values (@sln, @id)"                         selectcommand="select distinct classes.number, classes.section, studentclass.id      studentclass      left join accesslist on accesslist.alid = studentclass.id     join classes on studentclass.sln = classes.sln ([sln] = @sln)"      <!--accesslist gives information user-->                                             updatecommand="update [studentclass] set [sln] = @sln, [id] = @id [sln] = @sln">                          <deleteparameters>                             <asp:parameter name="sln" type="int32" />                         </deleteparameters>                         <insertparameters>                             <asp:parameter name="sln" type="string" />                             <asp:parameter name="id" type="string" />                         </insertparameters>                         <selectparameters>                             <asp:querystringparameter name="id" querystringfield="alid"                                  type="string" />                         </selectparameters>                         <updateparameters>                             <asp:parameter name="id" type="string" />                             <asp:parameter name="sln" type="int32" />                         </updateparameters>                     </asp:sqldatasource> 

example of form in action using example tables above:

number drop down: 210                ->   select 210      340    section drop down: 1 2                  -> select 3 3 

take @ article:

http://csharpdotnetfreak.blogspot.com/2009/03/populate-dropdown-based-selection-other.html

it explains how achive want.

also, alternative, may use ajax: http://www.asp.net/ajaxlibrary/ajaxcontroltoolkitsamplesite/cascadingdropdown/cascadingdropdown.aspx


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