asp.net - How to generate a print preview in a single button click in report viewer? -

this aspx page..................

    <asp:panel id="updatepanel1" runat="server" visible="false" >               <rsweb:reportviewer id="reportingforprintingreportviewer" runat="server"            width="100%" height="100%" font-names="verdana" font-size="8pt"            interactivedeviceinfos="(collection)" waitmessagefont-names="verdana"            waitmessagefont-size="14pt">              <localreport reportpath="report.rdlc">            <datasources>            <rsweb:reportdatasource datasourceid="objectdatasource2" name="dataset1" />            </datasources>            </localreport>            </rsweb:reportviewer>              <asp:objectdatasource id="objectdatasource2" runat="server"               selectmethod="getdata" typename="dataset1tableadapters.tbltotalfeetableadapter">            </asp:objectdatasource>                  </asp:panel> <asp:button id="btnsubmit" runat="server" text="submit" width="150px"            onclick="btnsubmit_click" />        <asp:button id="btnreset" runat="server" text="reset" width="150px" />        <asp:button id="btncreatebill" runat="server" text="createbill" width="150px"             onclick="btncreatebill_click"/>          <asp:popupcontrolextender id="btncreatebill_popupcontrolextender" offsetx="-1100" offsety="115"             runat="server" dynamicservicepath="" enabled="true" extendercontrolid=""             targetcontrolid="btncreatebill" popupcontrolid="updatepanel1">        </asp:popupcontrolextender> 

this cs page

 protected void btncreatebill_click(object sender, eventargs e)     {         displayreport();         updatepanel1.visible = true;      }     private datatable totalinfodata()     {         try         {             //dataclassesdatacontext db = null;             //db = new dataclassesdatacontext();             //var s = p in db.tbltotalfeess             //        p.class == classdropdownlist.selecteditem.value && p.studentid == convert.toint32(studentnamedropdownlist.selectedvalue)             //        select p;              //datatable dt = new datatable();             //sqlhelper sqhlpr = new sqlhelper();             //sqhlpr.sqltext = "select * tbltotalfee class='" + classdropdownlist.selecteditem.value + "'" + "and studentid='" + studentnamedropdownlist.selectedvalue + "'";             //datatable dt = sqhlpr.getdatatable(false);             //return dt;             try             {                 // open sql connection                   sqlconnection sqlcon = new sqlconnection(@"data source=pratikpc;initial catalog=dbbilling2.0;integrated security=true");                 sqlcon.open();                  // create command                   sqlcommand sqlcomm = new sqlcommand();                 sqlcomm.connection = sqlcon;                 sqlcomm.commandtype = commandtype.text;                 sqlcomm.commandtext = "select * tbltotalfee class='" + classdropdownlist.selecteditem.value + "'" + "and studentid='" + studentnamedropdownlist.selectedvalue + "'";                  // create instance of northwind datasetxsd                   dataset1.tbltotalfeedatatable dtbl = new dataset1.tbltotalfeedatatable();                  // set data commands                   sqldataadapter sqlda = new sqldataadapter(sqlcomm);                 sqlda.fill(dtbl); // fill data in northwinddataset object.                    return dtbl;              }             catch (exception ex)             {                 throw new exception(ex.message);             }            }           catch (exception ex)         {             throw new exception(ex.message);         }     }     private void displayreport()     {         try         {             // clear data source                reportingforprintingreportviewer.localreport.datasources.clear();              // set datasource report                // first parameter - report dataset name               // second parameter - datasource object i.e datatable               reportingforprintingreportviewer.localreport.datasources.add(new reportdatasource("dataset1", totalinfodata()));              // or set report path               reportingforprintingreportviewer.localreport.reportpath = httpcontext.current.server.mappath("~/report.rdlc");              // refresh , display report               reportingforprintingreportviewer.localreport.refresh();          }         catch (exception ex)         {             throw new exception(ex.message);         }     } 

i have click btncreatebill twice generate report viewer. why?? , how can generate report viewer in single click of button??it's urgent can suggest me anything.

are call data method(your data source load method ) in inside of !ispostback ?

for this

protected void page_load(object sender, eventargs e) {         if (!page.ispostback)         {                 getdata()// data source load method         } }