c# - asp.net gridview set null to datasource -

asp.net html:

<asp:gridview id="grddynamic" runat="server"      allowpaging="true"      gridlines="none"      pagesize="20"      cellspacing="0"      alternatingitemstyle-cssclass="rowb renklisatir"      cssclass="tumislerimtable"      allowsorting="true"     autogeneratecolumns="false">     <headerstyle cssclass="rowa" /> </asp:gridview>  <asp:imagebutton id="search" runat="server"      alternatetext="search"      imageurl="../images/search.gif"      onclick="search_click"> </asp:imagebutton> 

if click search button below method works

search_click method

protected void search_click(object sender, imageclickeventargs e) {     datatable nulldatatable = new datatable();     nulldatatable = null;     grddynamic.datasource = nulldatatable; // i'm trying clear gridview datasource not working me     grddynamic.databind();      //after bind datasource below programatically      datatable dt = new datatable();     datarow drow = dt.newrow();      foreach (var project in multicombobox.checkeditems.tolist())     {         dataset ds = procedure.getprojectbyid(type.selectedvalue, startdate, enddate);          if (ds.tables[0].rows.count > 0)         {             datacolumn dcol = new datacolumn(ds.tables[0].rows[0 ["flow_name"].tostring(), typeof(system.int32));             dt.columns.add(dcol);              drow[ds.tables[0].rows[0]["flow_name"].tostring()] = ds.tables[0].rows[0]["sayi"].tostring();         }     }      dt.rows.add(drow);      foreach (datacolumn col in dt.columns)     {         boundfield bfield = new boundfield();         bfield.datafield = col.columnname;         bfield.headertext = col.columnname;         grddynamic.columns.add(bfield);     }      grddynamic.datasource = dt;     grddynamic.databind(); } 

if click search button first time result below

flow_name  1 

if click search button second time result below

flow name  flow_name    1           1 

if click search button third time result below

flow name  flow_name   flow_name   1           1           1 

question:

when click button column , row copies 1 more set datasource null onclick search button not working.how can solve problem how can prevent copy same column , row values ?

note data binding trick clearing rows, not columns. , rows not matter because 1 more data bind in end of click handler, fills gridview data anew.

as columns, run every button click

foreach (datacolumn col in dt.columns) 

effectively adding new columns every time. should run once, , on subsequent clicks make sure not add added columns. or better yet try define list of columns declaratively in markup , rid of column-adding code @ all.