c# - Data source is an invalid type. It must be either an IListSource, IEnumerable, or IDataSource -

i trying fill 1 details view gridview selected index changing event,but got error,plz me

public void viewdetailsnew(decimal decdv)     {         subjectinfo infosubject = new subjectinfo();         subjectsp spcubject = new subjectsp();         dvsubject.datasource = spcubject.subjectviewdetails(decdv);         dvsubject.databind();         mvsubject.activeviewindex = 1;     }  public subjectinfo subjectviewdetails(decimal decsubjectid)     {         subjectinfo infosubject = new subjectinfo();         sqldatareader sqlreader = null;         try         {             if (sqlcon.state == connectionstate.closed)             {                 sqlcon.open();             }             sqlcommand sqlcmd = new sqlcommand("subjectview", sqlcon);             sqlcmd.commandtype = commandtype.storedprocedure;             sqlcmd.parameters.add("@subjectid", sqldbtype.decimal).value = decsubjectid;             sqlreader = sqlcmd.executereader();             while (sqlreader.read())             {                 infosubject.subjectid = decimal.parse(sqlreader["subjectid"].tostring());                 infosubject.subjectname = sqlreader["subjectname"].tostring();                 infosubject.shortname = sqlreader["shortname"].tostring();              }         }         catch         {             throw;         }                 {             sqlreader.close();             sqlcon.close();         }          return infosubject;     }  protected void gvviewsubject_selectedindexchanging(object sender, gridviewselecteventargs e)     {         viewstate["subjectid"] = gvviewsubject.datakeys[e.newselectedindex]["subjectid"].tostring();         decimal decdv = decimal.parse(viewstate["subjectid"].tostring());         viewdetailsnew(decdv);     } 

you trying bind single object when need collection or ienumerable

try this

 public ienumerable<subjectinfo> subjectviewdetails(decimal decsubjectid) {     var list = new list<subjectinfo>();      try     {         if (sqlcon.state == connectionstate.closed)         {             sqlcon.open();         }         sqlcommand sqlcmd = new sqlcommand("subjectview", sqlcon);         sqlcmd.commandtype = commandtype.storedprocedure;         sqlcmd.parameters.add("@subjectid", sqldbtype.decimal).value = decsubjectid;         using (var sqlreader = sqlcmd.executereader())         {             while (sqlreader.read())             {                 subjectinfo infosubject = new subjectinfo();                 infosubject.subjectid = decimal.parse(sqlreader["subjectid"].tostring());                 infosubject.subjectname = sqlreader["subjectname"].tostring();                 infosubject.shortname = sqlreader["shortname"].tostring();                 list.add(infosubject);             }         }     }     catch     {         throw;     }         {         sqlcon.close();     }      return list; }