Mvvm Light Dispatcher Helper -

how can use dispatcher helper progress bar in mvvm-light. i'm accessing ui element defined in viewmodel , think dispatcherhelper solved this, seems progressbar not updated when ran backgroundworker dispatcherhelper. please help:

here's code :

        _worker = new backgroundworker() {             workerreportsprogress = true,             workersupportscancellation = true         };           _grid = new grid();         _worker.dowork += (sender,e) => dispatcherhelper.uidispatcher.invoke(() => {             try{                 var vworker = (backgroundworker) sender;                  reportcolumns = new list<reportcolumn>();                 #region set report item column                 for(var = 1;i <= _reportbal.reportitemcontent.columns.count - 1;i++) {                     var vcolumnsitems = reportparser.parsecolumnattributes(_reportbal.reportitemcontent.columns[i].columnname);                     var vcolumn = new reportcolumn();                     vcolumn.datatype = vcolumnsitems[0];                     vcolumn.width = vcolumnsitems[1];                     vcolumn.header = vcolumnsitems[2];                     vcolumn.datafield = vcolumnsitems[2];                     reportcolumns.add(vcolumn);                 }                  if(reportcolumns != null) {                     for(int ctrcol = 0;ctrcol <= reportcolumns.count - 1;ctrcol++) {                         var sp = new stackpanel { orientation = orientation.horizontal };                         _grid.columndefinitions.add(new columndefinition {                             width =                                 new gridlength(convert.todouble(reportcolumns[ctrcol].width))                         });                         var tb = new textblock {                             text = reportcolumns[ctrcol].datafield,                             fontweight = fontweights.demibold,                             margin = new thickness(8,0,8,0),                             textwrapping = textwrapping.wrap                         };                         sp.children.add(tb);                         grid.setrow(sp,0);                         grid.setcolumn(sp,ctrcol);                         _grid.children.add(sp);                     }                 }                  #endregion                  #region set report item row                 gridhelper.setrowcount(_grid,_reportbal.reportitemcontent.rows.count + 1);                 for(int rrow = 0;rrow <= _reportbal.reportitemcontent.rows.count - 1;rrow++) {                      if(vworker.cancellationpending) {                         e.cancel = true;                         break;                     }                      for(int ccol = 0;ccol <= reportcolumns.count - 1;ccol++) {                          string vvalue = _reportbal.reportitemcontent.rows[rrow][ccol + 1].tostring(); ;                          var sp = new stackpanel { orientation = orientation.horizontal };                          var tb = new textblock {                             text = vvalue,                             width = double.parse(reportcolumns[ccol].width),                             margin = new thickness(8,3,8,3),                             textwrapping = textwrapping.wrap                         };                          sp.children.add(tb);                          grid.setcolumn(sp,ccol);                         grid.setrow(sp,rrow + 1);                         _grid.children.add(sp);                       }                      if(vworker.workerreportsprogress) {                         _recordcount = _reportbal.reportitemcontent.rows.count;                         int vpercentcomplete = (int)((float)rrow / (float)_recordcount * 100);                         string updatemessage =                             string.format("record(s) {0} of {1}",rrow,_recordcount);                         vworker.reportprogress(vpercentcomplete,updatemessage);                     }                 }                  #endregion                  e.result = _grid;                 //_reportitemcontent = _grid;             }             catch(exception exception) {                 throw new exception("#error: error parsing report items" + environment.newline +                     environment.newline + "#internal error: " + exception.message,exception);              }         });         _worker.progresschanged += (s,e) => dispatcherhelper.runasync((() =>{             progresspercentage = e.progresspercentage;             output = (string)e.userstate;         }));          _worker.runworkercompleted += (s,e) => /*dispatcherhelper.uidispatcher.invoke((() =>*/ {             if(e.error != null) throw new exception("error tae");             _reportitemcontent = (grid)e.result;         };