jqGrid reload grid

It's an addition for previous my question about adding columns into jqGrid-based table. Here my new js-code:

var col_names = ['First', 'Second', 'Third', 'Fourth', 'Fifth'];
var col_model = [
      {name:'invid', index:'invid', width:100}, 
      {name:'invdate', index:'invdate', width:90}, 
      {name:'amount', index:'amount', width:80, align:'right'}, 
      {name:'tax', index:'tax', width:开发者_运维问答80, align:'right'}, 
      {name:'total', index:'total', width:80, align:'right'}, 
];

function createGrid()
{
  var handle = $("#list").jqGrid({
    url:'data.xml',
    datatype: 'xml',
    mtype: 'GET',
    colNames: col_names,
    colModel : col_model,
  }); 
}

Now I call createGrid(); after document is loaded, everything works fine. Now I want to add a new column (with empty data) and reload jqGrid:

  $("#add_column").click(function() {
        $('#list').trigger("DestroyGrid"); // Also tried UnloadGrid

        col_names.push('New');
        col_model.push({name: 'test', index: 'test', width: 100});

        createGrid(); // And recreate grid
  });

But nothing happens, why?

UPD

  $("#add_column").click(function() {
        col_names.push('New');
        col_model.push({name: 'test', index: 'test', width: 100});

        $('#list').trigger("reloadGrid");
  });

The same situation

UPD2 I tried these:

ajaxGridOptions: {cache: false},
loadonce:false

Didn't change the situation.

You can do about following

var counter=1; // to be able to click more then one time
$("#add_column").click(function() {
    $("#list").jqGrid('GridUnload');

    col_names.push('New'+counter);
    col_model.push({name: 'test'+counter, index: 'test'+counter, width: 100});
    counter++;

    createGrid();
});

try not to Destroy/Create, but .trigger("reloadGrid");

UPD:: try to pass loadonce:false to grid creation params

UPD2:: Seemed like jQgrid cant operate with column changes "On fly". Try to destroy first grid and create another one instead of it.