Dojox DataGrid: achieve row selection only by Checkboxes

http://stackoverflow.com/questions/10914157/dojox-datagrid-achieve-row-selection-only-by-checkboxes

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.7.1/dijit/themes/claro/claro.css">
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.7.2/dojox/grid/resources/claroGrid.css">
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.7.2/dojox/grid/resources/Grid.css">
<button onclick="showSelect()">
Show
</button>
<div id="gridDiv"></div>

CSS

#grid {
  width: 43em;
  height: 20em;
}

JavaScript

dojo.require("dojox.grid.DataGrid");
dojo.require("dojo.data.ItemFileWriteStore");
dojo.require("dojox.grid._CheckBoxSelector");
dojo.require("dojo.store.Memory");
dojo.require("dojo.data.ObjectStore");

dojo.ready(function(){

	var fruit = ['apple', 'orange', 'banana'];
	fruit.splice(0,1);
  alert(fruit);


		// Create statistic data grid
				var data = {
						identifier: 'id',
						items: []
						    
				};
				
				for (var i=0; i<10; i++){
					var tmp_data = {
							'principalNo': 1, 
							'principalName': 2,
				        	'systemCriteria': 3,
				        	'userCriteria': 4,
				        	'selected': 5,
				        	'pendingCheck': 6,
				        	'checked': 7,
				        	'furtherReview': 8,
				        	'notSelected': 9,
				        	'total': 10			        	
					};
					data.items.push(tmp_data);
				}
				
			
				
				var objectStore = new dojo.store.Memory({data:data});
				var sampleStore = new dojo.data.ObjectStore({objectStore: objectStore});		
				var cellslayout = [[
							{'name': 'Ref No', 'field': 'principalNo', 'width': '5%'},
							{'name': 'Principal Name', 'field': 'principalName', 'width': '20%'},
			                {'name': 'System Criteria', 'field': 'systemCriteria', 'width': '5%'},			        
			                {'name': 'User Criteria', 'field': 'userCriteria' , 'width': '10%'},
			                {'name': 'Selected', 'field': 'selected', 'width': '5%'},
			                {'name': 'Pending Check', 'field': 'pendingCheck', 'width': '10%'},
			                {'name': 'Checked', 'field': 'checked', 'width': '5%'},
			                {'name': 'Further Review', 'field': 'furtherReview', 'width': '10%'},
			                {'name': 'Not selected', 'field': 'notSelected', 'width': '10%'},
			                {'name': 'Total', 'field': 'total', 'width': '10%'}
				          ]];
				var gridLayout = [ 
					cellslayout
				];
				
				this.sampleStatisticGrid = new dojox.grid.DataGrid({
			        id: 'statisticGrid',
							store:...