extjs3 RadioGroup单选变多选问题

这个问题在网上搜了好久才找到解决办法，其实很简单，关键位置就是radio 的name问题

<span style="white-space:pre">		</span>{
	    	            xtype: 'radiogroup',
	    	            width: 500,
	    	            fieldLabel: '',
	    	            allowBlank: false,
	    	            name:'file_type',
	    	            cls: 'x-check-group-alt',
	    	            items: [
	    	                {name:'file_type',boxLabel: '全部',id:'radio_all',inputValue:'all' , checked:true},
	    	                {name:'file_type',boxLabel: 'PDF',id:'radio_pdf',inputValue:'pdf'},
	    	                {name:'file_type',boxLabel: 'txt',id:'radio_txt',inputValue:'txt'},
	    	                {name:'file_type',boxLabel: 'xml',id:'radio_xml',inputValue:'xml'},
	    	                {name:'file_type',boxLabel: 'doc',id:'radio_doc',inputValue:'doc'}]
	    	        }