Extjs4:给Grid的Column加上提示

{
                    xtype: 'gridcolumn',
                    sortable: false,
                    dataIndex: 'company',
                    flex: 1,
                    text: '公司',
                    tooltip: '公司名称',
                    renderer: function(value, metaData, data) {
                    	var cname = value;
                    	if(value.length>10){
                    		 metaData.tdAttr = 'data-qtip="'+value+'"';
                    		cname = value.substring(0,10)+"...";
                    	}
                        return cname;
                    },
                }