设置combobox下拉框不能选择

<link rel="stylesheet" type="text/css" href="../ext-4.2.1.883/resources/css/ext-all-neptune.css"/>

<script type="text/javascript" src="../ext-4.2.1.883/ext-all.js"></script>

<script type="text/javascript" src="../ext-4.2.1.883/ext-theme-neptune.js"></script>

<script type="text/javascript">

Ext.onReady(function(){

var states = Ext.create('Ext.data.Store', {

fields: ['abbr', 'name'],

data : [

{"abbr":"AL", "name":"Alabama"},

{"abbr":"AK", "name":"Alaska"},

{"abbr":"AZ", "name":"Arizona"}

//...

]

});

// Create the combo box, attached to the states data store

var combo = Ext.create('Ext.form.ComboBox', {

fieldLabel: 'Choose State',

store: states,

displayField: 'name',

valueField: 'abbr',

renderTo: Ext.getBody(),

forceSelection:false,

value:'AK',

listeners:{

beforedeselect:function(combo, record, index, eOpts){ //在此事件下return false;设置combobox下拉框不能选择

return false;

}

}

});

});

</script>