Extjs4.2 多选下拉框

//多选下拉框
Ext.define('MDM.view.custom.MultiComboBox', {
    extend: 'Ext.form.ComboBox',
    alias: 'widget.multicombobox',
    xtype: 'multicombobox',
    initComponent: function() {
        this.multiSelect = true;
        this.listConfig = {
            itemTpl: Ext.create('Ext.XTemplate',
'<input type=checkbox>{' + this.displayField + '}'),
            onItemSelect: function(record) {
                var node = this.getNode(record);
                var count = this.getStore().data.length;
                if (node) {
                    Ext.fly(node).addCls(this.selectedItemCls);
                    var checkboxs = node.getElementsByTagName("input");
                    if (checkboxs != null) {
                        var checkbox = checkboxs[0];
                        checkbox.checked = true;
                    }
                }
            },
            onItemDeselect: function(record) {
            var node = this.getNode(record);
            var count = this.getStore().data.length;
            if (node) {
                Ext.fly(node).removeCls(this.selectedItemCls);
                var checkboxs = node.getElementsByTagName("input");
                if (checkboxs != null) {
                    var checkbox = checkboxs[0];
                    checkbox.checked = false;
                }
            }
            },
            listeners: {
                itemclick: function(view, record, item, index, e, eOpts) {
                    var isSelected = view.isSelected(item);
                    var checkboxs = item.getElementsByTagName("input");
                    if (checkboxs != null) {
                        var checkbox = checkboxs[0];
                        if (!isSelected) {
                            checkbox.checked = true;
                        } else {
                            checkbox.checked = false;
                        }
                    }
                }
            }
        }
        this.callParent();
    }
});