解决下拉树消失的问题

/*重写ComboBox中onViewClick方法，解决弹出的选择框中点击任何部分，包括选中节点、点击空白处以及点击展开下级节点，弹出框都会自动关闭问题*/
Ext.override(Ext.form.ComboBox, {?
?????? onViewClick : function(doFocus) {?
???????? var index = this.view.getSelectedIndexes()[0], s = this.store, r = s.getAt(index);?
???????? if (r) {?
????????? this.onSelect(r, index);?
???????? } else if (s.getCount() === 0) {?
?????????? this.collapse();?
???????? }?
???????? if (doFocus !== false) {?
?????????? this.el.focus();?
???????? }?
?????? }?
???? });