原因分析如下:
1:
If you set the <code>dataProvider</code> property and then immediately call
the <code>expandChildrenOf()</code> method, you may not see the correct behavior.
You should either wait for the component to validate,
or call the <code>validateNow()</code> method before calling <code>expandChildrenOf()</code>.</p>
2:調用 expandItem 展開 子條目 ,判斷 父條目是否已經展開。