flutter 输入框点击清除按钮背景变灰处理

报错：The following assertion was thrown while handling a gesture:

invalid text selection: TextSelection(baseOffset: 2, extentOffset: 2, affinity: TextAffinity.downstream, isDirectional: false)

 解决办法：

将searchController.clear(); 替换成如下

onCancel() {

    // 保证在组件build的第一帧时才去触发取消清空内容

    WidgetsBinding.instance.addPostFrameCallback((_) => searchController.clear.clear());

}