Grid导出页面数据时，点击导出的图标显示不出来选项列表

今天下午开始摸索使用grid扩展来展示表格，现在已经能展示出数据来了，但是点击导出的图标却显示不出来选项列表。
现在页面效果如下：

view部分的代码如下：

<code>'pjax' => true,//加载loading动画
'bordered' => true,
'striped' => false,
'condensed' => false,
'responsive' => true,
'hover' => true,
'floatHeader' => true,
'floatHeaderOptions' => ['scrollingTop' => 50],
// 'showPageSummary' => true,
'panel' => [
    'heading'=>'<h3 class="panel-title">
<i class="glyphicon glyphicon-globe"></i> Countries</h3>',
     'type'=>'success',
     'before'=>Html::a('<i class="glyphicon glyphicon-plus"></i> Create Country', ['create'], ['class' => 'btn btn-success']),
     'after'=>Html::a('<i class="glyphicon glyphicon-repeat"></i> Reset Grid', ['get-school-in-province'], ['class' => 'btn btn-info']),
     'footer'=>false,
     'export'=>true,
     'toolbar'=>true,
],
        
'exportConfig' => [
     GridView::PDF => [
         'label' => '导出CSV',
         'iconOptions' => ['class' => 'text-primary'],
         'showHeader' => true,
         'showPageSummary' => true,
         'showFooter' => true,
         'showCaption' => true,
         'filename' => '用户表'.date("Y-m-d"),
         'alertMsg' => '确定要导出CSV格式文件？',
         'options' => [
              'title'=>'',
          ],
          'mime' => 'application/pdf',
          'config' => [
                'colDelimiter' => ",",
                'rowDelimiter' => "\r\n",
          ],
     ],
            // GridView::HTML => [],
            // GridView::PDF => [],</code>

]

报错如下：

为什么点击右上角的导出下拉框，却没反应呢。
求答疑解惑！！！

回复内容：

今天下午开始摸索使用grid扩展来展示表格，现在已经能展示出数据来了，但是点击导出的图标却显示不出来选项列表。
现在页面效果如下：

view部分的代码如下：

<code>'pjax' => true,//加载loading动画
'bordered' => true,
'striped' => false,
'condensed' => false,
'responsive' => true,
'hover' => true,
'floatHeader' => true,
'floatHeaderOptions' => ['scrollingTop' => 50],
// 'showPageSummary' => true,
'panel' => [
    'heading'=>'<h3 class="panel-title">
<i class="glyphicon glyphicon-globe"></i> Countries</h3>',
     'type'=>'success',
     'before'=>Html::a('<i class="glyphicon glyphicon-plus"></i> Create Country', ['create'], ['class' => 'btn btn-success']),
     'after'=>Html::a('<i class="glyphicon glyphicon-repeat"></i> Reset Grid', ['get-school-in-province'], ['class' => 'btn btn-info']),
     'footer'=>false,
     'export'=>true,
     'toolbar'=>true,
],
        
'exportConfig' => [
     GridView::PDF => [
         'label' => '导出CSV',
         'iconOptions' => ['class' => 'text-primary'],
         'showHeader' => true,
         'showPageSummary' => true,
         'showFooter' => true,
         'showCaption' => true,
         'filename' => '用户表'.date("Y-m-d"),
         'alertMsg' => '确定要导出CSV格式文件？',
         'options' => [
              'title'=>'',
          ],
          'mime' => 'application/pdf',
          'config' => [
                'colDelimiter' => ",",
                'rowDelimiter' => "\r\n",
          ],
     ],
            // GridView::HTML => [],
            // GridView::PDF => [],</code>

]

报错如下：

为什么点击右上角的导出下拉框，却没反应呢。
求答疑解惑！！！

有没有大神了解这个，求指教