但是我无法在文档中找到或遗漏它,我如何在页脚中显示列的总和.

这是我在index.PHP中的完整代码

<?PHP 
        $gridColumns = [
    ['class' => 'yii\grid\SerialColumn'],'id',[
        //'attribute'=>'service_name','attribute'=>'service_name','value'=>'serviceName.services',],[
        'attribute'=>'room_category','value'=>'roomCategory.room_category'
     ],'charges_cash','charges_cashless',['class' => 'yii\grid\ActionColumn']
];

    echo ExportMenu::widget([
    'dataProvider' => $dataProvider,'columns' => $gridColumns,'fontAwesome' => true,'showPageSummary' => true,'dropdownOptions' => [
        'label' => 'Export All','class' => 'btn btn-default'
    ]
]) 
        ?>
    </div></div>


    <?= GridView::widget([
        'dataProvider' => $dataProvider,'filterModel' => $searchModel,'columns' => [
            ['class' => 'yii\grid\SerialColumn'],//'service_name',[
                //'attribute'=>'service_name',// 'room_category',[
                'attribute'=>'room_category','value'=>'roomCategory.room_category'
            ],['class' => 'yii\grid\ActionColumn'],'showFooter' => true
    ]); ?>

</div>

寻求这方面的一些帮助.
谢谢.