Yii Class CActiveDataProvider not found

I'm new to Yii, and I'm getting this error "Class 'app\controllers\CActiveDataProvider' not found" while running a widget.

This is my code:

models/industrial.php:

<?php

namespace app\models;

use yii\db\ActiveRecord;

class Industrial extends ActiveRecord
{
}

controllers/IndustrialController.php:

<?php

namespace app\controllers;

use yii\web\Controller;
use yii\data\Pagination;
use app\models\industrial;


class IndustrialController extends Controller
{


    public function actionIndex()
    {
        $dataProvider=new CActiveDataProvider('Industrial', array(

    'pagination'=>array(
        'pageSize'=>20,
    ),
));
        $query = industrial::find();

        $pagination = new Pagination([
            'defaultPageSize' => 20,
            'totalCount' => $query->count(),
        ]);

        $industrials = $query->orderBy('Company_Name')
            ->offset($pagination->offset)
            ->limit($pagination->limit)
            ->all();




        return $this->render('index', [
            'industrials' => $industrials,
            'pagination' => $pagination,
            'dataProvider'=>$dataProvider,
        ]);



}
}

views/industrial/index.php:

<?php
use yii\helpers\Html;
use yii\widgets\LinkPager;
?>
<h1>Industrial Companies</h1>
<ul>
<?php

use kartik\export\ExportMenu;

use kartik\grid\GridView;

$gridColumns = [
    ['class' => 'yii\grid\SerialColumn'],
    'id',
    'name',
    [
        'attribute'=>'Name',
        'label'=>'Name',
        'vAlign'=>'middle',
        'width'=>'190px',
        'value'=>function ($model, $key, $index, $widget) { 
            return Html::a($model->Name, '#', []);
        },
        'format'=>'raw'
    ],
    'Name',
    'Location',
    'Telephone',

];
echo ExportMenu::widget([
    'dataProvider' => $dataProvider,
    'columns' => $gridColumns,
    'fontAwesome' => true,
    'dropdownOptions' => [
        'label' => 'Export All',
        'class' => 'btn btn-default'
    ]
]) . "<hr>\n".
GridView::widget([
    'dataProvider' => $dataProvider,
    'columns' => $gridColumns,
    'export' => [
        'fontAwesome' => true,
    ]
]);



$array = (array) $industrials;



function build_table($array){

    // start table

    $html = '<table class="altrowstable" id="alternatecolor">';

    // header row

    $html .= '<tr>';

    foreach($array[0] as $key=>$value){

            $html .= '<th>' . $key . '</th>';

        }

    $html .= '</tr>';

    // data rows

    foreach( $array as $key=>$value){

        $html .= '<tr>';

        foreach($value as $key2=>$value2){

            $html .= '<td>' . $value2 . '</td>';

        }

        $html .= '</tr>';

    }

    // finish table and return it

    $html .= '</table>';

    return $html;

}



echo build_table($array);

?>


<?= LinkPager::widget(['pagination' => $pagination]) ?>

What is the problem here? Could you please help me?

I believe your issue is caused by your use of namespaces, which Yii 1.1 does not use. Because you declared the namespace to be app/controllers, the CActiveDataProvider is looked for within that namespace, instead of in the global namespace; specifically, it is looking for the class file in the app/controllers directory.

To resolve this, try referencing the class as \CActiveDataProvider to cause it to look for the class using Yii's autoloader.