How to access variable from other view page on yii2? - yii2

Question

How to access variable ($imodel->grade) in tampil.php page and then subsequently put on the page view.php with post method. Sorry for the question, i'm newbie in OOP, MVC and Yii. Please help me guys
Here is The code of actionIndex:
public function actionIndex()
{
$imodel = new Grade();
if($imodel->load(Yii::$app->request->post()))
{
$imodel->load(Yii::$app->request->post());
$imodel->grade;
$query = Nilaiharian::find(); //select nis, $grade, nama from nilaiharian
$dataProvider = new ActiveDataProvider(['query' => $query,]);
return $this->render('tampil', ['imodel' => $imodel, 'dataProvider' => $dataProvider,] );
}
else
{
return $this->render('index', ['imodel' => $imodel, ] );
}
}
And this is a code of tampil.php
<?php
echo "Nilai untuk ".$imodel->grade;
echo "<br>";
echo GridView::widget([
'dataProvider' => $dataProvider,
'columns' => [
['class' => 'yii\grid\SerialColumn'],
'nis',
$imodel->grade,
'nama',
['class' => 'yii\grid\ActionColumn',
'template' => '{view}{update}{delete}',
'buttons' => [
'view' => function ($url, $model) {
return Html::a('<i class="glyphicon glyphicon-eye-open"></i>',
$url, ['title' => Yii::t('app', 'Show'), 'name'=>'view', 'value'=>'view', 'style' => 'margin-right:10px;', ]);
},
'update' => function ($url, $model) {
return Html::a('<i class="glyphicon glyphicon-pencil"></i>',
$url, ['title' => Yii::t('app', 'Edit'), 'name'=>'update', 'style' => 'margin-right:10px;', ]);
},
'delete' => function ($url, $model) {
return Html::a('<i class="glyphicon glyphicon-trash"></i>',
$url, ['title' => Yii::t('app', 'Delete'), 'name'=>'delete', 'data-confirm'=>'Are you sure you want to delete this record?']);
}
]
],
],
]);
?>