Yii2为什么没有出现野外表格？

I have this code in my _form.php

<?= $form->field($model, 'receiver_id')->widget(Select2::classname(),[
    'data'=>ArrayHelper::map(User::findAll(['category' => 'customer']),'username','username'),
    'language' => 'en',
    'options' => ['placeholder' => 'select student id ...'],
    'pluginOptions' => [
        'allowClear' => true
        ],

 ]); ?>

its working fine at first but when I add this layout code in the controller it didn't show the dropdown

public function actionCreate()
{    $this->layout = 'lecLayout';
    $model = new Privatemessage();

    if ($model->load(Yii::$app->request->post()) && $model->save()) {
        return $this->redirect(['view', 'id' => $model->id]);
    }

    return $this->render('create', [
        'model' => $model,
    ]);
}

if i do not put the layout code its working fine. but i need the form display in the layout.