namespace app\models;

use yii\base\Model;
use yii\web\UploadedFile;

/**
* UploadForm is the model behind the upload form.
*/
class UploadForm extends Model
{
 /**
 * @var UploadedFile file attribute
 */
 public $file;

 /**
 * @return array the validation rules.
 */
 public function rules()
 {
  return [
   [['file'], ‘file'],
  ];
 }
}

<?php
use yii\widgets\ActiveForm;
?>

<?php $form = ActiveForm::begin([‘options' => ['enctype' => 'multipart/form-data']]) ?>

<?= $form->field($model, ‘file')->fileInput() ?>

<button>Submit</button>

<?php ActiveForm::end() ?>

use app\models\UploadForm;
use yii\web\UploadedFile;



public function actionUpload()
{
 $model = new UploadForm();

 if (Yii::$app->request->isPost) {
  $model->file = UploadedFile::getInstance($model, ‘file');

  if ($model->file && $model->validate()) {
   $model->file->saveAs(‘uploads/' . $model->file->baseName . ‘.' . $model->file->extension);
  }
 }

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