Code to handle File Input Validation inside Model in Yii2 Multiple Input widget

model.php

<?php

/*#############################
* Developer: Mohammad Sharaf Ali
* Designation: Web Developer
* Version: 1.0
*/#############################

/* REQUIREMENTS
 * https://github.com/unclead/yii2-multiple-input
 * All code to be placed inside your Model Class
 */

const FILE_ALLOWED_EXT = ['pdf', 'xls', 'xlsx', 'doc', 'docx', 'jpp', 'jpeg', 'png'];
const FILE_ALLOWED_SIZE = 1024 * 1024 * 20; // 20 MB

public $allowedMidDocFiles;

public function validateFile()
{
    $successFlag = true;

    foreach ($_FILES['Middocuments'] as $key => $value) {
        foreach ($value['allowedMidDocFiles'] as $file) {
            $_FILES['Middocuments'][$key]['uploadFile'][] = $file['uploadFile'];
        }

        unset($_FILES['Middocuments'][$key]['allowedMidDocFiles']);
    }

    $files = UploadedFile::getInstances($this, 'uploadFile');

    if (!empty($files)) {
        foreach ($files as $index => $file) {
            $error = null;

            $fileValidator = new FileValidator();
            $fileValidator->skipOnEmpty = false;
            $fileValidator->checkExtensionByMimeType = false;
            $fileValidator->extensions = self::FILE_ALLOWED_EXT;
            $fileValidator->maxSize = self::FILE_ALLOWED_SIZE;
            $fileValidator->validate($file, $error);

            if (!empty($error)) {
                $successFlag = false;

                $key = 'allowedMidDocFiles[' . $index . '][uploadFile]';
                $this->addError($key, $error);
            }
        }
    }

    return $successFlag;
}