framework/web/UploadedFile.php
public static function getInstanceByName($name)
    {
        $files = self::loadFiles();
        return isset($files[$name]) ? new static($files[$name]) : null;
    }
public static function getInstanceByName($name)
    {
        $files = self::loadFiles();
        return isset($files[$name]) ? new static($files[$name]) : null;
    }
Returns an uploaded file according to the given file input name.
The name can be a plain string or a string like an array element (e.g. 'Post[imageFile]', or 'Post[0][imageFile]').
@param string $name the name of the file input field.
@return null|UploadedFile the instance of the uploaded file.
Null is returned if no file is uploaded for the specified name.