kartik\export\ExportMenu::init PHP Method

    public function init()
    {
        if (empty($this->options['id'])) {
            $this->options['id'] = $this->getId();
        }
        if (empty($this->exportRequestParam)) {
            $this->exportRequestParam = 'exportFull_' . $this->options['id'];
        }
        $this->_columnSelectorEnabled = $this->showColumnSelector && $this->asDropdown;
        $this->_triggerDownload = !empty($_POST) && !empty($_POST[$this->exportRequestParam]) && $_POST[$this->exportRequestParam];
        $this->_doNotStream = !$this->stream && !$this->streamAfterSave;
        if ($this->_doNotStream) {
            $this->target = self::TARGET_SELF;
        }
        if ($this->_triggerDownload) {
            if (!$this->_doNotStream) {
                Yii::$app->controller->layout = false;
            }
            $this->_exportType = $_POST[self::PARAM_EXPORT_TYPE];
            $this->_columnSelectorEnabled = $_POST[self::PARAM_COLSEL_FLAG];
            $this->initSelectedColumns();
        }
        if ($this->dynagrid) {
            $this->_columnSelectorEnabled = false;
            $options = $this->dynagridOptions;
            $options['columns'] = $this->columns;
            $options['storage'] = 'db';
            $options['gridOptions']['dataProvider'] = $this->dataProvider;
            $dynagrid = new DynaGrid($options);
            $this->columns = $dynagrid->getColumns();
        }
        parent::init();
    }