yii\bootstrap\ButtonDropdown::renderButton PHP Method

    protected function renderButton()
    {
        Html::addCssClass($this->options, ['widget' => 'btn']);
        $label = $this->label;
        if ($this->encodeLabel) {
            $label = Html::encode($label);
        }
        if ($this->split) {
            $options = $this->options;
            $this->options['data-toggle'] = 'dropdown';
            Html::addCssClass($this->options, ['toggle' => 'dropdown-toggle']);
            unset($this->options['id']);
            $splitButton = Button::widget(['label' => '<span class="caret"></span>', 'encodeLabel' => false, 'options' => $this->options, 'view' => $this->getView()]);
        } else {
            $label .= ' <span class="caret"></span>';
            $options = $this->options;
            if (!isset($options['href']) && $this->tagName === 'a') {
                $options['href'] = '#';
            }
            Html::addCssClass($options, ['toggle' => 'dropdown-toggle']);
            $options['data-toggle'] = 'dropdown';
            $splitButton = '';
        }
        return Button::widget(['tagName' => $this->tagName, 'label' => $label, 'options' => $options, 'encodeLabel' => false, 'view' => $this->getView()]) . "\n" . $splitButton;
    }