class FeedItemsDeleteForm

class FeedItemsDeleteForm extends ContentEntityConfirmFormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getQuestion() {
        return $this->t('Are you sure you want to delete all items from the feed %feed?', [
            '%feed' => $this->entity
                ->label(),
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCancelUrl() {
        return new Url('aggregator.admin_overview');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfirmText() {
        return $this->t('Delete items');
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->entity
            ->deleteItems();
        $form_state->setRedirectUrl($this->getCancelUrl());
    }

}