FCE to create a linklist with possibilty to choose how target is defined (internal by Page, external by url and filereferences with download) Also Solution for a downloadAction to serve files for download through a controllerAction

Appendixes.html

{namespace flux=Tx_Flux_ViewHelpers}
{namespace v=Tx_Vhs_ViewHelpers}
{namespace w=Tx_Fluidwidget_ViewHelpers}
<f:layout name="Content"/>
<f:section name="Configuration">
  <flux:flexform id="appendixes" label="Appendixes" wizardTab="PRISMA">
		<flux:flexform.section name="appendixes" label="Anhänge / Verweise">
			<flux:flexform.object name="appendix" label="Anhang / Verweis">
				<flux:flexform.field.select name="linkType" label="Verweistyp" items="{page:'Interner Verweis',url:'Externer Verweis beginnend mit http://',filereference:'Dateianhang'}"></flux:flexform.field.select>
				<flux:flexform.field.select name="linkIcon" label="Link Icon" items="{0:'kein Icon',calendar:'Kalender',bubble:'Sprechblase'}"></flux:flexform.field.select>
				<flux:flexform.field.input name="linkTitle" label="Link Titel"/>
				<flux:flexform.field.file name="filereference" label="Dateianhang" size="1" minItems="0" maxItems="1" displayCond="<![CDATA[FIELD:linkType:=:filereference]]>"/>
				<flux:flexform.field.input name="page" label="Interner Verweis" displayCond="<![CDATA[FIELD:linkType:=:page]]>">
					<flux:flexform.field.wizard.link label="Linkziel wählen" activeTab="pages" />
				</flux:flexform.field.input>
				<flux:flexform.field.input name="url" label="Externer Verweis" displayCond="<![CDATA[FIELD:linkType:=:url]]>"/>
				<flux:flexform.field.custom name="warning" displayCond="<![CDATA[FIELD:linkType:REQ:FALSE]]>">
					<strong style="color: red;">Please save the record configure link target.</strong>
				</flux:flexform.field.custom>
			</flux:flexform.object>
		</flux:flexform.section>	
	</flux:flexform>
</f:section>

<f:section name="Preview">
	<f:for each="{appendixes}" as="single">
		{single.appendix.linkTitle}<br>
	</f:for>
</f:section>

<f:section name="Resources">
</f:section>

<f:section name="Appendix">
	<v:switch value="{single.appendix.linkType}">
	    <v:case case="page" break="TRUE">
	        <a href="{f:uri.page(pageUid:single.appendix.page)}" title="{single.appendix.linkTitle}">{single.appendix.linkIcon->v:format.prepend(add:'<i class="icon-prisma-')->v:format.append(add:'"></i> ')->f:if(condition:single.appendix.linkIcon)} <strong>{single.appendix.linkTitle}</strong></a>
	    </v:case>
	     <v:case case="url" break="TRUE">
	        <a href="{single.appendix.url}" title="{single.appendix.linkTitle}">{single.appendix.linkIcon->v:format.prepend(add:'<i class="icon-prisma-')->v:format.append(add:'"></i> ')->f:if(condition:single.appendix.linkIcon)} <strong>{single.appendix.linkTitle}</strong></a>
	    </v:case>
	    <v:case case="filereference" break="TRUE">
	        <f:link.action controller="Task" pluginName="Task" action="download" extensionName="prisma" arguments="{target:single.appendix.filereference,mode:'passthrough'}">{single.appendix.linkIcon->v:format.prepend(add:'<i class="icon-prisma-')->v:format.append(add:'"></i> ')->f:if(condition:single.appendix.linkIcon)} <strong>{single.appendix.linkTitle}</strong></f:link.action>
	    </v:case>
	</v:switch>
</f:section>

<f:section name="Main">
	<div class="appendixes">
		<f:if condition="{appendixes->f:count()}>1">
			<f:then>
				<ul class="unstyled">
					<f:for each="{appendixes}" as="single">
						<li>
							<f:render section="Appendix" arguments="{single:single}" />
						</li>
					</f:for>
				</ul>
			</f:then>
			<f:else>
				<f:for each="{appendixes}" as="single">
					<f:render section="Appendix" arguments="{single:single}" />
				</f:for>
			</f:else>
		</f:if>
	</div>
</f:section>

setup.txt (Typoscript Setup)

# make TaskController available
lib.prismatasks = USER
lib.prismatasks { 
        userFunc = TYPO3\CMS\Extbase\Core\Bootstrap->run
        pluginName = Task
        extensionName = Prisma
        controller = Task
        vendorName = Codearts
        action={GP:tx_prisma_task|action}
        settings =< plugin.tx_prisma.settings
        persistence =< plugin.tx_prisma.persistence
        view =< plugin.tx_prisma.view
}

page.9999999 = COA
page.9999999 { 
  10 =< lib.prismatasks
}

TaskController.php

<?php
namespace Codearts\Prisma\Controller;

/***************************************************************
 *  Copyright notice
*
*  (c) 2013 Benjamin Rau <rau@codearts.at>, Interwall
*
*  All rights reserved
*
*  This script is part of the TYPO3 project. The TYPO3 project is
*  free software; you can redistribute it and/or modify
*  it under the terms of the GNU General Public License as published by
*  the Free Software Foundation; either version 3 of the License, or
*  (at your option) any later version.
*
*  The GNU General Public License can be found at
*  http://www.gnu.org/copyleft/gpl.html.
*
*  This script is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  This copyright notice MUST APPEAR in all copies of the script!
***************************************************************/

/**
 *
 *
 * @package prisma
 * @license http://www.gnu.org/licenses/gpl.html GNU General Public License, version 3 or later
*
*/
class TaskController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController {
  
	public function defaultAction() {
		
	}
	
	/**
	 * downloadAction
	 * 
	 * @param string $target
	 * @param string $mode
	 * @return string
	 */
	public function downloadAction($target=NULL, $mode='basic') {
		if ($mode != 'passthrough') {
			header('Location: ' . $target);
		} else {
			$absoluteTargetPath = \t3lib_div::getFileAbsFileName($target);
			if (strstr($_SERVER['HTTP_USER_AGENT'], 'MSIE')) {
				header('Pragma: public');
				header('Expires: 0');
				header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
				header('Content-type: application-download');
				header('Content-length: ' . filesize($absoluteTargetPath));
				header('Content-Transfer-Encoding: binary');
			} else {
				header('Content-type: ' . mime_content_type($absoluteTargetPath));
			}
			$handle = fopen($absoluteTargetPath, 'rb');
			$chunkSize = 1048576;
			header('Content-disposition: attachment; filename="' . basename($absoluteTargetPath) . '"');
			while (FALSE === feof($handle)) {
				echo fread($handle, $chunkSize);
				ob_flush();
				flush();
			}
			fclose($handle);
		}
		exit();
	}
}

I don't think that

displayCond="<![CDATA[FIELD:linkType:=:url]]>"

is working, because the field "linkType" is in a flux:flexform.object, it's not on the first level. That's why it should be something like

displayCond="<![CDATA[FIELD:appendixes.appendix.linkType:=:url]]>"

(but this is also not working)