[Solved] Magento 2: Implement UI Fileuploader

hallleron Asks: Magento 2: Implement UI Fileuploader
I recently implemented the FileUploader Ui Component in my form on Magento 2.1.7.

The code for it is here (app/code/Vendor/Blog/view/adminhtml/ui_component/vendor_blog_form.xml):

Code:
<field name="featured_images">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="dataType" xsi:type="string">text</item>
                    <item name="label" translate="true" xsi:type="string">Hervorgehobene Bilder:</item>
                    <item name="formElement" xsi:type="string">fileUploader</item>
                    <item name="componentType" xsi:type="string">fileUploader</item>
                    <item name="previewTmpl" xsi:type="string">Magento_Catalog/image-preview</item>
                    <item name="elementTmpl" xsi:type="string">ui/form/element/uploader/uploader</item>
                    <item name="allowedExtensions" xsi:type="string">jpg jpeg gif png</item>
                    <item name="notice" xsi:type="string" translate="true">Erlaubte Dateitypen: png, gif, jpg, jpeg.</item>
                    <item name="maxFileSize" xsi:type="number">2097152</item>
                    <item name="source" xsi:type="string">blog</item>
                    <item name="sortOrder" xsi:type="number">10</item>
                    <item name="dataScope" xsi:type="string">featured_images</item>
                    <item name="validation" xsi:type="array">
                        <item name="required-entry" xsi:type="boolean">false</item>
                    </item>
                    <item name="uploaderConfig" xsi:type="array">
                        <item name="url" xsi:type="url" path="vendor_blog/blog/upload"/>
                    </item>
                </item>
            </argument>
        </field>

My Controller for it is this (app/code/Vendor/Blog/Controller/Adminhtml/Blog/Upload.php):

Code:
<?php

namespace VendorBlogControllerAdminhtmlBlog;

use MagentoFrameworkAppFilesystemDirectoryList;
use MagentoBackendAppAction;  

class Upload extends VendorBlogControllerAdminhtmlBlog
{

    protected $_fileUploaderFactory;
    protected $_directory_list;
    protected $_logger;

    public function __construct(
        ActionContext $context,
        MagentoFrameworkRegistry $coreRegistry,
        MagentoMediaStorageModelFileUploaderFactory $fileUploaderFactory,
        MagentoFrameworkAppFilesystemDirectoryList $directory_list,
        PsrLogLoggerInterface $logger
    ) {
        $this->_fileUploaderFactory = $fileUploaderFactory;
        $this->_directory_list = $directory_list;
        $this->_logger = $logger;
        parent::__construct($context, $coreRegistry);
    }

    public function execute(){
        $uploader = $this->_fileUploaderFactory->create(['fileId' => 'featured_images']);
        $uploader->setAllowedExtensions(['jpg', 'jpeg', 'gif', 'png']);
        $uploader->setAllowRenameFiles(false);
        $uploader->setFilesDispersion(false);
        $path = $this->_filesystem->getDirectoryRead(DirectoryList::MEDIA)->getAbsolutePath('blog');
        //$path = $this->_directory_list->getPath('media') . '/blog';
        $this->_logger->debug('Uploader.php: '.$path);
        $uploader->save($path);
    }
}

However, when I upload an image and inspect the call in Chrome’s console, I get an Error 500 with Exception: $_FILES array is empty.

I am struggling for two days but I can’t get it to work right. When I uncomment the alternate $path variable line, the Upload succeeds but I do not get a preview.

I read that it might be the enctype of the form that’s causing the issue, but I didn’t find any information on how to check this for a UI Component form.

If you need the whole exception code please let me know.

I appreciate every help possible. Thank you!

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