Magento 2: Implement UI Fileuploader

I follow this steps to add UI fileuploader component in admin form

I use UI fileuploader component to upload an icon for my FAQ extension. You can take reference from here: https://github.com/mageprince/magento2-FAQ

1) Add field in admin_form.xml(Admin Form)

<field name="icon">
    <argument name="data" xsi:type="array">
        <item name="config" xsi:type="array">
            <item name="dataType" xsi:type="string">string</item>
            <item name="source" xsi:type="string">FaqGroup</item>
            <item name="label" xsi:type="string" translate="true">Group Image</item>
            <item name="visible" xsi:type="boolean">true</item>
            <item name="formElement" xsi:type="string">fileUploader</item>
            <item name="elementTmpl" xsi:type="string">ui/form/element/uploader/uploader</item>
            <item name="previewTmpl" xsi:type="string">Vendor_Module/image-preview</item>
            <item name="required" xsi:type="boolean">false</item>
            <item name="sortOrder" xsi:type="number">40</item>
            <item name="uploaderConfig" xsi:type="array">
                <item name="url" xsi:type="url" path="your_router/faqgroup/upload"/>
            </item>
        </item>
    </argument>
</field>

2) Now we need to create controller which we define in uploaderConfig in admin form: <item name="url" xsi:type="url" path="vendor_module/faqgroup/upload"/>

app/code/Vendor/Module/Controller/Adminhtml/FaqGroup/Upload.php

<?php

namespace Vendor\Module\Controller\Adminhtml\FaqGroup;

use Magento\Framework\Controller\ResultFactory;

class Upload extends \Magento\Backend\App\Action
{
    public $imageUploader;

    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Vendor\Module\Model\ImageUploader $imageUploader
    ) {
        parent::__construct($context);
        $this->imageUploader = $imageUploader;
    }

    public function _isAllowed()
    {
        return $this->_authorization->isAllowed('Vendor_Module::Faq');
    }

    public function execute()
    {
        try {
            $result = $this->imageUploader->saveFileToTmpDir('icon');
            $result['cookie'] = [
                'name' => $this->_getSession()->getName(),
                'value' => $this->_getSession()->getSessionId(),
                'lifetime' => $this->_getSession()->getCookieLifetime(),
                'path' => $this->_getSession()->getCookiePath(),
                'domain' => $this->_getSession()->getCookieDomain(),
            ];
        } catch (\Exception $e) {
            $result = ['error' => $e->getMessage(), 'errorcode' => $e->getCode()];
        }
        return $this->resultFactory->create(ResultFactory::TYPE_JSON)->setData($result);
    }
}

3) Create ImageUploader.php

app/code/Vendor/Module/Model/ImageUploader.php

<?php

namespace Prince\Faq\Model;

class ImageUploader
{
    private $coreFileStorageDatabase;
    private $mediaDirectory;
    private $uploaderFactory;
    private $storeManager;
    private $logger;
    public $baseTmpPath;
    public $basePath;
    public $allowedExtensions;

    public function __construct(
        \Magento\MediaStorage\Helper\File\Storage\Database $coreFileStorageDatabase,
        \Magento\Framework\Filesystem $filesystem,
        \Magento\MediaStorage\Model\File\UploaderFactory $uploaderFactory,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        \Psr\Log\LoggerInterface $logger
    ) {
        $this->coreFileStorageDatabase = $coreFileStorageDatabase;
        $this->mediaDirectory = $filesystem->getDirectoryWrite(\Magento\Framework\App\Filesystem\DirectoryList::MEDIA);
        $this->uploaderFactory = $uploaderFactory;
        $this->storeManager = $storeManager;
        $this->logger = $logger;
        $this->baseTmpPath = "faq/tmp/icon";
        $this->basePath = "faq/icon";
        $this->allowedExtensions= ['jpg', 'jpeg', 'gif', 'png'];
    }

    public function setBaseTmpPath($baseTmpPath)
    {
        $this->baseTmpPath = $baseTmpPath;
    }

    public function setBasePath($basePath)
    {
        $this->basePath = $basePath;
    }

    public function setAllowedExtensions($allowedExtensions)
    {
        $this->allowedExtensions = $allowedExtensions;
    }

    public function getBaseTmpPath()
    {
        return $this->baseTmpPath;
    }

    public function getBasePath()
    {
        return $this->basePath;
    }

    public function getAllowedExtensions()
    {
        return $this->allowedExtensions;
    }

    public function getFilePath($path, $imageName)
    {
        return rtrim($path, '/') . '/' . ltrim($imageName, '/');
    }

    public function moveFileFromTmp($imageName)
    {
        $baseTmpPath = $this->getBaseTmpPath();
        $basePath = $this->getBasePath();
        $baseImagePath = $this->getFilePath($basePath, $imageName);
        $baseTmpImagePath = $this->getFilePath($baseTmpPath, $imageName);
        try {
            $this->coreFileStorageDatabase->copyFile(
                $baseTmpImagePath,
                $baseImagePath
            );
            $this->mediaDirectory->renameFile(
                $baseTmpImagePath,
                $baseImagePath
            );
        } catch (\Exception $e) {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('Something went wrong while saving the file(s).')
            );
        }
        return $imageName;
    }

    public function saveFileToTmpDir($fileId)
    {
        $baseTmpPath = $this->getBaseTmpPath();
        $uploader = $this->uploaderFactory->create(['fileId' => $fileId]);
        $uploader->setAllowedExtensions($this->getAllowedExtensions());
        $uploader->setAllowRenameFiles(true);
        $result = $uploader->save($this->mediaDirectory->getAbsolutePath($baseTmpPath));
        if (!$result) {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('File can not be saved to the destination folder.')
            );
        }

        $result['tmp_name'] = str_replace('\\', '/', $result['tmp_name']);
        $result['path'] = str_replace('\\', '/', $result['path']);
        $result['url'] = $this->storeManager
                ->getStore()
                ->getBaseUrl(
                    \Magento\Framework\UrlInterface::URL_TYPE_MEDIA
                ) . $this->getFilePath($baseTmpPath, $result['file']);
        $result['name'] = $result['file'];
        if (isset($result['file'])) {
            try {
                $relativePath = rtrim($baseTmpPath, '/') . '/' . ltrim($result['file'], '/');
                $this->coreFileStorageDatabase->saveFile($relativePath);
            } catch (\Exception $e) {
                $this->logger->critical($e);
                throw new \Magento\Framework\Exception\LocalizedException(
                    __('Something went wrong while saving the file(s).')
                );
            }
        }
        return $result;
    }
}

4) Create image-preview.html

app/code/Vendor/Module/view/adminhtml/web/template/image-preview.html

<div class="file-uploader-summary">
    <div class="file-uploader-preview">
        <a attr="href: $parent.getFilePreview($file)" target="_blank">
            <img
                class="preview-image"
                tabindex="0"
                event="load: $parent.onPreviewLoad.bind($parent)"
                attr="
                    src: $parent.getFilePreview($file),
                    alt: $file.name">
        </a>

        <div class="actions">
            <button
                type="button"
                class="action-remove"
                data-role="delete-button"
                attr="title: $t('Delete image')"
                click="$parent.removeFile.bind($parent, $file)">
                <span translate="'Delete image'"/>
            </button>
        </div>
    </div>

    <div class="file-uploader-filename" text="$file.name"/>
    <div class="file-uploader-meta">
        <text args="$file.previewWidth"/>x<text args="$file.previewHeight"/>
    </div>
</div>

5) Now add arguments for ImageUploader.php in di.xml

app/code/Vendor/Module/etc/di.xml

<type name="Vendor\Module\Model\ImageUploader">
    <arguments>
        <!-- Temporary file stored in pub/media/faq/tmp/icon -->
        <argument name="baseTmpPath" xsi:type="string">faq/tmp/icon</argument>
        <argument name="basePath" xsi:type="string">faq/icon</argument>
        <argument name="allowedExtensions" xsi:type="array">
            <item name="jpg" xsi:type="string">jpg</item>
            <item name="jpeg" xsi:type="string">jpeg</item>
            <item name="gif" xsi:type="string">gif</item>
            <item name="png" xsi:type="string">png</item>
        </argument>
    </arguments>
</type>

Check this file for load uploaded image on edit form: DataProvider.php

OUTPUT:

enter image description here

To save image in database

app/code/Vendor/Module/Controller/Adminhtml/Save.php

<?php

namespace Vendor\Module\Controller\Adminhtml;

use Magento\Framework\Exception\LocalizedException;

class Save extends \Magento\Backend\App\Action
{
    protected $dataPersistor;

    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\App\Request\DataPersistorInterface $dataPersistor
    ) {
        $this->dataPersistor = $dataPersistor;
        parent::__construct($context);
    }

    public function execute()
    {
        ...
        ...
        $data = $this->_filterFoodData($data);
        $model->setData($data);
        $model->save();
        ...
        ...     
    }

    public function _filterFoodData(array $rawData)
    {
        //Replace icon with fileuploader field name
        $data = $rawData;
        if (isset($data['icon'][0]['name'])) {
            $data['icon'] = $data['icon'][0]['name'];
        } else {
            $data['icon'] = null;
        }
        return $data;
    }
}

To show uploaded image in form edit page:

app/code/Vendor/Module/Model/DataProvider.php

<?php

namespace Vendor\Module\Model;

use Magento\Store\Model\StoreManagerInterface;

class DataProvider extends \Magento\Ui\DataProvider\AbstractDataProvider
{
    ...
    ...

    public function getData()
    {
        ...
        ...
        $items = $this->collection->getItems();

        //Replace icon with fileuploader field name
        foreach ($items as $model) {
            $this->loadedData[$model->getId()] = $model->getData();
            if ($model->getIcon()) {
                $m['icon'][0]['name'] = $model->getIcon();
                $m['icon'][0]['url'] = $this->getMediaUrl().$model->getIcon();
                $fullData = $this->loadedData;
                $this->loadedData[$model->getId()] = array_merge($fullData[$model->getId()], $m);
            }
        }
        ...
        ...

        return $this->loadedData;
    }

    public function getMediaUrl()
    {
        $mediaUrl = $this->storeManager->getStore()
            ->getBaseUrl(\Magento\Framework\UrlInterface::URL_TYPE_MEDIA).'faq/tmp/icon/';
        return $mediaUrl;
    }
}

Supplement for Magento 2.2 UI component

Compare with Magento 2.1, in Magento 2.2, the UI component had some optional differences like below. We could make use of the official Magento_Catalog/image-preview as preview templete, and the rest of codes like controller could refer to the accepted answer.

<field name="image" formElement="fileUploader">
    <settings>
        <notice translate="true">Allowed file types: jpg, jpeg, gif, png.</notice>
        <label translate="true">Image</label>
        <componentType>fileUploader</componentType>
    </settings>
    <formElements>
        <fileUploader>
            <settings>
                <allowedExtensions>jpg jpeg gif png</allowedExtensions>
                <maxFileSize>10240000</maxFileSize>
                <placeholderType>image</placeholderType>
                <previewTmpl>Magento_Catalog/image-preview</previewTmpl>
                <uploaderConfig>
                    <param xsi:type="string" name="url">path/to/controller</param>
                </uploaderConfig>
            </settings>
        </fileUploader>
    </formElements>
</field>