首先看下github中的说明
配置跳过
然后是向html类中添加此插件

namespace app\components;

use yii\helpers\Html as BaseHtml;
use sweelix\yii2\plupload\traits\Plupload;

class Html extends BaseHtml
{
    // adding this trait allow easy access to plupload
    use Plupload;
}

这里在类中use Plupload；
他映射的类是插件下/traits/Plupload.php
看下这个文件的代码可以找到使用时的

echo Html::asyncInput('demoUpload', isset($_POST['demoUpload'])?$_POST['demoUpload']:null, ['config' => [
        'ui' => true,
        'auto' => true,
    ]]); ?>

asyncInput方法

 /**
     * Create an asynchronous file upload.
     * Plupload specific configuration should be set in $options['config']
     * The $options['config']['ui'] can be :
     *  * false // no ui
     *  * true  // basic ui
     *  * Javascript object (passed in Jsexpression). Everything is handled by the developper
     *
     * @param  string       $name    name of the input (append [] for multifile upload)
     * @param  string|array $value   the file(s) already uploaded (array for multifile upload)
     * @param  array        $options @see static::input()
     *
     * @return string
     * @since  1.0.0
     */
    public static function asyncInput($name, $value = null, $options = [])
    {
        // prepare data
        $originalName = $name;
        if (is_array($value) === true) {
            $value = array_filter($value, function ($el) { return !empty($el); });
        }
        if (empty($value) === true) {
            $value = null;
        }
        // prepare option data
        $options['name'] = $name;
        $options['config']['multiSelection'] = false;
        if (isset($options['id']) === false) {
            $options['id'] = self::getIdByName($name);
        }
        // remove the trailing [] which is just annoying except to send multiple files
        // we rely on [] to define the multiple file upload
        if (substr($name, -2) === '[]') {
            $originalName = substr($name, 0, -2);
            $options['config']['multiSelection'] = true;
            if ($value !== null) {
                if (is_array($value) === false) {
                    // force array for multifile
                    $value = [$value];
                }
                $value = array_map(function ($el) {
                    // remove everything which is path related. It must be handled by the developper / model
                    return pathinfo(trim($el), PATHINFO_BASENAME);
                }, $value);
            }
        } else {
            if ($value !== null) {
                $value = pathinfo((string)$value, PATHINFO_BASENAME);
            }
        }
        if ($value !== null) {
            // we must retrieve original data
            $instances = UploadedFile::getInstancesByName($originalName);
            // force check with arrays
            $affectedFiles = (is_array($value) === true)?$value:[$value];
            //translate everything into UploadedFile(s)
            $translatedValues = [];
            foreach ($instances as $instance) {
                if (in_array($instance->name, $affectedFiles) === true) {
                    $affectedFilesKeys = array_keys($affectedFiles, $instance->name);
                    unset($affectedFiles[$affectedFilesKeys[0]]);
                    $translatedValues[] = $instance;
                }
            }
            foreach ($affectedFiles as $remainingFile) {
                // we are looking at already saved files. Reinit as expected
                $translatedValues[] = new UploadedFile([
                    'name' => $remainingFile,
                    'tempName' => null,
                    'type' => 'application/octet-stream',
                    'size' => null,
                    'error' => 0,
                ]);
            }
            $value = $translatedValues;
            if ($options['config']['multiSelection'] === false) {
                // get first value in case we are not multi
                $value = array_pop($value);
            }
        }
        $config = static::prepareAsyncInput($options);
        return static::renderAsyncInput($value, $options, $config);
    }

 * @param  string       $name    name of the input (append [] for multifile upload)
 * @param  string|array $value   the file(s) already uploaded (array for multifile upload)
 * @param  array        $options @see static::input()

asyncInput($name, $value = null, $options = [])
看方法的参数说明
第一个参数是插件的name名称
第二个参数就是你所需要的已上传文件显示
单个文件传入文件路径字符串
多个文件传入路径数组
第三个参数不用多说，当前html元素要附件的属性
这样明白了吗？这个插件我没用过，不知道是否好用？