"；无法解决的依赖关系解析“；错误，Laravel服务提供商

我正在尝试构建一个自定义的Service Provider包，但遇到了以下错误。有人有这方面的经验吗？

Unresolvable dependency resolving [Parameter #0 [ <required> $app ]] in class Illuminate'Support'ServiceProvider

包文件夹结构：

[root]
....packages/
........mbarwick83/
............previewr/
................src/
....................PreviewrServiceProvider.php
....................Previewr.php
................composer.json

config/app.hp:

Mbarwick83'Previewr'PreviewrServiceProvider::class

服务提供商：

<?php
namespace Mbarwick83'Previewr;
use Illuminate'Support'ServiceProvider;
class PreviewrServiceProvider extends ServiceProvider
{
    /**
     * Indicates if loading of the provider is deferred.
     *
     * @var bool
     */
    protected $defer = false;
    /**
     * Perform post-registration booting of services.
     *
     * @return void
     */
    public function boot()
    {
        //
    }
    /**
     * Register any package services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->bind('Mbarwick83'Previewr'Previewr',function($app){
            return new Previewr($app);
        });
    }
}

Previewr.php（类）:

<?php
namespace Mbarwick83'Previewr;
class Previewr
{
    /**
     * Create a new Previewr Instance
     */
    public function __construct()
    {
        //
    }
    /**
     * Friendly welcome
     *
     * @param string $phrase Phrase to return
     *
     * @return string Returns the phrase passed in
     */
    public function something($phrase)
    {
        return $phrase;
    }
}
Controller/view:
use Mbarwick83'Previewr'PreviewrServiceProvider as Previewr;
public function index(Previewr $previewr)
{
    echo $previewr->something('Hello, League!');
}

composer.json:

"autoload": {
        "psr-4": {
            "Mbarwick83''Previewr''": "packages/Mbarwick83/Previewr/src"
        }
    },