我正在尝试从https://laravel.com/docs/5.4/artisan使用Laravel progress bar
但我得到这下面的错误

(1/1) ErrorException
Undefined property: App\Http\Controllers\ImportDeviceController::$output

下面是我的代码：

$users = \App\Users::all();

    $bar = $this->output->createProgressBar(count($users));

    foreach ($users as $user) {
        $this->performTask($user);

        $bar->advance();
    }

    $bar->finish();

• • 更新日期：**

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Input;
use App\Http\Helpers\GlobalHelper;
use Illuminate\Support\Collection;
use App\Http\Helpers\ImportDeviceHelper;
use Illuminate\Support\Facades\Redirect;
use App\Http\Controllers\ImportController;
use Excel;
use XmlParser;
use Storage;
use Symfony\Component\Console\Helper\ProgressBar;


class ImportDeviceController extends Controller
{

    public function __construct(Request $request)
    {

        $this->objGlobalHelper = new GlobalHelper;
        $this->objImportDeviceHelper = new ImportDeviceHelper($request);
        $this->objImportController = new ImportController($request);
    }

    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */


    public function device()
    {
     $users = \App\Users::all();

    $bar = $this->output->createProgressBar(count($users));

    foreach ($users as $user) {
        $this->performTask($user);

        $bar->advance();
    }

    $bar->finish();

    exit;
 }