尝试从IOC容器实例化依赖项时未定义的属性异常

Question

I'm trying to deepen my knowlade in laravel architecture.

1. I have a search engine (elastic search for the sake of the example), but this search engine might change in the future. So im trying to write a container for this, so in case i'll change the engine in the future, i will have to change only the container. (I believe the termenology is factory design?)

2. I have created a provider app/providers/DataFromSearchEngine.php that looks like this:

   use Illuminate\Support\ServiceProvider;
   
   class DataFromSearchEngine extends ServiceProvider {
      public function boot()
      {
       //
      }
   
      public function register()
     {
       $this->app->singleton('SearchEngine', function($app) {
          return new elasticSearch; 
       });
     }
   
   }
   

3. Then i registered it in the providers array in config/app.php .

   'providers' => [
       // providers...
   
       'App\Providers\DataFromSearchEngine'
   ],
   

4. The next step is to call SearchEngine from my controller:

   namespace App\Http\Controllers;
   
   use App\Http\Requests;
   use App\Http\Controllers\Controller;
   use Illuminate\Http\Request;
   
   class SearchController extends Controller {
   
      protected $searchEngine;
   
      public function __construct() {
         $this->searchEngine = $this->app->make('SearchEngine');
      }
   
   }
   

But all these yields: Undefined property: App\Http\Controllers\SearchController::$app

Can someone explain what i'm missing?

Answer 1

Instead of using $this->app try using app().

This is because non of the inherited controller classes, i.e. App\Http\Controllers\Controller or Illuminate\Routing\Controllers\Controller have an app property on them.

As a note you can use app('SearchEngine') which is the equivalent of app()->make('SearchEngine') as a shortcut to making your object.