protected function attachListenerOn(Application $app, $event, Closure $callback)
    {
        $app->make('events')->listen("orchestra.{$event}: extension.{$this->extension}", $callback);
    }
protected function attachListenerOn(Application $app, $event, Closure $callback)
    {
        $app->make('events')->listen("orchestra.{$event}: extension.{$this->extension}", $callback);
    }
protected function attachListenerOn ( Application $ app , $ event , Closure $ callback ) { $ app -> make ( 'events' ) -> listen ( "orchestra.{$event}: extension.{$this->extension}" , $ callback ) ; }
Attach event listener.

@param  \Illuminate\Contracts\Foundation\Application  $app
@param  string  $event
@param  \Closure  $callback

@return void
Attach event listener .