Undefined Property in Notification toMail()

[chaowen112]

Hi, I'm using L5.6 now and trying to send email through notifications.

The following is my Notification class.

class VisitApplyResult extends Notification implements ShouldQueue
{
    use Queueable;

    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct($approval)
    {
        $this->approval = $approval;
        Log::info($this->approval);
        // Successfully print out here
    }

    /**
     * Get the notification's delivery channels.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function via($notifiable)
    {
        return ['mail'];
    }

    /**
     * Get the mail representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return \Illuminate\Notifications\Messages\MailMessage
     */
    public function toMail($notifiable)
    {

        Log::info($this->application);
        // Error here, Undefined property: App\Notifications\VisitApplyResult::$approval
        
        return (new MailMessage)
                    ->subject('Subject')
                    ->line($this->approval);
    }

    /**
     * Get the array representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function toArray($notifiable)
    {
        return [
            //
        ];
    }
}

And I use the class in the controller like

Notification::route('mail', [$apply->email])
        ->notify(new VisitApplyResult(VisitApplication::find($request['id'])->approval));

I doubted if queueing is the issue since it takes a long time to send the email, but no matter using database queue or sync, both run into the same error.
I tried to log the variable in the constructor, and it successfully prints out what I want. But I can't access the same variable in other functions. Could anyone help?

Thanks.

[GrahamCampbell]

Laravel 5.6 is no longer supported (for a long time).