上下文绑定报错

参考文档编写的代码 但是报错

    Target [App\\Http\\Services\\SnsLogin\\Contract\\SnsloginInterface] is not instantiable while building [App\\Http\\Controllers\\V1\\Auth\\WechatloginController]

controller代码

<?php

namespace App\Http\Controllers\v1\Auth;

use App\Http\Controllers\Controller;

use App\Http\Requests\Auth\AuthRequest;
use App\Http\Services\SnsLogin\Contract\SnsloginInterface;
use App\Http\Services\SnsLogin\WechatloginService;
use Illuminate\Http\Request;

class WechatloginController extends Controller
{
    private $snslogin;

    public function __construct(SnsloginInterface $snslogin)
    {
        $this->snslogin = $snslogin;
    }

    //
    public function login(AuthRequest $request)
    {
        $request->validate('wechat_login');
        $this->snslogin -> login($request->code);
    }
}

服务容器代码

/**
     * Register services.
     *
     * @return void
     */
    public function register()
    {
        /**bind方法好用**/
        /*$this->app->bind(
            SnsloginInterface::class,
            WechatloginService::class,
        );*/

        /**上下文绑定报错**/
        $this->app->when(WechatloginController::class)
            ->needs(SnsloginInterface::class)
            ->give(function () {
                return new WechatloginService();
            });

    }

    /**
     * Bootstrap services.
     *
     * @return void
     */
    public function boot()
    {
        //

        /*$this->app->when(WechatloginController::class)
            ->needs(SnsloginInterface::class)
            ->give(WechatloginService::class);*/

    }

问题： bing方法好用 表示我的 接口 和 现实是没问题的。但是使用上下文绑定 就会报错 参考了文档 没发现问题！