.php### 场景

表单验证失败展示错误提示是一个经常遇到,下面简单的看一看laravel是做的

分析

make:auth 生成的原始的用户的注册register.blade.php是怎么做的呢?

                        <div class="form-group{{ $errors->has('name') ? ' has-error' : '' }}">
                            <label for="name" class="col-md-4 control-label">用户名</label>

                            <div class="col-md-6">
                                <input id="name" type="text" class="form-control" name="name" value="{{ old('name') }}" required autofocus>

                                @if ($errors->has('name'))
                                    <span class="help-block">
                                        <strong>{{ $errors->first('name') }}</strong>
                                    </span>
                                @endif
                            </div>
                        </div>

可以看到是是通过$errors变量， `$errors` 是每个view视图都存在, 它是Illuminate\Support\MesaageBag实例，也是一次性的Session信息, laravel总是会检查Session的错误信息,如果存在的话 则绑定到视图视图

$errrors 是怎么传递的呢?

web的中间件 \Illuminate\View\Middleware\ShareErrorsFromSession::class
下面奉上这个中间件的源码, 可以看到这个中间件，做了一个很简单的操作, session中如果存在
 key为errors的量 则

namespace Illuminate\View\Middleware;

use Closure;
use Illuminate\Support\ViewErrorBag;
use Illuminate\Contracts\View\Factory as ViewFactory;

class ShareErrorsFromSession
{
    /**
     * The view factory implementation.
     *
     * @var \Illuminate\Contracts\View\Factory
     */
    protected $view;

    /**
     * Create a new error binder instance.
     *
     * @param  \Illuminate\Contracts\View\Factory  $view
     * @return void
     */
    public function __construct(ViewFactory $view)
    {
        $this->view = $view;
    }

    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        // If the current session has an "errors" variable bound to it, we will share
        // its value with all view instances so the views can easily access errors
        // without having to bind. An empty bag is set when there aren't errors.
        $this->view->share(
            'errors', $request->session()->get('errors') ?: new ViewErrorBag
        );

        // Putting the errors in the view for every view allows the developer to just
        // assume that some errors are always available, which is convenient since
        // they don't have to continually run checks for the presence of errors.

        return $next($request);
    }
}

最简单的写法表单反馈

上面register.blade.php可以看到源码的展示是很精细的, 但是这样的话 代码书写的速度上会慢一点，如果站点对样式的要求不是特别苛刻的话 可以考虑下面的写法。批量处理的版本

        <div class="row">
            <div class="col-md-8 col-md-offset-2">
                @if($errors->any())
                    <ol class="alert alert-danger">
                        @foreach($errors->all() as $error)
                            <li>{{ $error }}</li>
                        @endforeach
                    </ol>
                @endif
            </div>
        </div>