使用create form进行Laravel验证:为下拉框检索旧输入数据

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Validator;

public function store(Request $request)
{
    $validator = Validator::make($request->all(), [
        'dropdown' => 'required',
    ]);

    // 如果验证失败，重定向回表单，并将错误信息闪存到Session中
    if ($validator->fails()) {
        return redirect()->back()->withErrors($validator)->withInput();
    }

    // 如果验证成功，继续处理其他逻辑
    // ...
}

<form method="POST" action="{{ route('store') }}">
    @csrf

    <select name="dropdown">
        <option value="1" {{ old('dropdown') == 1 ? 'selected' : '' }}>选项1</option>
        <option value="2" {{ old('dropdown') == 2 ? 'selected' : '' }}>选项2</option>
        <option value="3" {{ old('dropdown') == 3 ? 'selected' : '' }}>选项3</option>
    </select>

    @error('dropdown')
        <div>{{ $message }}</div>
    @enderror

    <button type="submit">提交</button>
</form>