如何在C＃中创建类对象列表的数组

我的C＃类别如下

public class SeatPlans
{
    public int Id { get; set; }
    public string seat_id { get; set; }
    public string seat_no { get; set; }
    public int layout_id { get; set; }
}

我创建了一个类对象列表，如下所示

List<SeatPlans> allUser = new List<SeatPlans>();

但我需要的是列表的数组，这样我可以访问诸如几个对象的数据allUser[0]，allUser[1]，allUser[2]

我的控制器代码如下

public JsonResult getdata(int seat_plane_id)
{
    int lid = seat_plane_id;
    layoutsController L = new layoutsController();
    JsonResult result = L.getlayouts(lid);

    List<layouts> L1 = (List<layouts>)result.Data;
    List<List<SeatPlans>> allUser = new List<List<SeatPlans>>();

    for (int i = 0; i < L1.Count; i++)
    {
        String lid1 = L1[i].ticket_no_start;
        lid = Int32.Parse(lid1);
        allUser[i] = db.SEATPLAN.Where(d => d.layout_id == lid).ToList();
    }

    var v = new { allUser = allUser[0], allUser1 = allUser[1] };

    return Json(v, JsonRequestBehavior.AllowGet);
} 

我越来越

System.ArgumentOutOfRangeException异常

在

allUser[i] = db.SEATPLAN.Where(d => d.layout_id == lid).ToList();