Question

为什么无法添加对象列表“ListOfMachines”即将出现空引用：

SFC.Terminal.dll中发生了'System.NullReferenceException'类型的异常，但未在用户代码中处理。

模型“MachineModel”：

public class MachineModel
    {
        public List<MachinesModelForList> ListOfMachines { get; set; }
        public int QtyOfWorkerActivities { get; set; }
    }

模型“MachinesModelForList”：

public class MachinesModelForList  
{
    public int ID;
    public string Name { get; set; }
    public string Description { get; set; }
    public string UserName { get; set; }
    public string OrderId { get; set; }
    public string Index { get; set; }
    public int Operation { get; set; }
    public byte Shift { get; set; }
    public int Status { get; set; }
    public string StatusColor { get; set; }
    public string StatusName { get; set; }
    public int UserId { get; set; }
    public int Slots { get; set; }
    public DateTime? EndDate {get; set;}
    public int MachineActivity { get; set;}
}

功能：

  public MachineModel LoggedWorkerActivity()
    {
        var userloggeduserID = HttpContext.Current.User.Identity.GetUserId();
        var DB = new TerminalDBContext();

        var workerListOfMachinesID = DB.MachineActivity.Where(p => p.UserID.ToString() == userloggeduserID & p.EndDate == null).Select(p => p.MachineID).ToList();

        var machineModel = new MachineModel();
        foreach (int i in workerListOfMachinesID)
        {
            var ob = DB.Machine.Where(p => p.ID == i)

                .Select(m => new MachinesModelForList
                {
                    Status = DB.MachineActivity.Where(x => x.MachineID == m.ID).Select(p => p.StatusReason.Status.ID).FirstOrDefault(),
                    Description = m.Description,
                    Name = m.Name,
                    Slots = m.Slots,
                    ID = DB.MachineActivity.Where(x => x.MachineID == m.ID).Select(p => p.MachineID).FirstOrDefault(),
                    UserId = DB.MachineActivity.Where(x => x.MachineID == m.ID).Select(p => p.UserID).FirstOrDefault(),
                    EndDate = DB.MachineActivity.Where(x => x.MachineID == m.ID).Select(p => p.EndDate).FirstOrDefault(),
                    MachineActivity = DB.MachineActivity.Where(p => p.MachineID == m.ID & p.EndDate == null).Count()
                }).FirstOrDefault();

            machineModel.ListOfMachines.Add(ob);
            machineModel.QtyOfWorkerActivities++;

        }

        return machineModel;
    }

Answer 1

只需创建列表实例

machineModel.ListOfMachines = new List<MachinesModelForList>();
machineModel.ListOfMachines.Add(ob);

无法将对象添加到列表中

1 个答案: