以下方法调用有什么问题？

Question

可能重复:
.NET中的NullReferenceException是什么？

我有一个名为HoursOfOperation的模型(ASP.NET MVC 4,C#):

public class HoursOfOperation
{
    public List<DayTimes> Monday { get; set; }
    public List<DayTimes> Tuesday { get; set; }
    public List<DayTimes> Wednesday { get; set; }
    public List<DayTimes> Thursday { get; set; }
    public List<DayTimes> Friday { get; set; }
    public List<DayTimes> Saturday { get; set; }
    public List<DayTimes> Sunday { get; set; }
}

和日间时间

public class DayTimes
{
    public int Status { get; set; }
    public string From { get; set; }
    public string To { get; set; }
}

现在我正在尝试向星期一实体添加一个新集,如下所示:

var _vm = new HoursOfOperation();

_vm.Monday.Add(new DayTimes{
      From = day.From.ToString(),
      To = day.To.ToString(),
      Status = (int)day.Status
});

一旦上述陈述被解除,我就会得到一个"Object reference not set to an instance of an object."例外

现在我已经检查并且day.From.ToString()有一个"08:00:00",day.To.ToString()has "09:30:00"和day.Status 1在此语句抛出异常时有一个.

有任何想法吗？

Answer 1

那是因为Monday没有实例化.

你应该做点什么

_vm.Monday = new List<DayTimes>();

或者,在HoursOfOperation构造函数中进行所有实例化,如下所示:

public HoursOfOperation()
{
   Monday = new List<DayTimes>(),
   Tuesday = new List<DayTimes>(),
   Wednesday = new List<DayTimes>(),
   Thursday = new List<DayTimes>(),
   Friday = new List<DayTimes>(),
   Saturday = new List<DayTimes>(),
   Sunday = new List<DayTimes>()
};