选择带有变量的对象属性？

Question

我正在使用返回此 JSON 的 API：

"Deadlines": {
        "Monday": "10:00:00",
        "Tuesday": "10:00:00",
        "Wednesday": "10:00:00",
        "Thursday": "10:00:00",
        "Friday": "10:00:00",
        "Saturday": null,
        "Sunday": null
    },

现在我可以使用点表示法获得截止时间。

var deadline = _api.Select(x => x.Deadlines.Friday);

但是，我想要的是检查今天是哪一天

var todaysDayOfWeek = DateTime.Now.DayOfWeek.ToString();

然后将该变量用作属性名称。

但是，我完全不知道该怎么做。我虽然也许我可以使用括号表示法，但我只是得到一个“无法将 [] 索引应用于截止日期类型的表达式。（截止日期只是一个具有周一至周日时间跨度属性的模型）

var todaysDayOfWeek = DateTime.Now.DayOfWeek.ToString();
var deadline = _api.Select(x => x.Deadlines[todaysDayOfWeek]); // <-- produces aforementioned error

    public class Deadlines
    {
        public TimeSpan? Monday { get; set; }
        public TimeSpan? Tuesday { get; set; }
        public TimeSpan? Wednesday { get; set; }
        public TimeSpan? Thursday { get; set; }
        public TimeSpan? Friday { get; set; }
        public TimeSpan? Saturday { get; set; }
        public TimeSpan? Sunday { get; set; }
    }

如何实现这一目标？

Answer 1

好吧，也许您应该使用 Dictionary<DayOfWeek, TimeSpan?> 而不是多个属性。

如果不可能：

高效的方式，switch：

public class Deadlines
{
    public TimeSpan? Monday { get; set; }
    public TimeSpan? Tuesday { get; set; }
    public TimeSpan? Wednesday { get; set; }
    public TimeSpan? Thursday { get; set; }
    public TimeSpan? Friday { get; set; }
    public TimeSpan? Saturday { get; set; }
    public TimeSpan? Sunday { get; set; }
    
    public TimeSpan? GetDeadLine(DayOfWeek dow)
    {
        switch(dow)
        {
            case DayOfWeek.Monday:
                return Monday;
            case DayOfWeek.Tuesday:
                return Tuesday;
            case DayOfWeek.Wednesday:
                return Wednesday;
            case DayOfWeek.Thursday:
                return Thursday;
            case DayOfWeek.Friday:
                return Friday;
            case DayOfWeek.Saturday:
                return Saturday;
            case DayOfWeek.Sunday:
                return Sunday;
            default: throw new ArgumentException(nameof(dow));
        }
    }
}

---

或者你可以有一个返回截止日期的字典：

public class Deadlines
{
    public TimeSpan? Monday { get; set; }
    public TimeSpan? Tuesday { get; set; }
    public TimeSpan? Wednesday { get; set; }
    public TimeSpan? Thursday { get; set; }
    public TimeSpan? Friday { get; set; }
    public TimeSpan? Saturday { get; set; }
    public TimeSpan? Sunday { get; set; }

    private static readonly Dictionary<DayOfWeek, Func<Deadlines, System.TimeSpan?>> DayOfWeekMapper;
    static Deadlines()
    {
        DayOfWeekMapper = new Dictionary<System.DayOfWeek, Func<Deadlines, System.TimeSpan?>>
        {
            { DayOfWeek.Monday, dl => dl.Monday },{ DayOfWeek.Tuesday, dl => dl.Tuesday },{ DayOfWeek.Wednesday, dl => dl.Wednesday },
            { DayOfWeek.Thursday, dl => dl.Thursday },{ DayOfWeek.Friday, dl => dl.Friday },{ DayOfWeek.Saturday, dl => dl.Saturday },{ DayOfWeek.Sunday, dl => dl.Sunday }
        };
    }

    public TimeSpan? GetDeadline(DayOfWeek dow) => DayOfWeekMapper[dow].Invoke(this);
}

---

还有反射，但我不会在这里使用它，因为它效率不高且不可读。

嗯，就是这样：

public class Deadlines
{
    public TimeSpan? Monday { get; set; }
    public TimeSpan? Tuesday { get; set; }
    public TimeSpan? Wednesday { get; set; }
    public TimeSpan? Thursday { get; set; }
    public TimeSpan? Friday { get; set; }
    public TimeSpan? Saturday { get; set; }
    public TimeSpan? Sunday { get; set; }

    private static readonly Dictionary<string,PropertyInfo> DayOfWeekPropertyMapper;
    static Deadlines()
    {
        DayOfWeekPropertyMapper = typeof(Deadlines).GetProperties(BindingFlags.Public | BindingFlags.Instance)
            .Where(p => Enum.GetNames(typeof(DayOfWeek)).Contains(p.Name))
            .ToDictionary(p => p.Name, p => p);
    }

    public TimeSpan? GetDeadline(string dayOfWeek) => (TimeSpan?)DayOfWeekPropertyMapper[dayOfWeek].GetValue(this);
}

使用您的样品：

string dow = DateTime.Now.DayOfWeek.ToString(); 
IEnumerable<TimeSpan?> deadlines = _api.Select(x => x.Deadlines.GetDeadline(dow));

Answer 2

你有两个选择：

• switch语句

  switch( dayOfWeek )
  {
      case Monday: return deadlines.Monday;
      case Tuesday: return deadlines.Tuesday;
      ...
  }
  

• 反射。

  这是相当高级的，而且非常hacky，所以我不推荐它。它包括从typeof(DayOfWeek) 获取字段列表，并为每个字段检查该字段的名称是否是您要查找的名称，如果是，则获取该字段的值。我只是为了完整性而提及它，我不建议使用它，因此我将跳过有关如何使用它的确切细节。