c# - 查找谓词 DayOfWeek Issue c#

Question

最近我遇到了一个问题，当我试图在 DayOfWeek 的列表中找到特定的一天时，它在星期日效果不佳，但在其他所有日子都有效。

我做了一个谓词，但是当我在一个空列表或一个不包含星期日的列表中寻找星期日时，它找到了它。

例子:

namespace testing1
{
    public partial class Timer : Form
    {
        public static List<dayOfWeek> day = new List<dayOfWeek>();//I can set things in it

        public Timer()
        {
            InitializeComponent();
        }

        private void Timer_Load(object sender, EventArgs e)
        {
                Console.WriteLine(day.Count); //return 0 when I instantiate the form without inserting from an another form.

                checkBox1.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Monday; }) == dayOfWeek.Monday; // return false OK
                checkBox2.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Tuesday; }) == dayOfWeek.Tuesday; // return false OK
                checkBox3.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Wednesday; }) == dayOfWeek.Wednesday; // return false OK
                checkBox4.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Thursday; }) == dayOfWeek.Thursday; // return false OK
                checkBox5.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Friday; }) == dayOfWeek.Friday; // return false OK
                checkBox6.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Saturday; }) == dayOfWeek.Saturday; // return false OK
                checkBox7.Checked = day.Find((dayOfWeek d) => { return d == dayOfWeek.Sunday; }) == dayOfWeek.Sunday; // return true WTF ????
        }
    }
}

需要我帮忙吗？

Answer 1

DayOfWeek是一个 enum因此它是值类型，值类型变量不能有空值，除非标记为Nullable<> ，这意味着很可能是 DayOfWeek 中的第一个值enum是 Sunday 这将是默认值，所以无论何时 Find无法找到该值，它在本例中返回默认值 星期日。

您应该改用 Contains :

day.Contains(DayOfWeek.Sunday);
//..