mscorlib.dll中发生了类型为'System.InvalidOperationException'的未处理异常

Question

    private void findManagerForSelectedDate(String dateSelected)
    {
        dateSelected = dateTimePicker1.Value.ToShortDateString();

        List<String> managerNames = new List<String>();
        foreach(var item in managers)
        {
            foreach (var subitem in item)
            {
                CalendarModel c = subitem;
                Console.WriteLine(c.date);
                c.name = new CultureInfo("en-US", false).TextInfo.ToTitleCase(c.name);
                if (userSelection.Count > 0)
                {
                    foreach (var addedUser in userSelection)
                    // Crashing here with An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll
                    {
                        if (!addedUser.Contains(c.name))
                        {
                            userSelection.Add(c.name);
                        }
                    }
                } else
                {
                    userSelection.Add(c.name);
                }

它能够遍历我的列表3次，然后在第4次崩溃。

异常详细信息显示{“集合已被修改；枚举操作可能无法执行。”}

Answer 1

您可以将用户添加到临时列表中，然后将此临时列表添加到原始列表的末尾：

    private void findManagerForSelectedDate(String dateSelected)
    {
        dateSelected = dateTimePicker1.Value.ToShortDateString();

        List<string> tempUsersToAdd = new List<string>();
        List<String> managerNames = new List<String>();
        foreach(var item in managers)
        {
            foreach (var subitem in item)
            {
                CalendarModel c = subitem;
                Console.WriteLine(c.date);
                c.name = new CultureInfo("en-US", false).TextInfo.ToTitleCase(c.name);
                if (userSelection.Count > 0)
                {
                    foreach (var addedUser in userSelection)
                    {
                        if (!addedUser.Contains(c.name))
                        {
                            tempUsersToAdd.Add(c.name);
                        }
                    }
                }
                else
                {
                    tempUsersToAdd.Add(c.name);
                }
            }
        }

        userSelection.AddRange(tempUsersToAdd);

Answer 2

使用foreach循环遍历集合时，无法编辑它

骇客就是要遍历您收藏的副本：

foreach (var addedUser in userSelection.ToArray())

并保持相同的代码

Answer 3

您可以使用linq来测试c.name是否在userSelection中

if(!userSelection.Exists( u => u.Contains(c.name))) userSelection.Add(c.name);

当然您需要using System.Linq