集合已修改；可能无法执行枚举操作。

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private List<MyClass> iList = new List<MyClass>();

        private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < 10; i++)
            {
                MyClass c = new MyClass();
                c.IntField = i;
                c.StrField = string.Format("string{0}", i);
                iList.Add(c);
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            //foreach (MyClass c in iList)
            //{
            //    iList.Remove(c);          // 这里会出现问题：集合已修改；可能无法执行枚举操作。
            //}

            // 用For代替
            for (int i = iList.Count - 1; i >= 0; i++)
            {
                MyClass c = iList[i];
                iList.Remove(c);
            }
        }

        class MyClass
        {
            private int _intField;
            public int IntField
            {
                get { return _intField; }
                set { _intField = value; }
            }

            private string _strField;
            public string StrField
            {
                get { return _strField; }
                set { _strField = value; }
            }
        }
    }