C#保存、清空复选框的值

代码为:

public partial class Form1 : Form
    {
        Dictionary<int, string> dicAnswer = new Dictionary<int, string>();  //答案集合，键为题号，值为答案
        public Form1()
        {
            InitializeComponent();
        }
        /// <summary>
        /// 单击下一题触发事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnbtnAnswerDown_Click(object sender, EventArgs e)
        {
            Save();
            ClearSelected();
        }
        /// <summary>
        /// 保存答案
        /// </summary>
        private void Save() 
        {
            System.Windows.Forms.Control.ControlCollection cons = this.pnlSelectProject.Controls;   //pnlSelectProject为Pannel容器，其中多选项都包含在内
            int AnswerNo = Convert.ToInt32(this.lblNumber.Text);
            string str = string.Empty;
            foreach (Control con in cons)
            {
                CheckBox cbox = con as CheckBox;
                if (cbox.Checked == true)
                {
                    str += cbox.Text + ",";
                }
            }
            if (!string.IsNullOrEmpty(str))
            {
                str = str.Substring(0, str.Length - 1);
                dicAnswer.Add(AnswerNo, str);
                this.lblNumber.Text = (AnswerNo+1).ToString();
            }
            else
            {
                MessageBox.Show("至少选择一个答案！");
            }
        }
        /// <summary>
        /// 清除选中项
        /// </summary>
        private void ClearSelected() 
        {
            System.Windows.Forms.Control.ControlCollection cons = this.pnlSelectProject.Controls;
            foreach (Control con in cons)
            {
                (con as CheckBox).Checked = false;
            }
        }
        /// <summary>
        /// 显示答案
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnShowAnswer_Click(object sender, EventArgs e)
        {
            string answerStr = string.Empty;
            foreach (KeyValuePair<int,string> dic in dicAnswer)
            {
                answerStr += "第" + dic.Key + "题：" + dic.Value+"\n";
            }
            if (!string.IsNullOrEmpty(answerStr))
            {
                MessageBox.Show(answerStr);    
            }
            else
            {
                MessageBox.Show("没有答案！");
            }
            
        }
        
    }