c#上一周下一周代码

public partial class Form1 : Form
    {
        DateTime dtNow;
        public Form1()
        {
            InitializeComponent();


        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
            label1.Text = DateTime.Now.ToString("yyyy-MM-dd");
            dtNow = DateTime.Now;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            showDays(false);//上一周
        }

        private void button2_Click(object sender, EventArgs e)
        {
            showDays(true);//下一周
        }

        void showDays(bool isNext)
        {
            textBox1.Text = "";
            int k = isNext ? 1 : -1;
            DateTime d1 = dtNow.AddDays(k * 7);
            while (d1.DayOfWeek != DayOfWeek.Sunday)
            {
                d1 = d1.AddDays(k);
            }
            for (int i = 0; i < 7; i++)
            {
                textBox1.AppendText(d1.AddDays(i+1).ToString("yyyy-MM-dd") + Environment.NewLine);
            }
            dtNow = d1;//起始日期
        }
    }