private void button1_Click(object sender, EventArgs e)
 {
     // 将以前的文本变为黑色
     this.richTextBox1.SelectAll();
     this.richTextBox1.SelectionColor = Color.Black;

     int begin = this.richTextBox1.Text.Length - 1;
     if (begin < 0) begin = 0;

     // 添加的文本内容
     string addToRichtextbox = "add @ " + DateTime.Now.ToString("yyyyMMddHHmmss.fff");
     this.richTextBox1.Text += addToRichtextbox + Environment.NewLine;

     int end = this.richTextBox1.Text.Length - 1;
     this.richTextBox1.Select(begin, end - begin+1);
     // 将新加入的文本变为红色
     this.richTextBox1.SelectionColor = Color.Red;
 }