c# winform richTextBox 自动显示最后一行

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication11
{
public partial class Form1 : Form
{
private RichTextBox rtxt = null;
private TextBox txt = null;
private Button btn = null;
public Form1()
{
InitializeComponent();
//RichTextBox
rtxt = new RichTextBox();
rtxt.Location = new Point(5, 5);
rtxt.Width = this.Width-30 ;
rtxt.ScrollBars = RichTextBoxScrollBars.Vertical;
this.Controls.Add(rtxt);
//TextBox
txt = new TextBox();
txt.Location=new Point(5,rtxt.Height+5);
this.Controls.Add(txt);
//Button
btn = new Button();
btn.Text = "发送";
btn.Location = new Point(txt.Width + 5, rtxt.Height + 5);
btn.Click += new EventHandler(btn_Click);
this.Controls.Add(btn);
}
/// <summary>
/// 发送信息
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void btn_Click(object sender, EventArgs e)
{
string message = txt.Text.Trim();
rtxt.AppendText(message+"\n");
rtxt.Select(rtxt.Text.Length, 0);
rtxt.ScrollToCaret();
}
}
}