QQ聊天窗口效果

rtbDetail:显示聊天信息

rtbChat:用户输入信息

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsFormsApplication4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        [DllImport("user32.dll")]
        private static extern int SendMessage(IntPtr hWnd,int msg,int wParam,IntPtr IParam);
        private const int WM_VSCROLL = 0x115;
        private const int SB_BOTTOM = 7;
        private int lastSelectedIndex = -1;

        private void btnSend_Click(object sender, EventArgs e)
        {
            rtbDetail.Text += rtbChat.Text+Environment.NewLine;
            rtbChat.Text = "";
            SendMessage(rtbDetail.Handle,WM_VSCROLL,SB_BOTTOM,new IntPtr(0));
            rtbChat.Focus();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            rtbChat.Focus();
            this.AcceptButton = btnSend;
        }
    }
}