c#中WinForm的TextBox循环自动滚动示例

这个问题来自论坛提问，演示代码如下

using  System;
using  System.Collections.Generic;
using  System.ComponentModel;
using  System.Data;
using  System.Drawing;
using  System.Text;
using  System.Windows.Forms;
using  System.Runtime.InteropServices;
namespace  WindowsApplication27
... {
     /**/ ///   <summary>
     ///  演示如何在TextBox中让文字循环滚动:
     ///  作者jinjazz
     ///  作者blog: http://blog.csdn.net/jinjazz
     ///   </summary>
     public   partial   class  Form1 : Form
     ... {
         public  Form1()
         ... {
            InitializeComponent();

             this .textBox1.Clear();
             for  ( int  i  =   0 ; i  <=   20 ;i ++  )
             ... {
                 this .textBox1.Text  +=   string .Format( " {0}:jinjazz__{1} " , i,i);
            }
             this .timer1.Interval  =   200 ;
             this .timer1.Start();
        }

         // 发送消息
        [DllImport( " user32.dll " , EntryPoint  =   " SendMessage " )]
         public   static   extern   int  SendMessage(IntPtr hWnd,  int  wMsg,  int  wParam,  int  lParam);
         // 获取滚动条位置
        [DllImport( " user32 " )]
         public   static   extern   int  GetScrollPos(IntPtr hwnd,  int  nBar);
         // 设置滚动条位置
        [DllImport( " user32.dll " )]
         static   extern   int  SetScrollPos(IntPtr hWnd,  int  nBar,
                                        int  nPos,  bool  bRedraw);

         public   const   int  EM_LINESCROLL  =   0xb6 ;
 
         private   void  timer1_Tick( object  sender, EventArgs e)
         ... {
             int  i =   GetScrollPos( this .textBox1.Handle, 1 );

             // 向下滚动一行
            SendMessage( this .textBox1.Handle, EM_LINESCROLL,  0 ,  1 ); // 0，1代表垂直滚动条向下滚动

             // 判断是否有位置变化，如果没有则说明到了底部，返回开始处
             if  (i  ==  GetScrollPos( this .textBox1.Handle,  1 ))
             ... {
                 // 回到顶部，这里用SetScrollPos似乎有问题，滚动条和文字不是同步更新
                 this .textBox1.SelectionStart  =   0 ;
                 this .textBox1.SelectionLength  =   1 ;
                 this .textBox1.ScrollToCaret();
                 this .textBox1.SelectionLength  =   0 ;
            }
            Console.WriteLine(i);
        }

         private   void  textBox1_MouseEnter( object  sender, EventArgs e)
         ... {
             this .timer1.Stop();
        }

         private   void  textBox1_MouseLeave( object  sender, EventArgs e)
         ... {
             this .timer1.Start();
        }
    }
}