Form frm = new Form();
frm.MdiParent = this;
frm.Show(); 

//using System.Runtime.InteropServices;

[DllImport("user32.dll")]
public static extern bool ReleaseCapture();
[DllImport("user32.dll")]
public static extern bool SendMessage(IntPtr hwnd, int wMsg, int wParam, int lParam);

//常量
public const int WM_SYSCOMMAND = 0x0112;
//窗体移动
public const int SC_MOVE = 0xF010;
public const int HTCAPTION = 0x0002;
//改变窗体大小
public const int WMSZ_LEFT = 0xF001;
public const int WMSZ_RIGHT = 0xF002;
public const int WMSZ_TOP = 0xF003;
public const int WMSZ_TOPLEFT = 0xF004;
public const int WMSZ_TOPRIGHT = 0xF005;
public const int WMSZ_BOTTOM = 0xF006;
public const int WMSZ_BOTTOMLEFT = 0xF007;
public const int WMSZ_BOTTOMRIGHT = 0xF008;

public void MouseDownMove(object sender, MouseEventArgs e)
{
    ReleaseCapture();
    SendMessage(this.Handle, WM_SYSCOMMAND, SC_MOVE + HTCAPTION, 0);
}

public frmMain()
{
    InitializeComponent();
    this.MouseDown += MouseDownMove;
    //this.ListBox.MouseDown += MouseDownMove;
}

// 设置光标位置 到文本最后
this.tbTestDialogue.Focus();
this.tbTestDialogue.SelectionStart = this.tbTestDialogue.TextLength;
//this.tbTestDialogue.SelectionLength = this.tbTestDialogue.TextLength;
// 随文本滚动 
this.tbTestDialogue.ScrollToCaret(); 

public void AddToMyListBox()
{
        listBox1.BeginUpdate();
        for(intx=1;x<5000;x++)
        {
                listBox1.Items.Add("Item"+x.ToString());
        }
        listBox1.EndUpdate(); 
}

//打开文件对话框
private void openFileDialogBtn_Click(object sender, EventArgs e) 
{
             OpenFileDialog opd = new OpenFileDialog();           
             opd.InitialDirectory = @"D:\"; //对话框初始路径
             opd.Filter = "C#文件(*.cs)|*.cs|文本文件(*.txt)|*.txt|所有文件(*.*)|*.*"; 
             opd.FilterIndex = 2;  //默认就选择在文本文件(*.txt)过滤条件
             opd.DereferenceLinks = false;  //返回快捷方式的路径而不是快捷方式映射的文件的路径   
             opd.Title = "打开对话框";   
             opd.RestoreDirectory = true;  //每次打开都回到InitialDirectory设置的初始路径     
             opd.ShowHelp = true; //对话框多了个"帮助"按钮   
             opd.ShowReadOnly = true; //对话框多了"只读打开"的复选框   
             opd.ReadOnlyChecked = true; //默认"只读打开"复选框勾选   
             // opd.HelpRequest +=new EventHandler(opd_HelpRequest); //注册帮助按钮的事件
             // opd.FileOk += new CancelEventHandler(opd_FileOk);  //效果等同于下面
             if(opd.ShowDialog() == DialogResult.OK)
             { 
                  string filePath = opd.FileName;   //文件路径
                  string fileName = opd.SafeFileName;  //文件名 
             } 
}      

private void opd_FileOk(object sender, CancelEventArgs e) 
{ 
              //do something  
}     

/// <summary> 
/// 帮助按钮单击事件 
/// </summary> 
/// <param name="sender"></param> 
/// <param name="e"></param> 
private void opd_HelpRequest(object sender, EventArgs e) 
{ 
              MessageBox.Show("这是帮助说明");    
} 

//保存文件对话框
private void saveFileDialogBtn_Click(object sender, EventArgs e)
{
　　　　　　  SaveFileDialog sfd = new SaveFileDialog();
            sfd.InitialDirectory = @"D:\"; //对话框初始路径 
            sfd.FileName = "config.txt"; //默认保存的文件名 
            sfd.Filter = "C#文件(*.cs)|*.cs|文本文件(*.txt)|*.txt|所有文件(*.*)|*.*";
            sfd.FilterIndex = 2;  //默认就选择在文本文件(*.txt)过滤条件上 
            sfd.DefaultExt = ".xml";  //默认保存类型，如果过滤条件选"所有文件(*.*)"且保存名没写后缀，则补充上该默认值 
            sfd.DereferenceLinks = false;  //返回快捷方式的路径而不是快捷方式映射的文件的路径 
            sfd.Title = "保存对话框";
            sfd.RestoreDirectory = true;  //每次打开都回到InitialDirectory设置的初始路径 
            sfd.ShowHelp = true; //对话框多了个"帮助"按钮 
            // sfd.HelpRequest += new EventHandler(sfd_HelpRequest); //注册帮助按钮的事件
            // sfd.FileOk += new CancelEventHandler(sfd_FileOk);  //效果等同于下面
            if (sfd.ShowDialog() == DialogResult.OK） 
            {
                string filePath = sfd.FileName;   //文件路径 
            }
}

private void sfd_FileOk(object sender, CancelEventArgs e)
{
            //do something   
}

/// <summary> 
/// 帮助按钮单击事件 
/// </summary> 
/// <param name="sender"></param> 
/// <param name="e"></param> 
private void sfd_HelpRequest(object sender, EventArgs e)
{
            MessageBox.Show("这是帮助说明");
}

//打开文件夹对话框
private void folderBrowserDialogBtn_Click(object sender, EventArgs e)  
{  
              FolderBrowserDialog fbd = new FolderBrowserDialog();  
              fbd.RootFolder = Environment.SpecialFolder.Desktop;  //设置默认根目录是桌面 
              fbd.Description = "请选择文件目录:";   //设置对话框说明    
              if (fbd.ShowDialog() == DialogResult.OK)  
              {  
                  string filePath = fbd.SelectedPath;    
              }  
}