TabPageDragDrop

using System;
using System.Drawing;
using System.Windows.Forms;
public class MyToolWindow : Form
{
    public MyToolWindow()
    {
        FormBorderStyle = FormBorderStyle.SizableToolWindow;
    }
}
public class MyTabControl : TabControl
{
    private static MyTabControl DropTarget { get; set; }
    public MyTabControl()
    {
        this.AllowDrop = true;
    }
    Point p1;
    int d = 16;
    protected override void OnMouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);
        p1 = e.Location;
    }
    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);
        if (e.Button == MouseButtons.Left && this.SelectedTab != null)
        {
            var p2 = e.Location;
            if ((p1.X - p2.X) * (p1.X - p2.X) + ((p1.Y - p2.Y)) * (p1.Y - p2.Y) > d * d)
            {
                this.DoDragDrop(this.SelectedTab, DragDropEffects.All);
            }
        }
    }
    protected override void OnDragEnter(DragEventArgs e)
    {
        base.OnDragEnter(e);
        if (e.Data.GetDataPresent(typeof(TabPage)))
        {
            e.Effect = DragDropEffects.Move;
            DropTarget = this;
        }
    }
    protected override void OnDragLeave(EventArgs e)
    {
        base.OnDragLeave(e);
        DropTarget = null;
    }
    protected override void OnDragOver(DragEventArgs e)
    {
        base.OnDragOver(e);
        if (e.Data.GetDataPresent(typeof(TabPage)))
        {
            e.Effect = DragDropEffects.Move;
            DropTarget = this;
        }
    }
    protected override void OnGiveFeedback(GiveFeedbackEventArgs e)
    {
        base.OnGiveFeedback(e);
        if (DropTarget == null)
        {
            e.UseDefaultCursors = false;
            Cursor.Current = Cursors.SizeAll;
        }
    }
    protected override void OnQueryContinueDrag(QueryContinueDragEventArgs e)
    {
        base.OnQueryContinueDrag(e);
        if (e.Action == DragAction.Drop && DropTarget == null)
        {
            var tabPage = this.SelectedTab;
            if (!this.RectangleToScreen(this.Bounds).Contains(Cursor.Position))
            {
                var form = new MyToolWindow();
                form.Text = tabPage.Text;
                var tabControl = new MyTabControl();
                DropTarget = tabControl;
                tabControl.Dock = DockStyle.Fill;
                form.Controls.Add(tabControl);
                form.StartPosition = FormStartPosition.Manual;
                form.Location = new Point(Cursor.Position.X - 16,
                    Cursor.Position.Y - SystemInformation.ToolWindowCaptionHeight - 16);
                form.Show();
                e.Action = DragAction.Continue;
            }
        }
    }
    protected override void OnDragDrop(DragEventArgs e)
    {
        base.OnDragDrop(e);
        if (e.Data.GetDataPresent(typeof(TabPage)))
        {
            var tabPage = (TabPage)e.Data.GetData(typeof(TabPage));
            var f1 = tabPage.FindForm();
            var t1 = tabPage.Parent as MyTabControl;
            this.TabPages.Remove(tabPage);
            this.TabPages.Add(tabPage);
            var f2 = tabPage.FindForm();
            f2.Activate();
            if (f1 is MyToolWindow && f1 != f2 && t1 != null && t1.TabCount == 0)
                f1.Close();
        }
    }
    private const int WM_NCHITTEST = 0x84;
    private const int HTTRANSPARENT = -1;
    private const int HTCLIENT = 1;
    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == WM_NCHITTEST)
        {
            if (m.Result.ToInt32() == HTTRANSPARENT)
                m.Result = new IntPtr(HTCLIENT);
        }
    }
}