如何允许用户在其选择的位置拖动动态创建的控件

private Control activeControl;
private Point previousLocation;

private void button1_Click(object sender, EventArgs e)
{
    var textbox = new TextBox();
    textbox.Location = new Point(50, 50);
    textbox.MouseDown += new MouseEventHandler(textbox_MouseDown);
    textbox.MouseMove += new MouseEventHandler(textbox_MouseMove);
    textbox.MouseUp += new MouseEventHandler(textbox_MouseUp);

    this.Controls.Add(textbox);
}

void textbox_MouseDown(object sender, MouseEventArgs e)
{
    activeControl = sender as Control;
    previousLocation = e.Location;
    Cursor = Cursors.Hand;
}

void textbox_MouseMove(object sender, MouseEventArgs e)
{
    if (activeControl == null || activeControl != sender)
        return;

    var location = activeControl.Location;
    location.Offset(e.Location.X - previousLocation.X, e.Location.Y - previousLocation.Y);
    activeControl.Location = location;
}

void textbox_MouseUp(object sender, MouseEventArgs e)
{
    activeControl = null;
    Cursor = Cursors.Default;
}

DoDragDrop DragDrop

WM_NCHITTEST DrawToBitmap

  private void button1_Click(object sender, EventArgs e)
    {   Point p = new Point(20,70 * i);
        RichTextBox tb = new RichTextBox();
        tb.Location = p;
        tb.Height= 60;
        tb.Width = 100;
        tb.Font = Normal;
        ControlExtension.Draggable(tb,true);
        this.Controls.Add(tb);
        i++;

https://www.nuget.org/packages/Control.Draggable/