The Simplest Drag / Dock

Drag and dock is not very hard in C++ Builder. And it is a very effective way to create a customizable Single Document Interface (SDI).

Before dragging off the form...
After...

All of the work is done by the system with a few property settings and no code.

Here is the form as a Text DFM...

object Form1: TForm1
      Left = 8
      Top = 156
      Width = 337
      Height = 335
      Caption = 'Form1'
      Color = clBtnFace
      DockSite = True
      Font.Charset = DEFAULT_CHARSET
      Font.Color = clWindowText
      Font.Height = -11
      Font.Name = 'MS Sans Serif'
      Font.Style = []
      OldCreateOrder = False
      PixelsPerInch = 96
      TextHeight = 13
      object DraggablePanel: TPanel
            Left = 8
            Top = 8
            Width = 113
            Height = 137
            Caption = 'DraggablePanel'
            Color = clHighlightText
            UseDockManager = False
            DragKind = dkDock
            DragMode = dmAutomatic
            TabOrder = 0
      end
end

That's it - no code, just this on the panel...

      DragKind = dkDock
      DragMode = dmAutomatic

and this...

      DockSite = True

on the form.