How to create a panel which resizes itself and all components on it at runtime

Problem/Question/Abstract:

How to create a panel which resizes itself and all components on it at runtime

Answer:

Here's the source code for a resizable panel. Give the panel an align property of alClient, throw some controls on it, and watch them resize at run time when you resize the form. There is some code that prohibits resizing during design time, but this can be taken out.

unit Elastic;

interface

uses
  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls, Forms, Dialogs, ExtCtrls;

type
  TElasticPanel = class(TPanel)
  private
    FHorz, FVert: boolean;
    nOldWidth, nOldHeight: integer;
    bResized: boolean;
  protected
    procedure WMSize(var message: TWMSize); message WM_SIZE;
  public
    nCount: integer;
    constructor Create(AOwner: TComponent); override;
  published
    property ElasticHorizontal: boolean read FHorz write FHorz default True;
    property ElasticVertical: boolean read FVert write FVert default True;
  end;

procedure Register;

implementation

constructor TElasticPanel.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FHorz := True;
  FVert := True;
  nOldWidth := Width;
  nOldHeight := Height;
  bResized := False;
end;

procedure TElasticPanel.WMSize(var message: TWMSize);
var
  bResize: boolean;
  xRatio: real;
  i: integer;
  ctl: TWinControl;
begin
  Inc(nCount);
  if Align = alNone then
    bResize := TRUE
  else
    bResize := bResized;
  if not (csDesigning in ComponentState) and bResize then
  begin
    if FHorz then
    begin
      xRatio := Width / nOldWidth;
      for i := 0 to ControlCount - 1 do
      begin
        ctl := TWinControl(Controls[i]);
        ctl.Left := Round(ctl.Left * xRatio);
        ctl.Width := Round(ctl.Width * xRatio);
      end;
    end;
    if FVert then
    begin
      xRatio := Height / nOldHeight;
      for i := 0 to ControlCount - 1 do
      begin
        ctl := TWinControl(Controls[i]);
        ctl.Top := Round(ctl.Top * xRatio);
        ctl.Height := Round(ctl.Height * xRatio);
      end;
    end;
  end
  else
  begin
    nOldWidth := Width;
    nOldHeight := Height;
  end;
  bResized := TRUE;
  nOldWidth := Width;
  nOldHeight := Height;
end;

procedure Register;
begin
  RegisterComponents('Additional', [TElasticPanel]);
end;

end.