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Panel component which resizes children

This simple descendent of a TPanel component resizes children controls at DESIGN time.  It works OK, except it has a bug where if you close the project, then reopen the project, THEN resize one of the stretchPanels, the children controls of that panel resize themselves wildly.  After that, it works ok.  It also works ok if you drop a 'stretchPanel' component on a form from scratch and drop some controls inside it.
I need to know what is going wrong and why!

Here is the component source:

unit aPanel1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls;

type
  TPanelStretch = class(TPanel)
  private
    { Private declarations }
    nOldWidth, nOldHeight: integer;

  protected
    { Protected declarations }
    procedure Resize; override;
  public
    { Public declarations }
    constructor create(AOwner : TComponent); override;
//    procedure Resize(const Value: TNotifyEvent); override;
  published
    { Published declarations }
//    property OnResize: TNotifyEvent read aaResize write aaResize; override;
//    property OnResize; override;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('Samples', [TPanelStretch]);
end;

{ TPanel1 }

constructor TPanelStretch.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  if ( csDesigning in ComponentState ) then
    begin
      nOldWidth := Width;
      nOldHeight := Height;
    end
  else
    begin
      nOldWidth := -1;
      nOldHeight := -1;
    end;
end;

procedure TPanelStretch.Resize;
var
  i:     Integer;
  ratio: Double;
  ctl:   TWinControl;
begin
  inherited;
  if ( nOldWidth = -1 ) and ( nOldHeight = -1 ) then
  begin
    nOldWidth := Width;
    nOldHeight := Height;
    exit;
  end;
  ratio := Width / nOldWidth;
  for i := 0 to ControlCount - 1 do
    begin
      ctl := TWinControl( Controls[i] );
      ctl.Left := Round( ctl.Left * ratio );
      ctl.Width := Round( ctl.Width * ratio );
    end;
  ratio := Height / nOldHeight;
  for i := 0 to ControlCount - 1 do
    begin
      ctl := TWinControl( Controls[i] );
      ctl.Top := Round( ctl.Top * ratio );
      ctl.Height := Round( ctl.Height * ratio );
    end;
  nOldWidth := Width;
  nOldHeight := Height;
end;

end.
0
abulka
Asked:
abulka
  • 2
  • 2
  • 2
1 Solution
 
rwilson032697Commented:
I think the problem is that the TPanelStretch constructor is setting the Old width and height to be the default width and height of TPanel. After this happens the properties of the panel and its children are read in. Then when you resize the old width and height are not the right values.

You need to override the Loaded method (which is called after the properties are read in etc) and set the old widht and height in that method).

Cheers,

Raymond.
0
 
viktornetCommented:
Do you think it might have to do with the -1 you set for the Width and Height???

Maybe when the project is loaded the OldWidth and Height are set to 0 or something and then when you resize it it resizes wildly :)

Cheers,
Viktor
0
 
abulkaAuthor Commented:
Sounds good.  Can you give me a template line or two of code for overriding the Loaded method?

Viz. When I overrode the resize method, I was faced with options to override e.g. the resize property and possibly the resize notification events? and I got lost inside the VCL source code trying to find the right thing to override (and and syntax)
0
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viktornetCommented:
procedure Loaded;override;

procedure TPanelStretch.Loaded;
begin
  Inherited;
  OldWidth := Width;
  OldHeight := Height;
end;

Cheers,
Viktor
0
 
rwilson032697Commented:
Viktor has done it nicely...

Cheers,

Raymond.
0
 
abulkaAuthor Commented:
Thanks.  Here is the finished component.  Pretty clean and simple.

unit aPanel1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls;

type
  TPanelStretch = class(TPanel)
  private
    { Private declarations }
    nOldWidth, nOldHeight: integer;

  protected
    { Protected declarations }
    procedure Resize; override;
    procedure Loaded; override;
  public
    { Public declarations }
    constructor create(AOwner : TComponent); override;
  published
    { Published declarations }
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('Samples', [TPanelStretch]);
end;

{ TPanel1 }

constructor TPanelStretch.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  nOldWidth := Width;
  nOldHeight := Height;
end;

procedure TPanelStretch.Loaded;
begin
  inherited;
  nOldWidth := Width;
  nOldHeight := Height;
end;

procedure TPanelStretch.Resize;
var
  i:     Integer;
  ratio: Double;
  ctl:   TWinControl;
begin
  inherited;

  ratio := Width / nOldWidth;
  for i := 0 to ControlCount - 1 do
    begin
      ctl := TWinControl( Controls[i] );
      ctl.Left := Round( ctl.Left * ratio );
      ctl.Width := Round( ctl.Width * ratio );
    end;
  ratio := Height / nOldHeight;
  for i := 0 to ControlCount - 1 do
    begin
      ctl := TWinControl( Controls[i] );
      ctl.Top := Round( ctl.Top * ratio );
      ctl.Height := Round( ctl.Height * ratio );
    end;
  nOldWidth := Width;
  nOldHeight := Height;
end;

end.

0

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