TComponent，TControl，TWinControl，TGraphic的DefineProperties赏析与说明（不懂）

先观赏一下最后的实现效果：

object Form1: TForm1
  Left =
  Top =
  Width =
  Height =
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -
  Font.Name = 'MS Shell Dlg 2'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch =
  TextHeight =
  object Image1: TImage
    Left =
    Top =
    Width =
    Height =
    Picture.Data = {
      0A544A504547496D616765784A0000FFD8FFE000104A46494600010100000100
      010000FFFE003B43524541544F523A2067642D6A7065672076312E3020287573
      696E6720494A47204A50454720763632292C207175616C697479203D2035350A
      FFDB0043000E0A0B0D0B090E0D0C0D100F0E11162417161414162C20211A2434
      2E3736332E32323A4153463A3D4E3E32324862494E56585D5E5D3845666D655A
      6C535B5D59FFDB0043010F10101613162A17172A593B323B5959595959595959
      A790060033A74F4EB4EFEDBD1F83FDA761C74FF484E3F5AF11A427934728F94F
      6B5D5743495A55BFD35646FBCE26404FD4E69C359D195D9C6A5A7ABBE37113A6
      4E3A679AF123C527B51617297B5B9125D775192370E8F73232B29C86058E0834
      550A29947FFFD9}
  end
  object Panel1: TPanel
    Left =
    Top =
    Width =
    Height =
    Caption = 'Panel1'
    TabOrder =
  end
  object Button1: TButton
    Left =
    Top =
    Width =
    Height =
    Caption = 'Button1'
    TabOrder =
    OnClick = Button1Click
  end
  object Button2: TButton
    Left =
    Top =
    Width =
    Height =
    Caption = 'Button2'
    TabOrder =
    OnClick = Button2Click
  end
  object Timer1: TTimer
    OnTimer = Timer1Timer
    Left =
    Top =
  end
end

VCL的实现代码：

procedure TComponent.DefineProperties(Filer: TFiler);
var
  Ancestor: TComponent;
  Info: Longint;
begin
  Info := ;
  Ancestor := TComponent(Filer.Ancestor);
  if Ancestor <> nil then Info := Ancestor.FDesignInfo;
  Filer.DefineProperty('Left', ReadLeft, WriteLeft,
    LongRec(FDesignInfo).Lo <> LongRec(Info).Lo);
  Filer.DefineProperty('Top', ReadTop, WriteTop,
    LongRec(FDesignInfo).Hi <> LongRec(Info).Hi);
end;

存储Left与Top的值。另外Height和Width是在哪里存储的？

procedure TControl.DefineProperties(Filer: TFiler);

  function DoWriteIsControl: Boolean;
  begin
    if Filer.Ancestor <> nil then
      Result := TControl(Filer.Ancestor).IsControl <> IsControl else
      Result := IsControl;
  end;
begin
  { The call to inherited DefinedProperties is omitted since the Left and
    Top special properties are redefined with real properties }
  Filer.DefineProperty('IsControl', ReadIsControl, WriteIsControl, DoWriteIsControl);
end;

存储IsControl的值，但是我怎么没见到？

procedure TWinControl.DefineProperties(Filer: TFiler);

  function PointsEqual(const P1, P2: TPoint): Boolean;
  begin
    Result := ((P1.X = P2.X) and (P1.Y = P2.Y));
  end;

  function DoWriteDesignSize: Boolean;
  var
    I: Integer;
  begin
    Result := True;
    if (Filer.Ancestor = nil) or not PointsEqual(FDesignSize,
      TWinControl(Filer.Ancestor).FDesignSize) then
    begin
      if FControls <> nil then
        for I := 0 to FControls.Count - 1 do
          with TControl(FControls[I]) do
            if (Align = alNone) and (Anchors <> [akLeft, akTop]) then
              Exit;
      if FWinControls <> nil then
        for I := 0 to FWinControls.Count - 1 do
          with TControl(FWinControls[I]) do
            if (Align = alNone) and (Anchors <> [akLeft, akTop]) then
              Exit;
    end;
    Result := False;
  end;

begin
  inherited;
  Filer.DefineProperty('DesignSize', ReadDesignSize, WriteDesignSize,
    DoWriteDesignSize);
end;

存储DesignSize的值

procedure TCustomForm.DefineProperties(Filer: TFiler);
begin
  inherited DefineProperties(Filer);
  Filer.DefineProperty('PixelsPerInch', nil, WritePixelsPerInch, not IsControl);
  Filer.DefineProperty('TextHeight', ReadTextHeight, WriteTextHeight, not IsControl);
  Filer.DefineProperty('IgnoreFontProperty', ReadIgnoreFontProperty, nil, False);
end;

写入三个值，但是我怎么没见到？

procedure TGraphic.DefineProperties(Filer: TFiler);

  function DoWrite: Boolean;
  begin
    if Filer.Ancestor <> nil then
      Result := not (Filer.Ancestor is TGraphic) or
        not Equals(TGraphic(Filer.Ancestor))
    else
      Result := not Empty;
  end;

begin
  Filer.DefineBinaryProperty('Data', ReadData, WriteData, DoWrite);
end;

写入Data的二进制数据

// TPicture直接继承于TInterfacedPersistent，与TGraphic相互独立
procedure TPicture.DefineProperties(Filer: TFiler); 

  function DoWrite: Boolean;
  var
    Ancestor: TPicture;
  begin
    if Filer.Ancestor <> nil then
    begin
      Result := True;
      if Filer.Ancestor is TPicture then
      begin
        Ancestor := TPicture(Filer.Ancestor);
        Result := not ((Graphic = Ancestor.Graphic) or
          ((Graphic <> nil) and (Ancestor.Graphic <> nil) and
          Graphic.Equals(Ancestor.Graphic)));
      end;
    end
    else Result := Graphic <> nil;
  end;

begin
  Filer.DefineBinaryProperty('Data', ReadData, WriteData, DoWrite);
end;

写入Data的二进制数据

---------------------------------------------------------------------------

其中TControl的IsControl使用方法如下：

constructor TControl.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FWindowProc := WndProc;
  FControlStyle := [csCaptureMouse, csClickEvents, csSetCaption, csDoubleClicks];
  FFont := TFont.Create;
  FFont.OnChange := FontChanged;
  FAnchors := [akLeft, akTop];
  FConstraints := TSizeConstraints.Create(Self);
  FConstraints.OnChange := DoConstraintsChange;
  FColor := clWindow;
  FVisible := True;
  FEnabled := True;
  FParentFont := True;
  FParentColor := True;
  FParentShowHint := True;
  FParentBiDiMode := True;
  FIsControl := False;
  FDragCursor := crDrag;
  FFloatingDockSiteClass := TCustomDockForm;
  FHelpType := htContext;
end;

procedure TControl.ReadIsControl(Reader: TReader);
begin
  FIsControl := Reader.ReadBoolean;
end;

procedure TControl.WriteIsControl(Writer: TWriter);
begin
  Writer.WriteBoolean(FIsControl);
end;

测试代码：

procedure TForm1.Button1Click(Sender: TObject);
begin
    if Image1.IsControl then
        ShowMessage('Image1 is control')
    else
        ShowMessage('Image1 is not control'); // 走这里

    if Button2.IsControl then
        ShowMessage('Button2 is control')
    else
        ShowMessage('Button2 is not control'); // 走这里
end;

继续：