使用DefineProperties替换TPersistent属性,例如TFont

Question

我正在更新组件中的一些属性.为了避免遗漏属性错误,我使用DefineProperties从流中读取旧属性.大多数属性工作正常,例如Integer,但我无法获得基于TPersistent的属性来工作.在读属性(TPersistent)在程序踏浪号是受保护的,不公开的,需要一个黑客来访问它.即使这样,也永远不会调用ReadFontProperty过程,并且会发生缺失的属性异常.

我如何阅读TFont属性？

这是我试图做的一些示例代码.

...

type
  TMyComponent = class(TComponent)
  strict private
    // Removed 
    //FIntegerProperty: Integer;
    //FFontProperty: TFont;

    // New
    FNewIntegerProperty: Integer;
    FNewFontProperty: TFont;

    procedure ReadIntegerProperty(Reader: TReader);
    procedure ReadFontProperty(Reader: TReader);
  protected
    procedure DefineProperties(Filer: TFiler); override;
  published
    // Removed properties
    //property IntegerProperty: Integer read FIntegerProperty write FIntegerProperty;
    //property FontProperty: TFont read FFontProperty write SetFontProperty;

    // New properties
    property NewIntegerProperty: Integer read FNewIntegerProperty write FNewIntegerProperty;
    property NewFontProperty: TFont read FNewFontProperty write SetNewFontProperty;
  end;

implementation

procedure TMyComponent.DefineProperties(Filer: TFiler);
begin
  inherited;

  // This works
  Filer.DefineProperty('IntegerProperty', ReadIntegerProperty, nil, FALSE);

  // This doesn't
  Filer.DefineProperty('FontProperty', ReadFontProperty, nil, FALSE);
end;

procedure TMyComponent.ReadIntegerProperty(Reader: TReader);
begin
  FNewIntegerProperty:= Reader.ReadInteger;
end;

type
  THackReader = class(TReader);

procedure TMyComponent.ReadFontProperty(Reader: TReader);
begin
  { TODO : This doesn't work. How do we read fonts? }
  THackReader(Reader).ReadProperty(FNewFontProperty);
end;

...

更新1

使用以下代码尝试了David的建议:

Filer.DefineProperty('Font.CharSet', ReadFontCharSet, nil, False);

...

procedure TMyComponent.ReadFontCharSet(Reader: TReader);
begin
  Reader.ReadInteger;
end;

我收到无效的属性值错误.我想这与Charset属于TFontCharset类型(= System.UITypes.TFontCharset = 0..255)有关.我如何阅读这种类型的财产？

Answer 1

为此，您需要使用的每个单独发布的属性，TFont并且需要使用完全限定的名称。

Filer.DefineProperty('FontProperty.Name', ReadFontName, nil, False);
Filer.DefineProperty('FontProperty.Height', ReadFontHeight, nil, False);
Filer.DefineProperty('FontProperty.Size', ReadFontSize, nil, False);
// and so on for all the other published properties of TFont

ReadFontName，ReadFontHeight等应读取旧的属性值到新命名的组件。

procedure TMyComponent.ReadFontName(Reader: TReader);
begin
  FNewFontProperty.Name := Reader.ReadString;
end;

// etc. etc.

更新资料

您询问如何读取Charset属性。这很复杂，因为它既可以写为文本标识符（请参见FontCharsetsGraphics.pas中的常量），也可以写为纯整数值。这是一些快速被黑客入侵的代码，它们将读取您的Charset。

procedure TMyComponent.ReadFontCharset(Reader: TReader);

  function ReadIdent: string;
  var
    L: Byte;
    LResult: AnsiString;
  begin
    Reader.Read(L, SizeOf(Byte));
    SetString(LResult, PAnsiChar(nil), L);
    Reader.Read(LResult[1], L);
    Result := UTF8ToString(LResult);
  end;

  function ReadInt8: Shortint;
  begin
    Reader.Read(Result, SizeOf(Result));
  end;

  function ReadInt16: Smallint;
  begin
    Reader.Read(Result, SizeOf(Result));
  end;

var
  Ident: string;
  CharsetOrdinal: Integer;

begin
  Beep;
  case Reader.ReadValue of
  vaIdent:
    begin
      Ident := ReadIdent;
      if not IdentToCharset(Ident, CharsetOrdinal) then begin
        raise EReadError.Create('Could not read MyFont.Charset');
      end;
      FNewFontProperty.Charset := CharsetOrdinal;
    end;
  vaInt8:
    FNewFontProperty.Charset := ReadInt8;
  vaInt16:
    FNewFontProperty.Charset := ReadInt16;
  else
    raise EReadError.Create('Could not read FontProperty.Charset');
  end;
end;