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var
Size : longint;
begin
AStream.Read(Size,SizeOf(Size));
setlength(FText,Size);
AStream.Read(FText[1],Size);
end;

procedure TStringValueClass.SaveToStream(AStream: TFileStream);
var
Size : longint;
begin
Size := length(FText);
AStream.Write(Size,SizeOf(Size));
AStream.Write(FText[1],Size);					

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function LoadStringFromStream(AStream: TStream): String;
var
  ResultString: AnsiString;
  StringSize: Integer;
begin
  Result := '';
  if AStream.Size - AStream.Position < SizeOf(StringSize) then
    Exit;
  AStream.ReadBuffer(StringSize, SizeOf(StringSize));
  SetLength(ResultString, StringSize);
  if AStream.Size - AStream.Position < StringSize then
    Exit;
  AStream.ReadBuffer(Pointer(ResultString)^, StringSize);
  {$ifdef UNICODE} // ab Delphi 2009
  Result := Utf8ToString(ResultString);
  {$else}
  Result := Utf8Decode(ResultString);
  {$endif}
end;

procedure SaveStringToStream(AStream: TStream; AString: String);
var
  StringSize: Integer;
  StringToSave: AnsiString;
begin
  StringToSave := Utf8Encode(AString);
  StringSize := Length(StringToSave);
  AStream.WriteBuffer(StringSize, SizeOf(StringSize));
  AStream.WriteBuffer(Pointer(StringToSave)^, StringSize);
end;

// ...

procedure TStringValueClass.LoadFromStream(AStream: TFileStream);
begin
  FText := LoadStringFromStream(AStream);
end;

procedure TStringValueClass.SaveToStream(AStream: TFileStream);
begin
  SaveStringToStream(AStream, FText);
end;