Creating a TStringGrid class in delphi where the object array associated with the cells is specified as a more specific type

1
votes

In Delphi, how can I create a class derived from the TStringGrid class such that the TObject array associated with the grids cells is of a more specific type for example TColor which would be used to specify the colour of the cell?

2
delphiinheritancetstringgrid
You might want to observe -- given the wording "a more specific type" -- that the Delphi TColor type isn't a class and so doesn't belong to any class hierarchy. A TColor isn't a TObject. It so happens, however, that a TColor is a 32-bit integer and therefore fits into a TObject (=pointer) variable on all platforms used today (32 bit and 64 bit). TButton, TBitmap, and TStringList are classes, however, so a TStringList instance is a TObject. – Andreas Rejbrand

2 Answers

6
votes
type
  TStringColorGrid = class(TStringGrid)
  private
    function GetColor(ACol, ARow: Integer): TColor;
    procedure SetColor(ACol, ARow: Integer; AValue: TColor);
  public
    property Colors[ACol, ARow: Integer]: TColor read GetColor write SetColor;
  end;

function TStringColorGrid.GetColor(ACol, ARow: Integer): TColor;
begin
  Result := TColor(inherited Objects[ACol, ARow]);
end;

procedure TStringColorGrid.SetColor(ACol, ARow: Integer; AValue: TColor);
begin
  inherited Objects[ACol, ARow] := TObject(AValue);
end;
2
votes

TStringGrid can hold a TObject for each cell. TColor doesn't inherit from TObject so it doesn't work.

You could cast a TColor to a TObject but this would be a bad solution prone to future issues. And this would not work for any type (Only those having at most the size of a pointer).

The best solution is to "box" your data into a TObject and save the instance of such an object into the StringGrid.

TMyBoxingColorObject = class
    Data : TColor;           // Or any other datatype
end;

Don't forget to create and free the object as needed!

You can also use generics if you have a lot of different types to box.