Author: Tomas Rutkauskas

I'm writing a TStringGrid descendant in which I would like to know, if the ColCount 
is being changed, because I have some other objects hidden in the component, that 
should be updated, when the ColCount changes. How can I accomplish that?

Answer:

You can try the following:

1   unit MyStringGrid;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, Grids;
7   
8   type
9     TMyStringGrid = class(TStringGrid)
10    private
11      FColCount: Integer;
12      FOnColCountChanged: TNotifyEvent;
13      procedure SetColCount(Value: Integer);
14    protected
15      procedure ColCountChanged; virtual;
16    public
17      constructor Create(aOwner: TComponent); override;
18    published
19      property ColCount: Integer read FColCount write SetColCount default 5;
20      property OnColCountChanged: TNotifyEvent read FOnColCountChanged
21        write FOnColCountChanged;
22    end;
23  
24  procedure register;
25  
26  implementation
27  
28  procedure register;
29  begin
30    RegisterComponents('Test', [TMyStringGrid]);
31  end;
32  
33  constructor TMyStringGrid.Create(aOwner: TComponent);
34  begin
35    inherited Create(aOwner);
36    FColCount := 5;
37  end;
38  
39  procedure TMyStringGrid.SetColCount(Value: Integer);
40  begin
41    if FColCount <> Value then
42    begin
43      FColCount := Value;
44      inherited ColCount := FColCount;
45      ColCountChanged;
46    end;
47  end;
48  
49  procedure TMyStringGrid.ColCountChanged;
50  begin
51  
52    {do dependend stuff here}
53  
54    if Assigned(FOnColCountChanged) then
55      FOnColCountChanged(Self);
56  end;
57  
58  end.