Author: Tomas Rutkauskas

What I am trying to achieve is to let many different objects attach to a single 
event. I did it with Interfaces but I want to do it with normal methods now. My 
first attempt was to simply store a pointer in a TList, but of course it did not 
work. I did not think about the Code and Data pointers. My question: How do I store 
methods in a list in a generic way? I do not want to specify the event type in my 
base class, only in my specialized classes.

Answer:

The problem is that a TNotifyEvent is more than a pointer: it includes both data 
and class information. In any case, here is a solution for you. Drop two buttons on 
a form, and link the Unit1 code in below.


1   unit Unit1;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, Contnrs,
7       StdCtrls;
8   
9   type
10    TNotifyEventObj = class
11    private
12      FNotifyEvent: TNotifyEvent;
13    public
14      constructor Create(aNE: TNotifyEvent);
15      property NotifyEvent: TNotifyEvent read FNotifyEvent write FNotifyEvent;
16    end;
17  
18    TForm1 = class(TForm)
19      Button1: TButton;
20      Button2: TButton;
21      procedure Button1Click(Sender: TObject);
22      procedure Button2Click(Sender: TObject);
23    private
24      { Private declarations }
25      FList: TObjectList;
26      FCount: integer;
27      procedure CountEvent(Sender: TObject);
28    public
29      { Public declarations }
30      constructor Create(AOwner: TComponent); override;
31      destructor Destroy; override;
32      procedure AddEvent(aNE: TNotifyEvent);
33  
34    end;
35  
36  var
37    Form1: TForm1;
38  
39  implementation
40  
41  {$R *.DFM}
42  
43  { TNotifyEventObj }
44  
45  constructor TNotifyEventObj.Create(aNE: TNotifyEvent);
46  begin
47    FNotifyEvent := aNE;
48  end;
49  
50  { TForm1 }
51  
52  constructor TForm1.Create(AOwner: TComponent);
53  begin
54    inherited;
55    FCount := 0;
56    FLIst := TObjectList.Create;
57  end;
58  
59  destructor TForm1.Destroy;
60  begin
61    FList.Free;
62    inherited;
63  end;
64  
65  procedure TForm1.Button1Click(Sender: TObject);
66  begin
67    AddEvent(CountEvent);
68  end;
69  
70  procedure TForm1.Button2Click(Sender: TObject);
71  var
72    lNE: TNotifyEvent;
73    I: Integer;
74  begin
75    for I := 0 to FList.Count - 1 do { Iterate }
76    begin
77      lNE := TNotifyEventObj(FList[I]).NotifyEvent;
78      lNE(self);
79    end;
80  end;
81  
82  procedure TForm1.AddEvent(aNE: TNotifyEvent);
83  begin
84    FLIst.Add(TNotifyEventObj.Create(aNE));
85  end;
86  
87  procedure TForm1.CountEvent(Sender: TObject);
88  begin
89    FCount := FCount + 1;
90    Caption := IntToStr(FCount);
91  end;
92  
93  end.