Author: Tomas Rutkauskas

By hooking into the WndProc I can listen to the messages generated for 
TWinControls. I am looking for the WN_CUT, WM_PASTE and WM_CLEAR so that I can lock 
a record before the cut, paste or clear change occurs. The TComboBox does not 
generate these events when the Style is csDropDown. Any way to capture these events?

Answer:

Override the ComboWndProc method ín a class derived from TCombobox. Example:

1   unit Unit1;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
7     Dialogs, StdCtrls;
8   
9   type
10    TCombobox = class(stdctrls.TComboBox)
11    protected
12      procedure ComboWndProc(var message: TMessage; ComboWnd: HWnd;
13        ComboProc: Pointer); override;
14    end;
15    TForm1 = class(TForm)
16      ComboBox1: TComboBox;
17      Memo1: TMemo;
18    private
19      { Private declarations }
20    public
21      { Public declarations }
22    end;
23  
24  var
25    Form1: TForm1;
26  
27  implementation
28  
29  {$R *.dfm}
30  
31  { TCombobox }
32  
33  procedure Report(const S: string);
34  begin
35    form1.memo1.lines.add(S);
36  end;
37  
38  procedure TCombobox.ComboWndProc(var message: TMessage; ComboWnd: HWnd;
39    ComboProc: Pointer);
40  begin
41    inherited;
42    case message.Msg of
43      WM_CUT: Report('CUT');
44      WM_PASTE: Report('PASTE');
45      WM_CLEAR: Report('CLEAR');
46    end;
47  end;
48  
49  end.