How to capture the WM_CUT, WM_CLEAR and WM_PASTE messages in a TComboBox

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How to capture the WM_CUT, WM_CLEAR and WM_PASTE messages in a TComboBox (Views: 719)

Problem/Question/Abstract:

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:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TCombobox = class(stdctrls.TComboBox)
  protected
    procedure ComboWndProc(var Message: TMessage; ComboWnd: HWnd;
      ComboProc: Pointer); override;
  end;
  TForm1 = class(TForm)
    ComboBox1: TComboBox;
    Memo1: TMemo;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TCombobox }

procedure Report(const S: string);
begin
  form1.memo1.lines.add(S);
end;

procedure TCombobox.ComboWndProc(var Message: TMessage; ComboWnd: HWnd;
  ComboProc: Pointer);
begin
  inherited;
  case message.Msg of
    WM_CUT: Report('CUT');
    WM_PASTE: Report('PASTE');
    WM_CLEAR: Report('CLEAR');
  end;
end;

end.

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