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Frequently Asked Questions

Disabling ALT-F4 to prevent form closing

Question:

How can I disable the Alt+F4 key combination to keep my form from closing?

Answer:

If the intent is to make sure the user doesn't exit prematurely
before performing some required task, use the OnCloseQuery event
of the form and set the CanClose property appropriately.

If you need to override the default behavior for normal form 
handling and prevent the Alt+F4 keystrokes from being responded
to, then set the forms KeyPreview property to true and
trap the key during the forms KeyDown event.

Example:

procedure TForm1.FormCreate(Sender: TObject);
begin
  KeyPreview := true;
end;

procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if ((ssAlt in Shift) and (Key = VK_F4)) then
    Key := 0;
end;

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