How to free control inside its event handler?

Question

Hi,

Does anybody know the trick, how to free control inside its event handler ? According delphi help it is not possible...

I want to free dynamicaly created TEdit, when Self.Text=''.

TAmountEdit = class (TEdit)
.
.
public
  procedure KeyUp(var Key: Word; Shift :TShiftState);
end;

procedure TAmountEdit.KeyUp(var Key: Word; Shift :TShiftState);
begin
inherited;
if Text='' then Free; // after calling free, an exception arises
end;

How should do to achieve the same effect?

Thanx

Answer 1

Haven't tested it, but it should work:

Edit: Tested, works!
Edit 2: Now using CM_RELEASE instead of custom window message. Kudos to LachlanG!

interface
type
  TAmountEdit = class (TEdit)
    ...
    procedure KeyUp(var Key: Word; Shift :TShiftState); override;
    procedure HandleRelease(var Msg: TMessage); message CM_RELEASE;
    ...
  end;

implementation

procedure TAmountEdit.KeyUp(var Key: Word; Shift :TShiftState);
begin
  inherited;
  if Text = '' then
    PostMessage(Handle, CM_RELEASE, 0, 0);
end;

procedure TAmountEdit.HandleRelease(var Msg: TMessage);
begin
  Free;
end;

Your component should be freed when the message is handled either automatically or when you call Application.ProcessMessages.

Note: Yepp this is kind of a workaround and there might be better solutions out there ;)

Answer 2

Before implementing this I would stop and ask "Is this really the best approach?"

Do you really want an edit control class that always destroys itself when key input results in the Text property becoming an empty string?

Is it not more likely to be the case that you have a specific form/dialog where this behaviour is required? In which case, there is no problem... you can free the edit control in the KeyUp event handled by the form without incurring an Access Violation.