How to make close button open a new form on Delphi-CodePudding

I need that "x" button on any form would not close the form but instead open another 3 random forms on delphi, i have no idea how to do that, please help

CodePudding user response：

Just use the form's OnCloseQuery event to detect the user's trying to close your form (by clicking the close button in the top-right corner, by double-clicking the form's title bar icon, by selecting the Close system menu item, by pressing Alt F4, etc.).

Then set CanClose to False and instead open your three new forms:

procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
  CanClose := False;
  Form2.Show;
  Form3.Show;
  Form4.Show;
end;

CodePudding user response：

As suggested by @AndreasRejbrand's answer, you could use the Form's OnCloseQuery event. But, the problem with that approach is that the event is also triggered during system reboot/shutdown, and you don't want to block that. If OnCloseQuery returns CanClose=False during a system shutdown, the shutdown is canceled.

Another option is to use the Form's OnClose event instead, setting its Action parameter to caNone, eg:

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caNone;
  Form2.Show;
  Form3.Show;
  Form4.Show;
end;

However, the best option would to be to handle only user-initiated closures (the X button, ALT-F4, etc) by having the Form handle the WM_SYSCOMMAND message looking for SC_CLOSE notifications, eg:

procedure TForm1.WndProc(var Message: TMessage);
begin
  if (Message.Msg = WM_SYSCOMMAND) and (Message.WParam and $FFF0 = SC_CLOSE) then
  begin
    Message.Result := 0;
    Form2.Show;
    Form3.Show;
    Form4.Show;
  end
  else
    inherited;
end;

This way, system-initiated closures are unhindered.