Hide X button (close) at message box in Inno Setup

Question

How to hide X button at message box?

I want to see this, if is possible:

Answer 1

I do not think this is possible.

One possible workaround is to implement the message box from the scratch.

And remove the biSystemMenu from the TForm.BorderIcons (or actually setting it empty).

procedure MyMessageBoxWithoutCloseButton;
var
  Form: TSetupForm;
  Button: TNewButton;
  MesssageLabel: TLabel;
begin
  Form := CreateCustomForm;
  Form.BorderStyle := bsDialog;
  Form.Position := poOwnerFormCenter;
  Form.ClientWidth := ScaleX(400);
  Form.ClientHeight := ScaleY(130);
  Form.BorderIcons := []; { No close button }
  Form.Caption := 'Caption';

  MesssageLabel := TLabel.Create(Form);
  MesssageLabel.Parent := Form;
  MesssageLabel.Left := ScaleX(16);
  MesssageLabel.Top := ScaleX(16);
  MesssageLabel.Width := Form.ClientWidth - 2*ScaleX(16);
  MesssageLabel.Height := ScaleY(32);
  MesssageLabel.AutoSize := False;
  MesssageLabel.WordWrap := True;
  MesssageLabel.Caption := 'Lorem ipsum dolor sit amet, ...';

  Button := TNewButton.Create(Form);
  Button.Parent := Form;
  Button.Width := ScaleX(80);
  Button.Height := ScaleY(24);
  Button.Left := Form.ClientWidth - Button.Width - ScaleX(8);
  Button.Top := Form.ClientHeight - Button.Height - ScaleY(8);
  Button.Caption := 'Accept';
  Button.ModalResult := mrOK;

  Form.ShowModal;
end;

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Note that it's still possible to close the message box using Alt-F4.

To prevent that handle OnCloseQuery. For an example, see How to Delete / Hide / Disable [OK] button on message box.