[Development] QDialog vs QPushButton and it's autoDefault default

[Volker Hilsheimer]

> On 11 Feb 2019, at 22:47, Bernhard Lindner <private at bernhard-lindner.de> wrote:
> 
> Hi!
> 
> I just experienced same strange behavior of QPushButton. I want to kindly ask for some
> explanations.
> 
> I wrote a QDialog derived dialog. That dialog has a standard QDialogButtonBox with
> "Accept" and "Close" buttons. It also has various other widgets, especially a table view
> for item selection and a more complex generic/reusable filter panel (QWidget derived) that
> can be attached to any table view for complex user side filtering. That panel contains
> various widgets, including two buttons.
> 
> I now have tripped painfully over a strange behavior that I could track back to the fact
> that one of those two buttons was automagically set as the dialog's default button. Now,
> whenever a user presses <Enter> to confirm QLineEdit filter input, also the mentioned
> clear button is activated - causing a fabulous mess.
> 
> After some research I could explain that unexpected behavior:
> 
> autoDefault : bool
>   This property holds whether the push button is an auto default button.
>   ...
>   This property's default is true for buttons that have a QDialog parent
> 
> This also means there is a workaround: I need to call "setAutoDefault(false)" on each
> button that has the slightest chance to be ever used in a dialog. Everywhere. That is
> doable but seems very counterintuitive to me.
> 
> So my questions are:
> 1. Is this actually how the autoDefault mechanism should work?
> 2. Why an opt-out instead of an opt-in?
> 3. Regarding opt-out: Why not restricting the autoDefault default of true to buttons with
> QDialogButtonBox parents instead of QDialog parents?
> 4. Anyway, is it good style to change the default value (!) of a property dynamically like
> this?



Hey Bernhard,

The default button gets pressed when the user presses Enter in a dialog, unless an autoDefault button has focus, in which case that button will be pressed. That’s what the user would expect.

So, that your button is pressed when focus is in a QLineEdit would suggest that your clear button is the next autoDefault button in the focus chain (as per the documented behavior, and that there is no default button. Note that when using QDialogButtonBox, you only get a default button if one of the buttons in the box has the “Accept” role - otherwise you have to make one of the buttons the default button explicitly.

So to your questions:

1) the behavior you are seeing seems to be as it should be, but you might have to set a default button for autoDefault heuristics not to take over completely and cause confusion.
2) Opt-out would make it more work to have the kind of UI the user expects (focused button is pressed on Enter).
3) QDialogButtonBox isn’t visible to the user, so a button behavior differnelty in a dialog just because it’s laid out in code with the help of QDialogButtonBox seems somewhat arbitrary.
4) Default values of object properties being context dependent is not that unusual


Cheers,
Volker