Why the widget btn1 in the subpage of QStackedWidget can only define signals for QStackedWidget, but not for page: deviceTypeSelect in QStackedWidget?

Question

I want to use btn1 to send a signal to the slot function of deviceTypeSelect, but btn1 can only be associated with QStackedWidget.

The custom slot method in deviceTypeSelect, I will promote deviceTypeSelect. — Alex, Dec 03 '20 at 08:14
You are going to do it but you haven't, that's why you can't find that slot in Qt Designer. Please provide a [mre] — eyllanesc, Dec 03 '20 at 08:18
Only the predefined slots of *existing* classes can be used. Qt Designer cannot know what slots are going to be in a widget that **will** be promoted, how could it?! — musicamante, Dec 03 '20 at 08:19
I did promoted and the result is still the same.This demo is not easy to describe with code, but pictures are better. — Alex, Dec 03 '20 at 08:27
@Alex: the slots are defined in the python class that is going to be used as the promoted widget, right? — musicamante, Dec 03 '20 at 08:35
The key is why the subpage of QStackedWidget can't accept signal? — Alex, Dec 03 '20 at 08:36

score 1 · Accepted Answer · answered Dec 03 '20 at 09:00

There are two problems.

The first is conceptual: Designer cannot know anything about custom slots that are going to be implemented in a promoted widget, and it even should not. The connection to those slots can only be achieved programmatically, and that's for good reasons: Designer cannot "inspect" (nor it should) the source of the files that will be promoted, and it's also completely possible that one would promote a widget and use different classes with the same design files.

The other problem is technical: the "pages" of multipage widgets like QStackedWidget or QTabWidget cannot be used as signal targets on Designer. I don't know if it's just a missing feature or it's by design (knowing how multipage widget plugins are dealt with I wouldn't bet about the it), but unfortunately it really is not possible.
If you want to connect to standard QWidget slots (setEnabled() etc.), set a dummy boxed layout on the page, and add another QWidget in it, but if you use custom slots, as explained before, those must be manually connected from your code.

Thanks for comment ,So I can only promote QStackedWidget, and then customize the slot in it to associate the signal of btn1. — Alex, Dec 03 '20 at 09:22
That's up to you, but since custom slots can only be connected programmatically there's no much difference, it just depends on what that slot is going to do: if it does something on *that page* only, promoting the page will suffice, but if its interaction is in the common scope of the stacked widget, promote that one instead. — musicamante, Dec 03 '20 at 09:32

Why the widget btn1 in the subpage of QStackedWidget can only define signals for QStackedWidget, but not for page: deviceTypeSelect in QStackedWidget?

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