[Interest] Handling signal-slot connections on demand (sanity check request)

Forrest Leeson forrestuuid at gmail.com
Sat Jan 28 01:33:27 CET 2017

Assume an application that creates a focusable dialog with 9 buttons.
Clicking buttons 1-8 causes the creation of new windows — type 1
through type 8, each type supporting a slot, S, that can be connected
to the signal of button 9.

Clicking button 9 should trigger slot S only of the window that was
most recently active. Which is to say the connection can't usefully be
set up when the window is created.

A solution would seem to be to add a look-at-me signal to all the
window types, which they would emit to the dialog upon receiving
focus; the receiver would then [ disconnect(Button9,0,0,0) ] and then
connect Button 9 to the signalling window's slot S by way of
QObject::sender() with a side order of qobject_cast...at which point I
am realize I am stupid and ignorant and have misplaced all my B
vitamins and choline supplements and my coffee is cold and foul.
The documentation warns against using Sender this way, but chides
rather than forbids. Look-at-me signals not arriving in order would be
a dealbreaker, but unless I'm misreading, establishing the connection
with Qt::DirectConnection will fix that. And I guess checking for 0
against the result of the cast will avoid crashing.

So: is this approach even minimally sane, and even if so is there a
(better) way to do it?

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