50 signal/slots
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Hello. What will run faster, 50 signals connected to their own slot, or 1 signal reused 50 times with 1 slot? I prefer the first option because it is a lot less redundant code writing for me. I setup the 50 signals to emit their object name as a QString and call findChild on it to update the text on a label in the slot (it's for a hardware status page). As I understand it, an emit signal is just like calling the slot function directly.
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it's equal, one signal emitted means one function call. the count of slots connected to one signal (or conversely) has no impact on performance
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Hi @servant-0 , I think your scenario in practice will be the same as each signal contains a look up to its connected slot.
So each emit is only connected to one slot - i.e: each emit only iterates its own connection list (one slot).
The other way round is 50 signals each with their own slot incurs exactly the same per-signal overhead - i.e: one slot per emit. -
Awesome! Thank you so much @ankou29666 and @Ben-Campbell-Wallis. I will avoid redundant code and use the dynamic 1 slot/signal approach then.
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S servant 0 has marked this topic as solved
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Hello. What will run faster, 50 signals connected to their own slot, or 1 signal reused 50 times with 1 slot? I prefer the first option because it is a lot less redundant code writing for me. I setup the 50 signals to emit their object name as a QString and call findChild on it to update the text on a label in the slot (it's for a hardware status page). As I understand it, an emit signal is just like calling the slot function directly.
Usually both variants should be about the same time. You would have to benchmark it.
That said:
@servant-0 said in 50 signal/slots:I setup the 50 signals to emit their object name as a QString and call findChild on it to update the text on a label in the slot
findChild is incredibly slow, depending on your UI magnitudes slower than other parts of your code. I would recommend using it as little as possible and not regularly in slots
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Hello. What will run faster, 50 signals connected to their own slot, or 1 signal reused 50 times with 1 slot? I prefer the first option because it is a lot less redundant code writing for me. I setup the 50 signals to emit their object name as a QString and call findChild on it to update the text on a label in the slot (it's for a hardware status page). As I understand it, an emit signal is just like calling the slot function directly.
@servant-0 said in 50 signal/slots:
I setup the 50 signals to emit their object name as a QString and call findChild on it to update the text on a label in the slot
All as @J.Hilk has written about
findChild(). Also it depends hugely on whether your target widget is "close" in the hierarchy to the widget you callfindChild()on. If that is "high up" it has a lot of searching to do if there are a lot of descendent widgets.It sounds like you have a backend data layer which emits a signal when it changes and passes the value of what will be used as a widget's
objectName()to indicate which widget to update? If so that is not ideal for decoupling data from UI.You might like to look at QDataWidgetMapper for a means of tying widgets to data values (works in both directions, though you may only need data->widget direction). For that you would store your data values in anything derived from a
QAbstractItemModeland any time that data changes internally a signal is sent and the corresponding widget is updated (without lookup).
