Debug Qt signals, slots and connections

Question

Is there a way to see which signals are fired, and if there is a slot connected to them? Ideally, we'd like to see all signals, not just those of a particular class or method; e.g. QSignalSpy only allows us to track specific signals of specific instances.

In our application, we've seen performance problems because of a signal being emitted twice from different components. In the end, it turned out that there was a second instance of a class that should have only been there once. Knowing which signals are emitted exactly helps in debugging this.

Signals are called via QMetaObject::invoke*, I was hoping to find something there to hook into, but I found nothing obvious.

possible duplicate of How to intercept ALL signals emitted by a given event in QT? — exilit
If you want to have just one instance of the class, why didn't you use the singleton pattern to control number of objects? — Afshin

James Turner James Turner · Accepted Answer · 2016-06-08T10:39:10

(disclaimer, I work for KDAB) : KDAB's GammaRay tool can show you objects and connections at runtime, without requiring any source changes. It inspects the meta-object tables and does some code-injection hooks to make this work.

Debug Qt signals, slots and connections

2 Answers