[Qgis-user] Check if a selectionChanged signal is connected to any slot?

[Tudorache, Marian]

Hi Mathias,

Yeah, this is what I knew in theory. Unfortunately this is not the case.
You can try in python console.
Make sure you have a layer with some features.
Define function executeAfterSelection where you do some dummy printing.
Call three times layer.selectionChanged.connect(executeAfterSelection).
Then try to select features in the layer.
You will see the function executeAfterSelection is execute three times after each selection.

I have done an workaround by introducing a flag variable which tells me if the myLayer.selectionChanged.connect(executeAfterSelection) statement was already called.

Thanks,
Marian

From: Qgis-user [mailto:qgis-user-bounces at lists.osgeo.org] On Behalf Of Matthias Kuhn
Sent: October-03-17 3:13 AM
To: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Check if a selectionChanged signal is connected to any slot?


Hi Marian,

Just tell Qt that it shouldn't create the connection more than once using Qt::UniqueConnection.

Cheers

Matthias

On 10/2/17 5:30 PM, Tudorache, Marian wrote:

Hi everyone,

I have connected the signal selectionChanged so some code, which is executed after features are selected.

myLayer.selectionChanged.connect(self.executeAfterSelection)

Then I have a method self. executeAfterSelection(self, featuresIds)

The SIGNAl/SLOT tandem works but now I realized every time when I call myLayer.selectionChanged.connect(self.executeAfterSelection)  It does not overwrite my previous call. It creates a second signa/slot tandem. During running the method  executeAfterSelection is excuted twice, three times etc.

How can I check if the SIGNAL selectionChanged is connected to the slot executeAfterSelection before I run myLayer.selectionChanged.connect(self.executeAfterSelection)?

I tried this:
receiversCount = QtCore.QObject.receivers(QtCore.SIGNAL("selectionChanged()")
receiversCount = QtCore.QObject.receivers(QtCore.SIGNAL("selectionChanged")
receiversCount = QtCore.QObject.receivers(QtCore.SIGNAL("myLayer.selectionChanged()")
receiversCount = QtCore.QObject.receivers(QtCore.SIGNAL("myLayer.selectionChanged")

Every time I get this error:

QObject.receivers(SIGNAL()): first argument of unbound method must have type 'QObject').


Thanks,
Marian




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