Catching signal when rule toggles (active/inactive) using PyQGIS?

Question

I would like to catch a signal when a rule within a rule based layer toggles visibility. How to permanently check this

layer.renderer().rootRule().children()[0].active()==True

the same way we can receive a signal when a node in the layer tree toggles visibility:

layer= iface.layerTreeView().currentNode()
layer.visibilityChanged.connect(dosomething)

The problem is I cannot catch the visibility change on a rule.

To add more context:

The layer "SM_GIS pds_electricity < 10000" is a copy of "PDS Electricité <2000" but with other scale ranges.

(I will hide it for the user but that's not the question here).

What I want: if I set the rule "Prosumer" to visible in one layer , I want it to be set to visible in the same rule of the other layer.

A workaround is to make copies of the same layer and use single symbol and applying each rule to a new copy of the layer.

Answer 1

The signal you are searching is QgsMapLayer.styleChanged.

And here a code below. I use partial to give as parameter the layer who has the rule checked/unchecked, this is for the case you connect multiple layers to the updateRules function.

• activeRules function create a dictionnary with label rules as keys and checkstate as values.
• updateRules function change rule visibility for all other mapLayers if the rule name is found.

from functools import partial

def activeRules(vectorLayer):
    vlar = dict()
    rend = vectorLayer.renderer()
    for lsi in rend.legendSymbolItems():
        chked = rend.legendSymbolItemChecked(lsi.ruleKey())
        vlar[lsi.label()] = (Qt.Unchecked, Qt.Checked)[chked]
    return vlar

def updateRules(vectorLayer):
    vlrules = activeRules(vectorLayer)
    # from https://gis.stackexchange.com/a/261240/93097
    for ml in QgsProject.instance().mapLayers().values():
        mlid = ml.id()
        renderer  = ml.renderer()
        if renderer.type() == 'RuleRenderer':
            if mlid != vectorLayer.id():
                ltl = QgsProject.instance().layerTreeRoot().findLayer(mlid)
                ltm = iface.layerTreeView().model()
                legendNodes = ltm.layerLegendNodes(ltl)
                for ln in legendNodes:
                    nodname = ln.data(0)
                    if nodname in vlrules:
                        ln.setData(vlrules[nodname], Qt.CheckStateRole)

main_vl = QgsProject.instance().mapLayersByName("PDS Electricité")[0]
main_vl.styleChanged.connect(partial(updateRules, main_vl))