New expression of "legendInterface()" in qgis3.0?

Question

What is the correct expression of "legendInterface()" in qgis3.0? I tried with "layerTreeNode", but it doesn't work.

root = QgsProject.instance().layerTreeRoot()

for group in [child for child in root.children() if child.nodeType() == 0]:
    if group=="POSTE_DETENTE":
        group_actif = root.findGroup(group)
        #now, I would iterate on layers in the list L in order to get the polygon layers
        for (type, sys, champ, name) in L:
          #get the polygon layer
          if type=='polygon':
            #create_layer is a function that I create previously and return a new layer in memory
            layer=create_layer(type, sys, champ, name):
            # add layer to the legend
            QgsProject.instance().addMapLayer(layer, False)
            # add layer to the group - False to let the choice where to place the layer in the group
            group_actif.addLayer(layer)

Answer 1

I think this is what you're looking for:

root = QgsProject.instance().layerTreeRoot()

for group in [child for child in root.children() if child.nodeType() == 0]:
    if group.name() == 'POSTE_DETENTE':
        …

Node types: NodeGroup - 0, NodeLayer - 1

Please also see help(QgsLayerTreeLayer) for additional reference