Expanding or collapsing layer groups with PyQGIS 3

Question

PyQGIS 2 has a function to expand/collapse a layers with a subset of styles in the Layers panel as follows:

self.iface.legendInterface().setLayerExpanded(self.segments_layer, False)

I know that in PyQGIS 3 self.iface.legendInterface() has been replaced by gsProject.instance().layerTreeRoot() but making that switch in this case produces an error:

AttributeError: 'QgsLayerTree' object has no attribute 'setLayerExpanded'

What is the appropriate replacement for setLayerExpanded in PyQGIS 3?

Answer 1

You can access it from the QgsLayerTreeNode::setExpanded() function:

root = QgsProject.instance().layerTreeRoot()
layer = QgsProject.instance().mapLayersByName('Layer_Name')[0]
myLayerNode = root.findLayer(layer.id())
myLayerNode.setExpanded(True)