Show feature count with PyQGIS 3

Question

After adding a layer to my QGIS project with a Python script, I want to show the number of objects beside the layer in the layer window.

I have tried this code, which is from

Show feature count of layer via Python console / PyQGIS

to see if it works in QGIS 3.

## create the memory layer and add to the registry
myLayer = QgsVectorLayer("Point", "myLayer", "memory")
QgsMapLayerRegistry.instance().addMapLayer(myLayer, False)

## reference to the layer tree
root = QgsProject.instance().layerTreeRoot()

## adds the memory layer to the layer node at index 0
myLayerNode = QgsLayerTreeLayer(myLayer)
root.insertChildNode(0, myLayerNode)

## set custom property
myLayerNode.setCustomProperty("showFeatureCount", True)

The module QgsMapLayerRegistry seems to have changed from QGIS 2 to QGIS 3, because when I enter >>>help(QgsMapLayerRegistry), I am getting this error message:

help(QgsMapLayerRegistry)
Traceback (most recent call last):
  File "C:\PROGRA~1\QGIS3~1.4\apps\Python37\lib\code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
NameError: name 'QgsMapLayerRegistry' is not defined

I also tried to use the method showFeatureCount() on my freshly created layer, but that didn't work either.

mem_layer = QgsVectorLayer(uri, 'my_file', 'delimitedtext')
        QgsProject.instance().addMapLayer(mem_layer)
        mem_layer.loadNamedStyle(r"P:\my_style.qml")
        mem_layer.showFeatureCount()
        mem_layer.triggerRepaint()

What do I need to change to make the code work?

Answer 1

In QGIS 3, QgsMapLayerRegistry() has been replaced by QgsProject(). You can find more information about backwards compatibility here.

To show the feature count of a newly-added layer, you could use something like the following:

mem_layer = QgsVectorLayer(uri, 'my_file', 'delimitedtext')
QgsProject.instance().addMapLayer(mem_layer)
mem_layer.loadNamedStyle(r"P:\my_style.qml")
mem_layer.triggerRepaint()

# Show Feature Count
root = QgsProject.instance().layerTreeRoot()
myLayerNode = root.findLayer(mem_layer.id())
myLayerNode.setCustomProperty("showFeatureCount", True)