pyqgis – Preserving QgsLayerTreeViewIndicator When Moving Node in Layer Tree

Question

I am using the script below to display an icon next to my layer in the layer tree view, which works fine. However, when a user moves the position of that node, the indicator disappears.

layer1 = QgsVectorLayer("Point?crs=EPSG:4326", "my layer", "memory")
QgsProject.instance().addMapLayer(layer1, False)

root = QgsProject.instance().layerTreeRoot()
node_layer1 = root.addLayer(layer1)

indicator = QgsLayerTreeViewIndicator(iface.layerTreeView())
indicator.setToolTip('Test')
indicator.setIcon(QIcon(':/images/themes/default/mActionIdentify.svg'))
indicator.clicked.connect(lambda: print('indicator clicked'))

iface.layerTreeView().addIndicator(node_layer1, indicator)

How would I preserve the indicator and the connected action, so that it can be triggered even after moving the node?

Some context on what I additionally tried so far:

I tried to listen for the QAbstractItemModel.rowsMoved signal, to identify when the node is moved and then again re-add the indicator afterwards.

But it seems that only this specific signal is not emitted by QgsLayerTreeModel.

Another thing I tried is listening to the rowsInserted signals to detect if my created node has been inserted at a different position, in order to then again re-add the indicator. But that also does not work, because on moving the node the original object gets deleted. So if I try to add the indicator with iface.layerTreeView().addIndicator(node_layer1, indicator) it complains about a

RuntimeError: wrapped C/C++ object of type QgsLayerTreeLayer has been
deleted

Answer 1

I was able to get it working with the code below:

layer1 = QgsVectorLayer("Point?crs=EPSG:4326", "my layer", "memory")
QgsProject.instance().addMapLayer(layer1, False)

root = QgsProject.instance().layerTreeRoot()
node = root.addLayer(layer1)

indicator = QgsLayerTreeViewIndicator(iface.layerTreeView())
indicator.setToolTip('Test')
indicator.setIcon(QIcon(':/images/themes/default/mActionIdentify.svg'))
indicator.clicked.connect(lambda: print('indicator clicked'))

view = iface.layerTreeView()

view.addIndicator(node, indicator)

def rows_inserted(parent, first, last):
    nodes = root.findLayers()
    for n in nodes:
        if n.layer().id() == layer1.id():
            if not view.indicators(n):
                view.addIndicator(n, indicator)

conn = view.layerTreeModel().rowsInserted.connect(rows_inserted)

After removing layer, clean up by disconnecting signal/slot and deleting indicator object:

QObject.disconnect(conn)
del indicator

Screencast shows this working:

Based very loosely on source code in qgslayertreeviewindicatorprovider.cpp which would probably take care of this nicely but does not seem to be exposed in the Python API bindings.