PyQGIS – Fix AttributeError When Getting Selected Layers in QGIS

attributeerrorlayerspyqgisselect

How can I get the selected layers in QGIS 3 with PyQGIS?

I tried:

selectedLayers = iface.legendInterface().selectedLayers()

as suggested in Programmatically get selected layers from the QGIS legend?, but it seems that there is an API breaking change

QgsLegendInterface was removed. It was replaced by layer tree API
(QgsLayerTreeNode class and others). Methods that deal with custom
actions in main window's layer tree context menu were moved to
QgisInterface:

I then tried:

selectedLayers = QgsProject.instance().layerTreeRoot().selectedLayers()

but I get an error about:

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

What's the correct way to get the selected layers in QGIS3?

Best Answer

With the iface object, it is possible to get the layerTreeView, which has a method selectedLayers():

iface.layerTreeView().selectedLayers()

More methods on QgsLayerTreeView in the docs: https://qgis.org/api/classQgsLayerTreeView.html

Related Solutions

PyQGIS – Checking If a Feature is Selected When Iterating Over a Vector Layer

There doesn't seem to be a way to directly find a feature object's parent layer or whether it's selected from a method in the QgsFeature class.

A similar approach to vlayer.selectedFeatures() is to test whether the feat.id() is in vlayer.selectedFeaturesIds(). QgsFeatureIds are not unique values compared with other vector layers, only within their own layer.

Alternatively, you could start with vlayer.selectedFeatures() and iterate over those features, instead of all features of the provider.

Yet another approach is to initially gather sets (or lists) of selected and non-selected feature ids for a given vector layer:

# previous relevant code

set_selids = set(vlayer.selectedFeaturesIds())
feat = QgsFeature()
vlayer.select([], QgsRectangle(), False)
set_allids = set()
while vlayer.nextFeature(feat):
    set_allids.add(feat.id())

set_notselids = set_allids - set_selids

print set_allids
print set_selids
print set_notselids

I can't seem to find a single call for retrieving a reference to all features (or ids) for a vector layer (i.e. still have to use QgsVectorLayer.select() and iterate with QgsVectorLayer.nextFeature()).

I updated the code to reflect QgsVectorLaer can handle select call (no need to get provider directly), and doesn't mess up actual selected features in map canvas, which would require setSelectedFeatures() to update.

After building feature id sets, you can iterate over them and use QgsVectorLayer.featureAtId(featid) to access the feature.

[GIS] Getting attributes of selected features using PyQGIS

This will work:

layer = iface.activeLayer()

features = layer.selectedFeatures()

for f in features:
    print f.attributeMap()

In PyQGIS 3:

layer = iface.activeLayer()

features = layer.selectedFeatures()

for f in features:
    # refer to all attributes
    print (f.attributes()) # results in [3, 'Group 1', 4.6]

for f in features:
    # refer to a specific values of a field index
    print(f.attribute(1)) # results in Group 1

Best Answer

Related Solutions

PyQGIS – Checking If a Feature is Selected When Iterating Over a Vector Layer

[GIS] Getting attributes of selected features using PyQGIS

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