Programmatically change layer position in the table of contents (QGIS)

Question

I am trying move/position a layer to the bottom of the TOC by using addTopLevelItem on all other layers. I unsure how to reference the layers as QTreeWidgetItem's.

def bg_bottom_level_item(self):
    layers = self.canvas.layers()
    layerlist = []
    for layer in layers:
        layerID = str(layer.id())
        if "Auto_Background" not in layerID:
            layerlist.append(layer)
        else:
            pass
    for layer in layerlist:
        leg = qgis.utils.iface.mainWindow().findChild(QTreeWidget, 'theMapLegend')
        item = QTreeWidgetItem(layer)
        leg.addTopLevelItem(item)

Error:

QTreeWidgetItem(QTreeWidgetItem): argument 1 has unexpected type 'QgsRasterLayer'

Or does anyone have another solution for moving layers around in the TOC?

Check out this post, http://gis.stackexchange.com/questions/41977/sort-layers-in-qgis-table-of-contents — artwork21, Apr 17 '14 at 12:18

score 6 · Accepted Answer · edited Jan 17 '22 at 11:42

6

By using the new Layer tree (aka legend or Toc) added by Martin Dobias since QGIS v.2.4, you can load a layer to the bottom of the ToC following these steps:

Get a reference of the layer tree

root = QgsProject.instance().layerTreeRoot()

Create the layer object

mylayer = QgsVectorLayer("/Path/to/your/data.shp", "my layer", "ogr")

Add the layer to the QGIS Map Layer Registry

QgsMapLayerRegistry.instance().addMapLayer(mylayer, False)

Append the layer to the layer tree
```
root.addLayer(mylayer)
```

If you want to move an existing layer to the bottom of the ToC, you need to know the layer id (you can get it by executing root.findLayerIds()). Once you get the layer id, follow these steps:

a. Same as 1.

root = QgsProject.instance().layerTreeRoot()

b. Get layer by id

myExistingLayer = root.findLayer("divipola_mpio20141217144143371")

c. Clone it (trust me)

myClone = myExistingLayer.clone()

d. Append the clone to the layer tree

root.addChildNode(myClone)

e. Get the original layer's parent

parent = myExistingLayer.parent()

f. Remove the original layer

parent.removeChildNode(myExistingLayer)

Edit: Now steps a. to f. should work for any layer/group regardless of its position in the layer tree hierarchy.

edited Jan 17 '22 at 11:42

Kadir Şahbaz

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answered Dec 17 '14 at 21:06

Germán Carrillo

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Can you explain why we need to clone it? I used this technique, but in a code review got rejected, since I am cloning. – Ely Fialkoff Apr 24 '19 at 13:15
See https://www.lutraconsulting.co.uk/blog/2014/07/25/qgis-layer-tree-api-part-2/ – Germán Carrillo Apr 24 '19 at 14:51
The article doesn't explain why they use clone. – Ely Fialkoff Apr 24 '19 at 17:26
To move a layer in the Layers panel you need to make a copy of the existing layer, insert it at the desired position and then remove the original layer object. To make the copy you use clone. – Germán Carrillo Apr 24 '19 at 17:38
Yes I know all this, but why must we clone it, it seems that making a copy and then deleting the old one creates more overhead than necessary. Why not just have a move method or something without cloning? – Ely Fialkoff Apr 25 '19 at 13:27
You can ask the author of the layer tree component. That's why I sent you the link ;) – Germán Carrillo Apr 25 '19 at 17:00

Programmatically change layer position in the table of contents (QGIS)

1 Answers1