Choosing layers to dump in legend for a standalone application

Question

I'm writing a standalone application using QGIS API to export maps automatically as pdf.

When I'm building my QgsComposition, I have an issue:

I have already built a list with the layers I want to show on the map (not all the layers from the original project), but my QgsComposerLegend shows all the layers.

First, I tried this:

    legend = QgsComposerLegend(c)
    legend.setTitle(u"Légende:")
    legend.model().setLayerSet(renderer.layerSet())
    [...]
    c.addComposerLegend(legend)

And the result:

But the layer set is not the one I want.

I found this post: Filter MapComposer legend to only show layers visible on the map

I adapted its code to mine and I have this:

With the code:

    legend = QgsComposerLegend(c)
    legend.setTitle(u"Légende:")
    layerGroup = QgsLayerTreeGroup()
    for layer in layers:
        layerGroup.insertLayer(0, layer)
    legend.modelV2().setRootGroup(layerGroup)
    [...]
    c.addComposerLegend(legend)

The issue is that I would keep the initial tree organization, and just suppress the layers I don't want.

I tried using the QgsLayerTreeGroup methods this way:

    legend = QgsComposerLegend(c)
    legend.setTitle(u"Légende:")
    layersToRemove = []
    for layer in legend.modelV2().rootGroup().findLayers():
        if layer.layer() not in layers:
            layersToRemove.append(layer.layer())
    for layer in layerToRemove:
        # print(layer.id())
        legend.modelV2().rootGroup().removeLayer(layer)
    [...]
    c.addComposerLegend(legend)

But I have the same result as the first code... I don't understand why, but the layers are not removed from the tree... Any idea ?

Answer 1

OK I managed to solve the problem...

To set my layerTree in the legend, I tried to modify directly the layerTreeRoot of the project (I work with a copy of the original project, the layers are never deleted...)

I have built a recursive function to check if each layer in the tree is in my list, and if not, I remove it.

The main code now looks like this:

    legend = QgsComposerLegend(c)
    legend.setTitle(u"Légende:")
    root = buildLegendLayerTree(project.layerTreeRoot(), layers)
    legend.modelV2().setRootGroup(root)
    [...]
    c.addComposerLegend(legend)

With the following definition for the function:

    def buildLegendLayerTree(root, layers):
        for child in root.children():
            if child.nodeType()==0: # if the child is a group node, not a layer
                child = buildLegendLayerTree(child, layers)
            else: # if it is a layer
                if child.layer() not in layers:
                    root.removeChildNode(child)
        return(root)

And now I have the result I expected :)