Order of layers in PyQGIS layout function

Question

I'm creating a standalone PyQGIS application with a function to print a layout with all layers on the existing canvas.

Here is the current code for printing all the layers on canvas onto a layout, and then exporting them into a pdf:

def createLayout(Main):
    layers = Main.canvas.layers()
    project = QgsProject.instance()
    manager = project.layoutManager()
    layoutName = 'Layout1'
    layouts_list = manager.printLayouts()
    for layout in layouts_list:
        if layout.name() == layoutName:
            manager.removeLayout(layout)
    layout = QgsPrintLayout(project)
    layout.initializeDefaults()
    layout.setName(layoutName)
    manager.addLayout(layout)

    map = QgsLayoutItemMap(layout)
    map.setRect(20, 20, 20, 20)

    ms = QgsMapSettings()
    ms.setLayers(layers)
    print(ms.layerIds())
    print(layers)
    rect = QgsRectangle(ms.fullExtent())
    rect.scale(1.0)
    ms.setExtent(Main.canvas.extent())
    map.setExtent(Main.canvas.extent())
    layout.addLayoutItem(map)

    map.attemptMove(QgsLayoutPoint(5, 20, QgsUnitTypes.LayoutMillimeters))
    map.attemptResize(QgsLayoutSize(180, 180, QgsUnitTypes.LayoutMillimeters))

    # This exports a Print Layout as an image
    layout = manager.layoutByName(layoutName)

    # This creates a QgsLayoutExporter object
    exporter = QgsLayoutExporter(layout)

    # This exports a pdf of the layout object
    exporter.exportToPdf('C:\\Users\\seteg\\Desktop\\test\\testPDF.pdf', QgsLayoutExporter.PdfExportSettings())

I was following this tutorial https://www.youtube.com/watch?v=h8tNuzHqK2I and it works for the most part. Problem is, in my canvas, there should be two layers, an shp layer and a tiff layer. The shp file should be on top of the tiff file.

This is the output of print(layers):

[<QgsMapLayer: '0-Boundary' (ogr)>, <QgsMapLayer: '1-1-Slope' (gdal)>]

As mentioned in the API for setLayers:(https://qgis.org/pyqgis/3.0/core/Map/QgsMapSettings.html#qgis.core.QgsMapSettings.setLayers)

"Set list of layers for map rendering. The layers must be registered in QgsProject. The layers are stored in the reverse order of how they are rendered (layer with index 0 will be on top)"

My Boundary Layer is index 0 while Slope layer is index 1 but this is my output:

The tiff layer is on top of the boundary layer.

What is the problem here? I have tried reversing the order of layers by replacing layers with layers[::-1] but to no avail.

---

EDIT: running print(ms.layerIds()) give me

'0_Boundary_8deaf683_25ea_4413_ba85_9e932b10db32', '1_1_Slope_3b8789a9_8e2c_4d0f_a81f_ce80955bd4ff']

So I do not know why slope layer is on top of boundary.

Answer 1

For standalone application, for some reason I have to add this line of code:

map.setLayers(layers)

And the layers will appear normally.