Map canvas overlay layers QGIS

Question

I built my own map canvas inside a plugin in QGIS and I want to add two layers (one by one) in order to overlay the two. I have this code:

fileCI = "....\plugins\teste\test.shp"
fileInfo = QFileInfo(fileCI)
layer = QgsVectorLayer(fileCI, fileInfo.baseName(), "ogr")

if not layer.isValid():
    return

if self.canvas.layerCount()==0:

    # add layer to the registry
    QgsMapLayerRegistry.instance().addMapLayer(layer, False)

    # set extent to the extent of our layer
    self.canvas.setExtent(layer.extent())

    # set the map canvas layer set
    self.canvas.setLayerSet([QgsMapCanvasLayer(layer)])
    self.canvas.setVisible(True)    

else:
    layers = self.canvas.layers()
    layers.insert(1,layer)

    # add layer to the registry
    QgsMapLayerRegistry.instance().addMapLayers(layers,False) 

    for i in range(0,self.canvas.layerCount()+1):
        self.canvas.setLayerSet([QgsMapCanvasLayer(layers[i])])
        self.canvas.setVisible(True)

    for lay in layers:
        lay.triggerRepaint()   

But when I add the first vector file, ok, when I add the second the map canvas stay empty.

How do I do to overlay the two layers?

Answer 1

I find a way of overlay vector files (if there is a vector file already open) and a raster file.

orto = '...image.tif'
fileCV = '.../layer1.shp'
layers =  []

# display file in canvas
fileInfo = QFileInfo(fileCV)
layer = QgsVectorLayer(fileCV, fileInfo.baseName(), "ogr")

# raster layer
rfileInfo = QFileInfo(orto)
rlayer = QgsRasterLayer(orto, rfileInfo.baseName())          

if self.canvas.layerCount()==0:

    QgsMapLayerRegistry.instance().addMapLayer(rlayer)
    self.canvas.setExtent(rlayer.extent())   

    # list of layers append raster
    cl_raster= QgsMapCanvasLayer(rlayer)
    layers.append(cl_raster)        

    # add vector layer
    if not layer.isValid():
        return

    QgsMapLayerRegistry.instance().addMapLayer(layer)     
    v_layer = QgsMapCanvasLayer(layer)
    layers.insert(0, v_layer) 

    # show layers
    self.canvas.setLayerSet(layers)            

else:
    existent_layers = self.canvas.layers()
    for i in existent_layers:
        if i.type() == QgsMapLayer.VectorLayer:
            l = QgsMapCanvasLayer(i)
    layers.insert(0, l)


    QgsMapLayerRegistry.instance().addMapLayer(rlayer)
    self.canvas.setExtent(rlayer.extent())   

    # list of layers append raster
    cl_raster= QgsMapCanvasLayer(rlayer)
    layers.insert(2,cl_raster)             

    # add layer to the registry
    QgsMapLayerRegistry.instance().addMapLayer(layer) 

    v_layer = QgsMapCanvasLayer(layer)
    layers.insert(1, v_layer) 

    # show layers
    self.canvas.setLayerSet(layers) 

Thanks for the help!

Answer 2

I don't know if I understand, but... I don't know the reason you try to control canvas layerSet if your goal seems only to show these layers.

I would try simplifing removin if...else and leaning only:

QgsMapLayerRegistry.instance().addMapLayer(layer)

observe that I removed the False parameter so the same registry emit event that allow canvas to automatically update.

you can also add the following row:

self.canvas.setExtent(layer.extent())

to set the extent to the loaded layer as you did in the if statement