0

I would like to construct a GUI using PyQt4 and qgis outside of the main QGIS application. I found this tutorial which provides some indications on how to do this. I am looking to build something similar.

I was able to open up the MapCanvas object as shown in the PyQGIS cookbook using the following script. I also kept the parts where they were adding buttons for zooming, panning, etc

from qgis.gui import *
from qgis.core import *
from qgis.PyQt.QtGui import QAction
from qgis.PyQt.QtCore import SIGNAL, Qt
from qgis.PyQt.QtWidgets import QMainWindow

class MyWnd(QMainWindow):
    def __init__(self, layer):
        QMainWindow.__init__(self)

        self.canvas = QgsMapCanvas()
        self.canvas.setCanvasColor(Qt.white)

        self.canvas.setExtent(layer.extent())
        #self.canvas.setLayers([layer])

        self.setCentralWidget(self.canvas)

        self.actionZoomIn = QAction("Zoom in", self)
        self.actionZoomOut = QAction("Zoom out", self)
        self.actionPan = QAction("Pan", self)

        self.actionZoomIn.setCheckable(True)
        self.actionZoomOut.setCheckable(True)
        self.actionPan.setCheckable(True)

        self.actionZoomIn.triggered.connect(self.zoomIn)
        self.actionZoomOut.triggered.connect(self.zoomOut)
        self.actionPan.triggered.connect(self.pan)

        self.toolbar = self.addToolBar("Canvas actions")
        self.toolbar.addAction(self.actionZoomIn)
        self.toolbar.addAction(self.actionZoomOut)
        self.toolbar.addAction(self.actionPan)

        # create the map toolsq
        self.toolPan = QgsMapToolPan(self.canvas)
        self.toolPan.setAction(self.actionPan)
        self.toolZoomIn = QgsMapToolZoom(self.canvas, False) # false = in
        self.toolZoomIn.setAction(self.actionZoomIn)
        self.toolZoomOut = QgsMapToolZoom(self.canvas, True) # true = out
        self.toolZoomOut.setAction(self.actionZoomOut)

        self.pan()

    def zoomIn(self):
        self.canvas.setMapTool(self.toolZoomIn)

    def zoomOut(self):
        self.canvas.setMapTool(self.toolZoomOut)

    def pan(self):
        self.canvas.setMapTool(self.toolPan)

QgsApplication.setPrefixPath(r"C:\Program Files\QGIS 2.18", True)
qgs = QgsApplication([], True)
qgs.initQgis()
layer = QgsVectorLayer(r'path\to\layer\layername', 'layername')

w = MyWnd(layer)
w.show()

qgs.exec_()
qgs.exitQgis()

When I run this I get the MapCanvas in a GUI type environment with no issues. However if I uncomment line 15 self.canvas.setLayers([layer]) I get an error message:

>>> execfile('test.py')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "test.py", line 60, in <module>
    w = MyWnd(layer)
  File "test.py", line 15, in __init__
    self.canvas.setLayers([layer])
AttributeError: 'QgsMapCanvas' object has no attribute 'setLayers'

Why does this occur?

How can I set layers to the MapCanvas outside of the qgis application?


Following an answer below I have modified line 15 to self.canvas.setLayerSet([QgsMapCanvasLayer(layer)]) however what I am getting now is a blank map canvas with nothing on it.

Why is this occuring?

4

The reason is, you are trying to use QGIS 3 API on QGIS 2.

Here is the API for QGIS 2:

https://qgis.org/api/2.18/classQgsMapCanvas.html

Here is the API for QGIS 3:

https://qgis.org/api/classQgsMapCanvas.html

There are 2 solutions to this problem:

  • Use mapCanvas.setLayerSet
  • Work with QGIS 3
  • You're right, I was blindly copying the code from the cookbook without actually adapting it to my current QGIS version. I have edited the question to reflect this, however now I am getting a blank map... – user32882 Sep 10 '18 at 9:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.