1

I tried to use QgsProject.instance().addMapLayer(layer) on QGIS 3.4 but I didn't succeed.

Example:

layer = QgsVectorLayer(r'C:\CURSO_PYQGIS\CAPAS\urbano.shp','urbano','ogr ') 
QgsProject.instance().addMapLayer(layer)

But the layer didn't show up, and it didn't give me an error on Python console. I don't understand it, someone knows why?

  • Did you check layer validity before adding it ? By doing layer.isValid() – SIGIS Mar 15 '19 at 8:19
  • There should not be a space after ogr. Change 'ogr ' to 'ogr'. – Joseph Mar 15 '19 at 10:25
  • Thanks Joseph!!! that was the reason "There should not be a space after ogr. Change 'ogr ' to 'ogr'" – Oskar Mar 15 '19 at 12:30
1

The format ("\" instead of "/") of the path could be the cause of your error (see the test below). (I work on Windows and I install Qgis3 with OSGEo4)

This is output of some test I made :

# Here with your format '\'
lyr_error = QgsVectorLayer(r'C:\temp\Parcelles_agricoles_5.shp', 'Parcelles agricole', 'ogr')
# Here with this format "/"
lyr_no_error = QgsVectorLayer(r'C:/temp/Parcelles agricoles_5.shp', 'Parcelles agricole', 'ogr')
# An other format that also valid
lyr_no_error2 = QgsVectorLayer('C:\\temp\\Parcelles agricoles_5.shp', 'Parcelles agricole', 'ogr')
# Test validity
lyr_error.isValid()
>>> False
lyr_no_error.isValid()
>>> True
lyr_no_error2.isValid()
>>> True
# Here it doesn't output anything even no error
QgsProject.instance().addMapLayer(lyr_error)
# Here it output the instance and the layer show up.
QgsProject.instance().addMapLayer(lyr_no_error)
>>> <qgis._core.QgsVectorLayer object at 0x0000000009ED4D38>

I didn't try other type of format but this could be the solution. Hope it helps.

  • Thanks a lot!,your information will help me a lot – Oskar Mar 15 '19 at 12:34
-1

There are some good tutorial about QGIS Python Programming at Geodose. Some tutorials are: Working with Vector Layer ,Add/Delete Field and Updating Attribute Value ,Adding CSV Data,Drawing Marker,Drawing,Polyline and Polygon,Animate GPS Track, Set and Reload Basemap Datasource. Quite good resource.

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