Sometimes you need to load an existing project from a plugin or (more often) when developing a standalone QGIS Python application (see: Python Applications).
To load a project into the current QGIS application you need to create
an instance of the
This is a singleton class, so you must use its
instance() method to do it.
You can call its
read() method, passing the path of the project to be loaded:
# If you are not inside a QGIS console you first need to import # qgis and PyQt classes you will use in this script as shown below: from qgis.core import QgsProject # Get the project instance project = QgsProject.instance() # Print the current project file name (might be empty in case no projects have been loaded) print(project.fileName()) '/home/user/projects/my_qgis_project.qgs' # Load another project project.read('/home/user/projects/my_other_qgis_project.qgs') print(project.fileName()) '/home/user/projects/my_other_qgis_project.qgs'
If you need to make modifications to the project (for example to add or remove some layers)
and save your changes, call the
write() method of your project instance.
write() method also accepts an optional
path for saving the project to a new location:
# Save the project to the same project.write() # ... or to a new file project.write('/home/user/projects/my_new_qgis_project.qgs')
If you are writing a QGIS standalone application, in order to synchronise the loaded project with
the canvas you need to instantiate a
QgsLayerTreeMapCanvasBridge as in the example below:
bridge = QgsLayerTreeMapCanvasBridge( \ QgsProject.instance().layerTreeRoot(), canvas) # Now you can safely load your project and see it in the canvas project.read('/home/user/projects/my_other_qgis_project.qgs')