Graphics Reference
In-Depth Information
The qgis.gui package
The
qgis.gui
package defines a number of user-interface widgets that you can include
in your programs. Let's start by looking at the most important
qgis.gui
classes, and fol-
low this up with a brief look at some of the other classes that you might find useful.
The QgisInterface class
QgisInterface
represents the QGIS system's user interface. It allows programmatic ac-
cess to the map canvas, the menu bar, and other parts of the QGIS application. When run-
ning Python code within a script or a plugin, or directly from the QGIS Python console, a
reference to
QgisInterface
is typically available through the
iface
global variable.
Note
The
QgisInterface
object is only available when running the QGIS application itself.
If you are running an external application and import the PyQGIS library into your applica-
tion,
QgisInterface
won't be available.
Some of the more important things you can do with the
QgisInterface
object are:
• Get a reference to the list of layers within the current QGIS project via the
le-
gendInterface()
method.
• Get a reference to the map canvas displayed within the main application window,
using the
mapCanvas()
method.
• Retrieve the currently active layer within the project, using the
activeLayer()
method, and set the currently active layer by using the
setActiveLayer()
method.
• Get a reference to the application's main window by calling the
mainWindow()
method. This can be useful if you want to create additional Qt windows or dialogs
that use the main window as their parent.
• Get a reference to the QGIS system's message bar by calling the
messageBar()
method. This allows you to display messages to the user directly within the QGIS
main window.
The QgsMapCanvas class
The
map canvas
is responsible for drawing the various map layers into a window. The
QgsMapCanvas
class represents a map canvas. This class includes:
