qgis - pyqgis - Editing a feature - Is it possible to set a listener?

is it possible to set a listener that is fired when a feature is edited? What I imagine is this: A geometry is edited (e.g. cut operation) then a listener is fired. This event gives me back the altered geometry. Purpose: A geometry is edited and the current area of the geometry is displayed in a window.

The class QgsVectorLayer provides several listeners (e.g. layerModified). Unfortunately I just get the message that something has been edited, but not the edited feature.

Is there any way to set a listener for a specific feature?

All ideas and suggestions are welcome. (:

Answer

To get information on the changed features use signal committedGeometriesChanges. This gives you the feature id and new geometry of any changed feature of the layer you connect a handler to.

As an example:

def feedback(layerId, changedGeometries):
    for k, v in changedGeometries.items():
        # v contains geometry and it's further usage is up to you
        print 'id: %d, geometry: %s' % (k, v.exportToWkt())

layer = iface.activeLayer()
layer.committedGeometriesChanges.connect(feedback)

Output on console after some editing is saved:

id: 1, geometry: LineString (47.19158866759342175 24.98144494566650309, ...,

     48.26832652730565343 25.72949440609816207)