Why does my PyQGIS code for saving selected features result in altered geometries?

Question

In a plugin I want to save the selected features in a new shapefile. I search and I try (How can I create a new layer from the currrent selection? to create a new layer and write the selected fields and features in that:

    vl = QgsVectorLayer("Polygon", "temporary_points", "memory")
    pr = vl.dataProvider()

    # add geometry and fields
    pr.addAttributes(fields)
    pr.addFeatures(features)

But this result is not what I wanted. I get this:

In this image, the selected polygon is yellow and the pink polygon is the saved one as another shapefile. So the geometry is not completely correct and I need the perfect copy of the original.

Anyone knows how to get it?

---

I can use the algorithm from Processing Toolbox, "Save selected features".

Answer 1

You can save selected features from your active layer into a Shapefile simply calling QgsVectorFileWriter.writeAsVectorFormat and passing the onlySelected parameter as True:

layer = iface.activeLayer()
res = QgsVectorFileWriter.writeAsVectorFormat( layer,
                                               '/tmp/selectedFeatures.shp',
                                               'System',
                                               None, #crs
                                               'ESRI Shapefile',
                                               True #onlySelected
                                             )
if res != QgsVectorFileWriter.NoError:
    print 'Error number:', res
else:
    print "Done!"

The resulting layer will contain all fields from source layer.