[Qgis-developer] how to add a new field to an existing layer?

[Martin Dobias]

On Wed, Aug 11, 2010 at 1:49 AM, Ricardo Filipe Soares Garcia da
<ricardo.garcia.silva at gmail.com> wrote:
>
> provider = pointLayer.dataProvider()
> newField = QgsField("channel", QVariant.Double)
> provider.addAttributes([newField])
> newFieldIndex = provider.fieldNameIndex(newField.name())
> #more code
> allAttrs = provider.attributeIndexes()
> provider.select(allAttrs)
> feat = QgsFeature()
> while provider.nextFeature(feat):
>    # more code, calculating the value of the 'channelValue' variable
>    values = {feat.id() : {newFieldIndex: QVariant(channel)}}
>    provider.ChangeAttributeValues(values)

Btw. for a better performance, it is good to only fill the new values
into the 'values' dictionary within the 'while' cycle. Afterwards you
can run changeAttributeValues() once to modify all features. Anyway if
you do not work with lots of features, it is not so imporant.

Martin