[Qgis-developer] Qgis Api - select all features of a vector layer

[Carson Farmer]

...and with the newer PyQGIS API, we can do things even more Pythonically:

def layerIds(layer):
    layer.select([]) # we don't actually need the attributes
    ids = [feat.id() for feat in layer]
    return ids

Obviously you could skip the step of creating the layerIds function,
and then you'd reduce the entire thing down to:

layer = self.iface.mapCanvas().currentLayer() # or however else you
get the layer
layer.select([]) # we don't actually need the attributes
layer.setSelectedFeatures([feat.id() for feat in layer]) # select all
the feature ids

My guess is that this would be quite a bit faster than boundingbox
method, especially because select(QgsRectangle, bool) actually
contains this:

QgsFeature f;
while ( nextFeature( f ) )
{
  select( f.id(), false );
}

whereas setSelectedFeatures is more direct.

Carson

On 9 November 2010 16:46, Barry Rowlingson <b.rowlingson at lancaster.ac.uk> wrote:
> On Tue, Nov 9, 2010 at 4:22 PM, kimaidou <kimaidou at gmail.com> wrote:
>> Hi again
>>
>> Still working on my python plugin...
>>
>> I need to simply select all the features of a chosen vector layer. In
>> QgsVectorLayer api, there is no method "selectAllFeatures()"
>>
>> So I use this piece of code to achieve it
>> http://osgeo.pastebin.com/Ma9DxgKR
>
>  That's an interesting approach! My selectplus plugin has a 'select
> all' function which does this:
>
>    def doit(self):
>        layer = self.iface.mapCanvas().currentLayer()
>        layer.setSelectedFeatures(layerIds(layer))
>        return None
>
> where layerIds is:
>
> def layerIds(layer):
>    ids = []
>    p = layer.dataProvider()
>    allAttrs = p.attributeIndexes()
>    p.select(allAttrs)
>    f = QgsFeature()
>    while p.nextFeature(f):
>        ids.append(f.id())
>    return ids
>
> Your rectangle overlay should be pretty quick, but maybe my collecting
> all the feature IDs is quicker?
>
> Barry
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-- 
Carson J. Q. Farmer
ISSP Doctoral Fellow
National Centre for Geocomputation
National University of Ireland, Maynooth,
http://www.carsonfarmer.com/