[Qgis-developer] Basic question: How to select a layer in the GUI and get the handle in the Python code?

[Ole Nielsen]

Hi Giuseppe and Alexander

Thank you for the help - both of you. I followed your instructions and can
now pick file names of loaded layers.

Also, as you suggested, I realised that I needed to study the Qt4 interface
and have gone through most of the tutorials (
http://zetcode.com/tutorials/pyqt4)

The only things I had to change was

   - that the layerCombo lives in 'dlg.ui' and not 'self' since I am using
   a skeleton generated by the plugin generator. Is that OK?
   - that the method in layerCombo to add layers is 'addItem' and not
   'append' :-)

With that loaded layer names show up in the combo and after selection the
fully qualified filename is returned by layer.source()

However, if I want a handle to an active layer, like I got
with self.iface.mapCanvas().currentLayer() is there any way that could be
obtained from the layer object?


Grateful for your advice.

Cheers and thanks

Ole








On Thu, Dec 8, 2011 at 7:46 PM, Giuseppe Sucameli <sucameli at faunalia.it>wrote:

> Hi Ole,
>
> On Thu, Dec 8, 2011 at 3:54 AM, Ole Nielsen
> <ole.moller.nielsen at gmail.com> wrote:
> > I am maybe looking for a file or layer selection combo and
> > a hint on how to make it work.
>
> First create a combo in your UI named "layerCombo"
>
> Then populate the combo running:
>
> self.layers = self.iface.legendInterface().layers()  # store the layer list
> self.layerCombo.clear()  # clear the combo
> for layer in self.layers:    # foreach layer in legend
>    self.layerCombo.append( layer.name() )    # add it to the combo
>
>
> When you have to get the layer selected in the combo,
> just us the following snippet:
>
> index = self.layerCombo.currentIndex()
> if index < 0:
>    # it may occur if there's no layer in the combo/legend
> else:
>    layer = self.layers[ index ]    # get the layer by index from the
> previous stored list
>    source = layer.source()    # get the layer source
>
>
> I haven't tried the previous code, so it could contains errors.
>
> > I have very limited experience with UIs so please forgive me my basic
> > questions.
>
> Look at QT tutorials, they contain everything you need
> to know about UI creation.
>
> Cheers.
>
> >
> > Cheers and thanks
> > Ole
> >
> > On Wed, Dec 7, 2011 at 8:57 PM, Alexander Bruy <alexander.bruy at gmail.com
> >
> > wrote:
> >>
> >> Hi Ole,
> >>
> >> 2011/12/7 Ole Nielsen <ole.moller.nielsen at gmail.com>:
> >> > Sorry, I was perhaps not as clear as I could have been. I have already
> >> > written plugins using the currentLayer option. What I need now is to
> >> > combine
> >> > two layers for a specific analysis. So I imagine being able to select
> >> > them
> >> > through the plugin GUI selection combos and return the two layer
> handles
> >> > to
> >> > the Python code in the same format as what is provided by current
> layer.
> >> > However, I have no idea how to start doing this.
> >>
> >> Ah, understand. That's not so difficult. You need to get layer name
> >> from combobox,
> >> then find layer by name. Here is small function that did this work for
> you
> >>
> >> def getVectorLayerByName( layerName ):
> >>  layerMap = QgsMapLayerRegistry.instance().mapLayers()
> >>  for name, layer in layerMap.iteritems():
> >>    if layer.type() == QgsMapLayer.VectorLayer and layer.name() ==
> >> layerName:
> >>      if layer.isValid():
> >>        return layer
> >>      else:
> >>        return None
> >>
> >> So in your code you can simply do something like this
> >>
> >> layerA = getVectorLayerByName( self.cmbLayerA.currentText() )
> >> layerB = getVectorLayerByName( self.cmbLayerB.currentText() )
> >>
> >> Hope this helps
> >>
> >> --
> >> Alexander Bruy
> >> NextGIS
> >
> >
> >
> > _______________________________________________
> > Qgis-developer mailing list
> > Qgis-developer at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/qgis-developer
> >
>
>
>
> --
> Giuseppe Sucameli
>
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