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

[Giuseppe Sucameli]

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
>
>
>
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-- 
Giuseppe Sucameli