Return list of selected items of QListWidget PyQt QGIS

Question

I'm a little bit confused (I'm a newbie) on how to get a list of just the selected Items of a QListWidget (in a QGIS plugin).

I set up the manageGui function in this way:

def manageGui(self):

    selectedLayers = []

    # Trying to set up the listWidgetView
        self.listWidget.setEditTriggers(QtGui.QAbstractItemView.DoubleClicked|QtGui.QAbstractItemView.EditKeyPressed)
        self.listWidget.setSelectionMode(QtGui.QAbstractItemView.MultiSelection)
        self.listWidget.setViewMode(QtGui.QListView.ListMode)

        # Load the layers in the listWidget
        layers = []
        for i in QgsMapLayerRegistry.instance().mapLayers().values():
            #load only POLYGON layers, to filer out useless layers
            if i.geometryType() == QGis.Polygon:
                self.layers.append(i.name())

        # Populate the listWidget with all the polygon layer present in the TOC
        self.listWidget.addItems(self.layers)

        #put the selected layers in a list
        selectedLayers = self.listWidget.selectedItems()

but the listWidget.selectedItems() seems empty. If I print selectedLayers I just get [].

I also tried to run a loop over the listWidget:

        #popultate the list with only the selected layers of the list
        for item in self.listWidget.selectedItems():
            self.selectedLayers.append(item)

but it doesn't work neither, always and empty list.

Answer 1

It seems to me, that you want to fill the list before you even seleceted any items. First you fill it and in the next step you already want the selected items.

You would have to register an event and specify a function what to do at this specific moment. For example when a button is pressed or an item is selected, then you get the selected layers.

Something like:

def get_selected_layers(self):
  selectedLayers = self.listWidget.selectedItems()
  # do the rest of your code

You will find the Qt Signals for the QListWidget in the docs and the easiest way to register the event is in the Qt Designer's Signals and Slots View (F4), where you can connect the Signal to the designated function.

Answer 2

It's easier to do that with an object of the QgsMapLayerComboBox class because the list of layers is automatically incorporated from the detected environment. You can set filters from QgsMapLayerProxyModel class to load only polygon layers. It is so easy that you can use the Python Console to try out the approach.

In my example, I loaded three vector layers (two polygons and one point layer type) in QGIS; as it can be observed at the next image:

I used the next code:

from qgis.gui import *
wcb = QgsMapLayerComboBox()
wcb.setFilters(QgsMapLayerProxyModel.PolygonLayer)
wcb.show()

to get this result:

You can observe that the filter works as it expected. There are only polygon layers at the Combo Box.

In the plugin, the Combo Box is instancied at the __init__ method. The slot function or run method is used to get the layer reference with the 'currentLayer' method of QgsMapLayerComboBox. The following snipped code it is a summary of the procedure:

.
.
.
    def __init__(self, iface):
.
.
.         
        self.wcbL = QgsMapLayerComboBox(self.dlg)
        self.wcbL.move(150,28)
        self.wcbL.setMinimumWidth(203)
        self.wcbL.setFilters(QgsMapLayerProxyModel.PolygonLayer)
.
.
.
    def run(self):
        """Run method that performs all the real work"""
        vlayer = self.wcbL.currentLayer()
.
.
.
        # show the dialog
        self.dlg.show()
.
.
.