QGIS Plugin – How to Automatically Update Field Names Combo Box Using Data from Another Combo Box

pyqgisqgisqgis-plugins

I am creating my very first QGIS plugin using two combo boxes – one to select a layer and the other to select a field.

Whilst the layer selection feature seems to work, the field name combo box is not updated when a new layer is selected.

My code is as follows…

    self.dlg.comboBox.clear()
    self.dlg.comboBox_2.clear()

    layers = self.iface.legendInterface().layers()
    layer_list = []
    for layer in layers:
        layer_list.append(layer.name())
    self.dlg.comboBox.addItems(layer_list)
    selectedLayerIndex = self.dlg.comboBox.currentIndex()
    selectedLayer = layers[selectedLayerIndex]

    fields = [field.name() for field in selectedLayer.pendingFields() ]
    self.dlg.comboBox_2.addItems(fields)

Does anyone happen to know how I can accomplish this?

Best Answer

You could put most of your code in a function which will be run every time a user changes the current layer from the combobox. For example, you could use something like:

self.dlg.comboBox.clear()
self.dlg.comboBox_2.clear()

layers = self.iface.legendInterface().layers()
layer_list = []
for layer in layers:
    layer_list.append(layer.name())
self.dlg.comboBox.addItems(layer_list)

def field_select():
    self.dlg.comboBox_2.clear()
    selectedLayerIndex = self.dlg.comboBox.currentIndex()
    selectedLayer = layers[selectedLayerIndex]
    fields = [field.name() for field in selectedLayer.pendingFields()]
    self.dlg.comboBox_2.addItems(fields)

# This connects the function to the layer combobox when changed
self.dlg.comboBox.currentIndexChanged.connect(field_select)

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I would use a Line Edit widget.

Inside your run() function put something like:

self.selectedLayer = self.iface.activeLayer() # Adjust this to your situation
self.selectedLayer.selectionChanged.connect( self.printSelectedArea )

Then define your printSelectedArea function:

def printSelectedArea( self ):
  area=0
  for f in self.selectedLayer.selectedFeatures(): 
    area += f.geometry().area()
  self.dockwidget.txtArea.setText( str( area ) )

Note that this will print the selected area of your currently selected layer. You would need to adjust the code if you want to add areas across layers, which I didn't see from your question.

When a user chooses a layer in your comboBox you should disconnect the printSelectedArea slot from the previous selected layer and connect it to the new one. You could also disconnect the printSelectedArea slot from any SIGNAL when your plugin is closed or unload. Otherwise, you would end up messing printSelectedArea calls up.

Additionally, you would need to add conditionals to make sure there is a selectedLayer before calling selectedFeatures().

[GIS] ComboBox Field not updating when layer is selected

This is the code snippet in my Test Plugin:

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from qgis.gui import QgsMapLayerComboBox, QgsMapLayerProxyModel, QgsFieldComboBox
.
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    def add_action(
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        self.wcbL = QgsMapLayerComboBox(self.dlg)
        self.wcbL.move(250, 80)
        self.wcbL.setFixedWidth(203)
        self.wcbL.setFilters(QgsMapLayerProxyModel.PointLayer)

        self.wcbF = QgsFieldComboBox(self.dlg)
        self.wcbF.move(250, 120)
        self.wcbF.setFixedWidth(203)

        return action
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    def select_layer_fields(self, vlayer):
        self.wcbF.setLayer(vlayer)
        field = self.wcbF.setLayer(vlayer)

    def run(self):
        """Run method that performs all the real work"""
        vlayer = self.wcbL.currentLayer()
        self.wcbF.setLayer(vlayer)
        self.wcbL.layerChanged.connect(self.select_layer_fields)

        # show the dialog
        self.dlg.show()
        # Run the dialog event loop
        result = self.dlg.exec_()
        # See if OK was pressed
        if result:
            # Do something useful here - delete the line containing pass and
            # substitute with your code.
            pass

I tried it out with two point layers; as it can be observed at following images.

With layer points_test (only one field):

When random_points layer was selected in QgsMapLayerComboBox, fields in this layer were automatically also selected in QgsFieldComboBox object (following image):

Plugin works as expected.

Editing Note 1:

Following image also contains a QgsMapLayerComboBox object added directly with QtDesigner. Its name is mMapLayerComboBox.

Editing Note 2:

When Combo Boxes are adding by using QtDesigner following code works as expected:

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    def change_layers2(self):                                           #new function
        self.dlg.mMapLayerComboBox.clear()
        layers = self.iface.legendInterface().layers()
        layer_list = [ layer.name() for layer in layers ]
        self.dlg.mMapLayerComboBox.addItems(layer_list)

    def select_layer_fields2(self, vlayer):                              #new function
        self.dlg.mFieldComboBox.setLayer(vlayer)
        field = self.dlg.mFieldComboBox.setLayer(vlayer)

    def run(self):
        """Run method that performs all the real work"""
        vlayer = self.wcbL.currentLayer()
        self.wcbF.setLayer(vlayer)
        self.wcbL.layerChanged.connect(self.select_layer_fields)

        vlayer = self.dlg.mMapLayerComboBox.currentLayer()                           #new line
        self.dlg.mFieldComboBox.setLayer(vlayer)                                     #new line
        self.dlg.mMapLayerComboBox.layerChanged.connect(self.select_layer_fields2)   #new line
.
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.

It can be observed at following image:

Best Answer

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