Field list in combobox in pyqgis

Question

I'm new to pyqgis and I'm tryig to make a combobox with list of fields (from layer also selected in combobox).

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

The problem is, that in second combobox there are fields from first on layerlist layer, not the selected one.

Answer 1

Basically, you have to use signals to detect the "change layer" event and update your field combobox accordingly. Here is a simplified example (assuming you already have the run and initGui methods defined):

In run(self):

layers = QgsMapLayerRegistry.instance().mapLayers().values() # Create list with all layers
# layers = self.iface.legendInterface().layers() might also work
for layer in layers:
    self.dlg.layerComboBox.addItem( layer.name(), layer )

Then, connect the "layer changed" event to a new onLayerChange method, in initGui(self):

self.dlg.layerComboBox.activated.connect( self.onLayerChange )

Then you have to define the onLayerChange(self) method:

def onLayerChange(self, index):

    self.dlg.attributeComboBox.clear() # clears the combobox
    layer = self.dlg.layerComboBox.itemData( index ) # gets selected layer
    for field in layer.pendingFields():
        self.dlg.attributeComboBox.addItem( field.name(), field ) # lists layer fields