def aggregation(self, layer):
        """Setter for the current aggregation layer.

        :param layer: The current aggregation layer.
        :type layer: QgsVectorLayer
        """
        # We need to disconnect first.
        if self._aggregation and self.use_selected_features_only:
            self._aggregation.selectionChanged.disconnect(
                self.validate_impact_function)

        self._aggregation = layer

        if self.use_selected_features_only and layer:
            self._aggregation.selectionChanged.connect(
                self.validate_impact_function)
Setter for the current aggregation layer.

        :param layer: The current aggregation layer.
        :type layer: QgsVectorLayer