def layer_changed(self, layer):
        """Enable or disable keywords editor icon when active layer changes.

        :param layer: The layer that is now active.
        :type layer: QgsMapLayer
        """
        if not layer:
            enable_keyword_wizard = False
        elif not hasattr(layer, 'providerType'):
            enable_keyword_wizard = False
        elif layer.providerType() == 'wms':
            enable_keyword_wizard = False
        else:
            enable_keyword_wizard = True

        try:
            if layer:
                if is_raster_layer(layer):
                    enable_field_mapping_tool = False
                else:
                    keywords = KeywordIO().read_keywords(layer)
                    keywords_version = keywords.get('keyword_version')
                    if not keywords_version:
                        supported = False
                    else:
                        supported = (
                            is_keyword_version_supported(keywords_version))
                    if not supported:
                        enable_field_mapping_tool = False
                    else:
                        layer_purpose = keywords.get('layer_purpose')

                        if not layer_purpose:
                            enable_field_mapping_tool = False
                        else:
                            if layer_purpose == layer_purpose_exposure['key']:
                                layer_subcategory = keywords.get('exposure')
                            elif layer_purpose == layer_purpose_hazard['key']:
                                layer_subcategory = keywords.get('hazard')
                            else:
                                layer_subcategory = None
                            field_groups = get_field_groups(
                                layer_purpose, layer_subcategory)
                            if len(field_groups) == 0:
                                # No field group, disable field mapping tool.
                                enable_field_mapping_tool = False
                            else:
                                enable_field_mapping_tool = True
            else:
                enable_field_mapping_tool = False
        except (KeywordNotFoundError, NoKeywordsFoundError, MetadataReadError):
            # No keywords, disable field mapping tool.
            enable_field_mapping_tool = False

        self.action_keywords_wizard.setEnabled(enable_keyword_wizard)
        self.action_field_mapping.setEnabled(enable_field_mapping_tool)
Enable or disable keywords editor icon when active layer changes.

        :param layer: The layer that is now active.
        :type layer: QgsMapLayer