Added check to ensure we are in lighttable view prior to callling darktable.register_lib. If darktable was invoked in single image (darkroom) mode, then an event handler is registered to detect the change from darkroom mode to lighttable mode so that we can then call darktable.register_lib.

contrib/gpx_export.lua

@@ -36,6 +36,10 @@ local function _(msgid)
   return gettext.dgettext("gpx_export", msgid)
 end
 
+local gpx = {}
+gpx.module_installed = false
+gpx.event_registered = false
+
 local path_entry = dt.new_widget("entry")
 {
   text = dt.preferences.read("gpx_exporter", "gpxExportPath", "string"),
@@ -127,31 +131,55 @@ local function create_gpx_file()
   end
 end
 
-dt.register_lib(
-  "gpx_exporter",
-  "gpx export",
-  true, -- expandable
-  true, -- resetable
-  {[dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 100}},   -- containers
+local function install_module()
+  if not gpx.module_installed then
+    dt.register_lib(
+      "gpx_exporter",
+      "gpx export",
+      true, -- expandable
+      true, -- resetable
+      {[dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 100}},   -- containers
+      gpx.widget,
+      nil,-- view_enter
+      nil -- view_leave
+    )
+    gpx.module_installed = true
+  end
+end
+
+gpx.widget = dt.new_widget("box")
+{
+  orientation = "vertical",
+  dt.new_widget("button")
+  {
+    label = _("export"),
+    tooltip = _("export gpx file"),
+    clicked_callback = create_gpx_file
+  },
   dt.new_widget("box")
   {
-    orientation = "vertical",
-    dt.new_widget("button")
+    orientation = "horizontal",
+    dt.new_widget("label")
     {
-      label = _("export"),
-      tooltip = _("export gpx file"),
-      clicked_callback = create_gpx_file
-    },
-    dt.new_widget("box")
-    {
-      orientation = "horizontal",
-      dt.new_widget("label")
-      {
-        label = _("file:"),
-      },
-      path_entry
+      label = _("file:"),
     },
+    path_entry
   },
-  nil,-- view_enter
-  nil -- view_leave
-)
+}
+
+
+if dt.gui.current_view().name == "lighttable" then
+  install_module()
+else
+  if not gpx.event_registered then
+    dt.register_event(
+      "view-changed",
+      function(event, old_view, new_view)
+        if new_view.name == "lighttable" and old_view.name == "darkroom" then
+          install_module()
+         end
+      end
+    )
+    gpx.event_registered = true
+  end
+end