From be5557080b1afb3486568e4d5f169402d87faa92 Mon Sep 17 00:00:00 2001
From: Bill Ferguson <wpferguson@gmail.com>
Date: Sat, 8 Aug 2020 23:38:48 -0400
Subject: [PATCH] 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/transfer_hierarchy.lua | 40 +++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/contrib/transfer_hierarchy.lua b/contrib/transfer_hierarchy.lua
index c2ba9cb..70bb598 100755
--- a/contrib/transfer_hierarchy.lua
+++ b/contrib/transfer_hierarchy.lua
@@ -99,6 +99,10 @@ end
 
 -- Helper functions: BEGIN
 
+local th = {}
+th.module_installed = false
+th.event_registered = false
+
 local function pathExists(path)
    local success, err, errno = os.rename(path, path)
    if not success then
@@ -122,6 +126,16 @@ local function createDirectory(path)
    end
 end
 
+local function install_module()
+  if not th.module_installed then
+    darktable.register_lib(LIB_ID,
+               "transfer hierarchy", true, true, {
+            [darktable.gui.views.lighttable] = { "DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 700 }
+               }, th.transfer_widget, nil, nil)
+    th.module_installed = true
+  end
+end
+
 -- Helper functions: END
 
 
@@ -292,7 +306,7 @@ end
 
 
 
-local transfer_widget = darktable.new_widget("box") {
+th.transfer_widget = darktable.new_widget("box") {
    orientation = "vertical",
    darktable.new_widget("button") {
      label = _("calculate"),
@@ -347,12 +361,18 @@ darktable.preferences.register(
 
 -- Preferences: END
 
-
-
-
-
-
-darktable.register_lib(LIB_ID,
-		       "transfer hierarchy", true, true, {
-			  [darktable.gui.views.lighttable] = { "DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 700 }
-		       }, transfer_widget, nil, nil)
+if darktable.gui.current_view().name == "lighttable" then
+  install_module()
+else
+  if not th.event_registered then
+    darktable.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
+    )
+    th.event_registered = true
+  end
+end