Patch Setting.ui_theme class method

init.rb

@@ -19,6 +19,7 @@
 require 'theme_changer_my_account_hooks'
 require 'theme_changer_user_patch'
 require 'theme_changer_themes_patch'
+require 'theme_changer_setting_patch'
 
 Rails.configuration.to_prepare do
   # Guards against including the module multiple time (like in tests)

lib/theme_changer_setting_patch.rb

@@ -0,0 +1,19 @@
+module ThemeChangerSetting #:nodoc: all
+  def self.prepended(base)
+    base.singleton_class.prepend ClassMethods
+  end
+
+  module ClassMethods
+    def ui_theme
+      setting = ThemeChangerUserSetting.find_theme_by_user_id(User.current.id)
+      return self[:ui_theme] unless setting
+      if setting.theme == ThemeChangerUserSetting::SYSTEM_SETTING
+        return self[:ui_theme]
+      end
+
+      setting.theme_name
+    end
+  end
+end
+
+Setting.prepend(ThemeChangerSetting) unless Setting.include? ThemeChangerSetting

test/unit/theme_changer_setting_test.rb

@@ -0,0 +1,29 @@
+# Theme Changer plugin for Redmine
+# Copyright (C) 2010-2017  Haruyuki Iida
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+require File.expand_path(File.dirname(__FILE__) + '/../test_helper')
+
+class ThemeChangerSettingTest < ActiveSupport::TestCase
+  fixtures :theme_changer_user_settings, :users
+
+  def setup
+    User.current = User.second
+  end
+
+  def test_setting_ui_theme_returns_custom_user_theme_if_set
+    assert_equal('alternate', Setting.ui_theme)
+  end
+end