[gnome-music/wip/jfelder/albumwidget-scroll-event] albumWidget: Add scroll-event signal

[Jean Felder <jfelder src gnome org>]

commit 5141f8d8a7dd64270527e1fe5675da5f3a370f39
Author: Jean Felder <jfelder src gnome org>
Date:   Tue Jan 15 03:06:01 2019 +0100

    albumWidget: Add scroll-event signal

 data/ui/AlbumWidget.ui            |  2 +-
 gnomemusic/widgets/albumwidget.py | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)
---
diff --git a/data/ui/AlbumWidget.ui b/data/ui/AlbumWidget.ui
index 04f70b03..7be54065 100644
--- a/data/ui/AlbumWidget.ui
+++ b/data/ui/AlbumWidget.ui
@@ -205,7 +205,7 @@
           </packing>
         </child>
         <child>
-          <object class="GtkScrolledWindow" id="scrolledWindow">
+          <object class="GtkScrolledWindow" id="_scrolled_window">
             <property name="visible">True</property>
             <property name="can_focus">False</property>
             <property name="hexpand">True</property>
diff --git a/gnomemusic/widgets/albumwidget.py b/gnomemusic/widgets/albumwidget.py
index f380ad2e..8134080c 100644
--- a/gnomemusic/widgets/albumwidget.py
+++ b/gnomemusic/widgets/albumwidget.py
@@ -23,7 +23,7 @@
 # delete this exception statement from your version.
 
 from gettext import ngettext
-from gi.repository import GdkPixbuf, GObject, Grl, Gtk
+from gi.repository import Gdk, GdkPixbuf, GObject, Grl, Gtk
 
 from gnomemusic import log
 from gnomemusic.albumartcache import Art
@@ -51,6 +51,7 @@ class AlbumWidget(Gtk.EventBox):
     _cover_stack = Gtk.Template.Child()
     _disc_listbox = Gtk.Template.Child()
     _released_info_label = Gtk.Template.Child()
+    _scrolled_window = Gtk.Template.Child()
     _running_info_label = Gtk.Template.Child()
     _title_label = Gtk.Template.Child()
 
@@ -94,6 +95,9 @@ class AlbumWidget(Gtk.EventBox):
         self.bind_property(
             'selected-items-count', self._parent_view, 'selected-items-count')
 
+        self.add_events(Gdk.EventMask.SCROLL_MASK)
+        self.connect("scroll-event", self._album_widget_scrolled)
+
     @log
     def _create_model(self):
         """Create the ListStore model for this widget."""
@@ -293,3 +297,14 @@ class AlbumWidget(Gtk.EventBox):
         :rtype: Grl.Media
         """
         return self._album
+
+    def _album_widget_scrolled(self, klass, event):
+        direction = event.direction
+        if direction not in [Gdk.ScrollDirection.DOWN, Gdk.ScrollDirection.UP]:
+            return
+
+        delta = -1.0
+        if direction == Gdk.ScrollDirection.DOWN:
+            delta = 1.0
+        vadjust = self._scrolled_window.props.vadjustment
+        vadjust.props.value += delta * vadjust.props.step_increment