Fix viewer plugin relocation issue (ros-visualization#306)

rqt_bag/src/rqt_bag/timeline_menu.py

@@ -62,6 +62,25 @@ def hideEvent(self, event):
                 item = self.layout().itemAt(0)
                 self.layout().removeItem(item)
 
+    def showEvent(self, event):
+        if self.isVisible():
+            # remove old listener
+            if self._viewer:
+                self._timeline.remove_listener(self._topic, self._viewer)
+                self._viewer = None
+
+            # clean out the layout
+            while self.layout().count() > 0:
+                item = self.layout().itemAt(0)
+                self.layout().removeItem(item)
+
+            # create a new viewer
+            self._viewer = self._viewer_type(self._timeline, self, self._topic)
+            self._timeline.add_listener(self._topic, self._viewer)
+
+            super(TopicPopupWidget, self).show()
+
+
     def show(self, context):
         """
         Make this topic popup visible, if necessary. This includes setting up