Add helpful hint text to variable fields widget

client/variablefieldswidget.ui

@@ -101,7 +101,13 @@
         </widget>
        </item>
        <item>
-        <widget class="QListWidget" name="variableFieldList" />
+        <widget class="XListWidget" name="variableFieldList" >
+         <property name="whatsThis" >
+          <string>A variable field is a protocol field which you want to vary across packets
+
+To create one, select the protocol on the left and click '+' above</string>
+         </property>
+        </widget>
        </item>
       </layout>
      </widget>
@@ -264,6 +270,13 @@
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>XListWidget</class>
+   <extends>QListWidget</extends>
+   <header>xlistwidget.h</header>
+  </customwidget>
+ </customwidgets>
  <tabstops>
   <tabstop>protocolList</tabstop>
   <tabstop>variableFieldList</tabstop>

client/xlistwidget.h

@@ -0,0 +1,48 @@
+/*
+Copyright (C) 2018 Srivats P.
+
+This file is part of "Ostinato"
+
+This 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 3 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, see <http://www.gnu.org/licenses/>
+*/
+
+#ifndef _X_LIST_WIDGET_H
+#define _X_LIST_WIDGET_H
+
+#include <QListWidget>
+
+#include <QPainter>
+
+class XListWidget : public QListWidget
+{
+public:
+    XListWidget(QWidget *parent) : QListWidget(parent) {}
+    virtual ~XListWidget() {}
+
+protected:
+    virtual void paintEvent(QPaintEvent *event)
+    {
+        if (!model()->hasChildren())  {
+            QPainter painter(viewport());
+            style()->drawItemText(&painter, viewport()->rect(),
+                    layoutDirection() | Qt::AlignCenter, palette(),
+                    true, whatsThis(), QPalette::WindowText);
+        }
+        else
+            QListWidget::paintEvent(event);
+    }
+};
+
+#endif
+