Update three_column_navigation.dart

Author: rodydavis

lib/templates/3-column/three_column_navigation.dart

@@ -6,10 +6,13 @@ class ThreeColumnNavigation extends StatefulWidget {
  ThreeColumnNavigation({
  @required this.sections,
  this.showDetailsArrows = true,
+ this.expandedIconData = Icons.fullscreen_exit,
+ this.collapsedIconData = Icons.fullscreen,
  }) : _adaptive = false;
  List<MainSection> sections;
  final bool _adaptive;
  final bool showDetailsArrows;
+ final IconData expandedIconData, collapsedIconData;
  @override
  _ThreeColumnNavigationState createState() => _ThreeColumnNavigationState();
 }
@@ -63,7 +66,7 @@ class _ThreeColumnNavigationState extends State<ThreeColumnNavigation> {
  child: Scaffold(
  appBar: AppBar(
  leading: IconButton(
- icon: Icon(Icons.menu),
+ icon: Icon(widget.expandedIconData),
  onPressed: () {
  if (mounted)
  setState(() {
@@ -104,7 +107,7 @@ class _ThreeColumnNavigationState extends State<ThreeColumnNavigation> {
  appBar: AppBar(
  leading: !_expanded && constraints.maxWidth >= 720
  ? IconButton(
- icon: Icon(Icons.menu),
+ icon: Icon(widget.collapsedIconData),
  onPressed: () {
  if (mounted)
  setState(() {