Merge pull request PramodJoshi#44 from itaishalom/master

If the value is canceled, onToggle should return null, not the index.

Author: PramodJoshi

example/lib/main.dart

@@ -26,6 +26,7 @@ class MyApp extends StatelessWidget {
                   ),
                   ToggleSwitch(
                     initialLabelIndex: 0,
+                    doubleTapDisable: true,
                     totalSwitches: 3,
                     labels: ['America', 'Canada', 'Mexico'],
                     onToggle: (index) {
@@ -113,8 +114,9 @@ class MyApp extends StatelessWidget {
                   ToggleSwitch(
                     minWidth: 90.0,
                     minHeight: 70.0,
-                    initialLabelIndex: 2,
+                    initialLabelIndex: null,
                     cornerRadius: 20.0,
+                    doubleTapDisable: true,
                     activeFgColor: Colors.white,
                     inactiveBgColor: Colors.grey,
                     inactiveFgColor: Colors.white,

lib/toggle_switch.dart

@@ -3,7 +3,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
-typedef OnToggle = void Function(int index);
+typedef OnToggle = void Function(int? index);
 
 // ignore: must_be_immutable
 class ToggleSwitch extends StatefulWidget {
@@ -337,15 +337,21 @@ class _ToggleSwitchState extends State<ToggleSwitch>
 
   /// Handles selection
   void _handleOnTap(int index) async {
+    bool notifyNull = false;
     if (widget.changeOnTap) {
       if (widget.doubleTapDisable && widget.initialLabelIndex == index) {
         setState(() => widget.initialLabelIndex = null);
+        notifyNull = true;
       } else {
         setState(() => widget.initialLabelIndex = index);
       }
     }
     if (widget.onToggle != null) {
-      widget.onToggle!(index);
+      if (notifyNull) {
+        widget.onToggle!(null);
+      } else {
+        widget.onToggle!(index);
+      }
     }
   }