diff --git a/src/chapter2/state_manage.md b/src/chapter2/state_manage.md
index 33775a6c..554309c2 100644
--- a/src/chapter2/state_manage.md
+++ b/src/chapter2/state_manage.md
@@ -128,7 +128,7 @@ class _ParentWidgetState extends State<ParentWidget> {
 //------------------------- TapboxB ----------------------------------
 
 class TapboxB extends StatelessWidget {
-  TapboxB({Key? key, this.active: false, required this.onChanged})
+  TapboxB({Key? key, this.active = false, required this.onChanged})
       : super(key: key);
 
   final bool active;