A value of type 'Null' can't be assigned to a parameter of type 'Widget Function()' in a const constructor

Question

on the documentation they use it like this :

class WelcomePage extends GetView<WelcomeController> {
  const WelcomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      body: Obx(() => SizedBox(
            width: 360.w,
            height: 780.w,
            child: Stack(
              alignment: Alignment.bottomCenter,
              children: [
                PageView(
                  scrollDirection: Axis.horizontal,
                  reverse: false,
                  onPageChanged: (index) {},
                  controller: PageController(
                      initialPage: 0, keepPage: false, viewportFraction: 1),
                  pageSnapping: true,
                  physics: const ClampingScrollPhysics(),
                  children: const [],
                )
              ],
            ),
          )),
    );
  }
}

but I keep having this error "A value of type 'Null' can't be assigned to a parameter of type 'Widget Function()' in a const constructor. Try using a subtype, or removing the keyword 'const'." error in the constructor of

 Obx( () => )

I want to fix this issue and understand why i got this error.

Answer 1

you have to put some observable value inside the obx for example in your getx controller you have bool isLoading = false.obs; that you need to add anywhere inside the widget that wrapped by Obx or it will throws an error