How to handle null error of WillPopScope widget when press back button?-CodePudding

I use WillPopScope widget into Home Page Screen to prevent app from exiting. When user press back button without confirmation alert dialog

body: WillPopScope(
  onWillPop: () => StaticUI()
      .onScreenPop(Routes.customerProcessScreen, context) as Future<bool>,
  child: SingleChildScrollView(
  ...
),
);

Future<bool>? onScreenPop(String route, BuildContext context) async => await showDialog(
  useSafeArea: true,
  context: context,
  barrierDismissible: true, // user must tap button!
  builder: (BuildContext context) {
    return Stack(
      children: [
           ...
      ],
    );
  },
);

But I get a null error when I press back button to dismiss alert (when closing alert)!


E/flutter ( 4688): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: type 'Null' is not a subtype of type 'FutureOr<bool>'
E/flutter ( 4688): #0      StaticUI.onScreenPop (package:hesabate/Utils/statics.dart:275:74)
E/flutter ( 4688): <asynchronous suspension>
E/flutter ( 4688): #1      ModalRoute.willPop (package:flutter/src/widgets/routes.dart:1357:11)
E/flutter ( 4688): <asynchronous suspension>
E/flutter ( 4688): #2      NavigatorState.maybePop (package:flutter/src/widgets/navigator.dart:4966:45)
E/flutter ( 4688): <asynchronous suspension>
E/flutter ( 4688):

SDK version

environment:
  sdk: '>=2.12.0 <3.0.0'

CodePudding user response：

You need to return either true or false from the onScreenPop function. To do that make sure you return either true or false from your showDialog. Refer this link to learn more about how to return values from showDialog in flutter.

CodePudding user response：

I did some edits in my code to check for null returns , so it's working now .

Future<bool> onScreenPop(String route, BuildContext context) async {
final result = await showDialog(
  useSafeArea: true,
  context: context,
  barrierDismissible: true, // user must tap button!
  builder: (BuildContext context) {
    return Stack(
      children: [
        ...
      ],
    );
  },
);

   if (result == null) {
     return false;
    } else {
     return result;
    }
}