按下后退按钮时如何处理 WillPopScope 小部件的空错误？

Question

我将 WillPopScope 小部件用于主页屏幕以防止应用程序退出。当用户在没有确认提示对话框的情况下按下后退按钮时

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: [
           ...
      ],
    );
  },
);

但是当我按下后退按钮关闭警报时（关闭警报时），我得到了一个空错误！


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 版本

environment:
  sdk: '>=2.12.0 <3.0.0'

Answer 1

您需要 return true 或 false 来自 onScreenPop 函数。为此，请确保您 return 来自 showDialog 的 true 或 false。请参阅 this link 以了解有关如何 return 来自 showDialog 的值的更多信息。

Answer 2

我在我的代码中做了一些编辑以检查 null returns，所以它现在可以工作了。

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;
    }
}

按下后退按钮时如何处理 WillPopScope 小部件的空错误？

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

dart

flutter

dart-null-safety