问GetX -如何从Get.Dialog返回值？

EN

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return GetMaterialApp( // <-- Use GetMaterialApp
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Examples'),
    );
  }
}

E/flutter (11139): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: 
'package:flutter/src/widgets/localizations.dart': Failed assertion: 
line 453 pos 12: 'context != null': is not true.

onPressed: () async {
  // assign return value to an observable
  return lx.result.value = await Get.dialog(

onPressed: () => Get.back(result: true),

import 'package:flutter/material.dart';
import 'package:get/get.dart';

class LoginX extends GetxController {
  RxBool result = false.obs;
}

class GetDialogReturnPage extends StatelessWidget {
  final LoginX lx = Get.put(LoginX());

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('GetDialog Return Example'),
      ),
      body: SafeArea(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.center,
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Container(
              child: Obx(() => Text('Value shows here: ${lx.result.value}')),
            ),
            Container(
              alignment: Alignment.center,
              child: RaisedButton(
                child: Text('Login'),
                onPressed: () async {
                  // ** assign return value to an observable **
                  return lx.result.value = await Get.dialog(
                      AlertDialog(
                          content: Row(
                            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                            children: [
                              RaisedButton(
                                child: Text('Good Login'),
                                onPressed: () => Get.back(result: true),
                                // ** result: returns this value up the call stack **
                              ),
                              SizedBox(width: 5,),
                              RaisedButton(
                                child: Text('Bad Login'),
                                onPressed: () => Get.back(result: false),
                              ),
                            ],
                          )
                      )
                  );},
              ),
            )
          ],
        ),
      ),
    );
  }
}