如何从另一个文件中导入一个类，以调用Dart/Flutter中的未来

Question

我想我在这里遗漏了一些很明显的东西，或者我不理解Dart的逻辑，但是我如何从另一个文件引用一个未来值。

例如：

在下面的类中，我将在一个名为home.dart的文件中获得以下信息；

import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;


class Ken extends StatefulWidget {
  const Ken({Key? key}) : super(key: key);

  @override
  KenState createState() => KenState();
}

class KenState extends State<Ken> {

  Future<dynamic> fetchDd() async {
    var daeUrl = "localhost";
    var daeresponse = await http.get(Uri.parse(daeUrl));
    var daedata = await jsonDecode(daeresponse.body);
    var daew = await daedata['de'];
    // print(daew);
    return daew;
  }

在我的第二个文件页面中。1. file ；

我想我可以打电话给home.dart文件，像这样直接访问未来。

import 'home.dart';


Future<dynamic> timeHere() async {
  KenState kenstate = KenState();
  var h = await kenstate.fetchDd();
  // print(h);
  return h;
}

void main() async {
  var c = await timeHere();
  print(c);
}

相反，我得到以下错误；

../../../../FlutterDev/flutter/packages/flutter/lib/src/material/animated_icons.dart:9:8: Error: Not found: 'dart:ui'
import 'dart:ui' as ui show Paint, Path, Canvas;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/animated_icons.dart:10:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/app.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' as ui;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/app_bar_theme.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/arc.dart:6:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/banner_theme.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/bottom_app_bar_theme.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/bottom_navigation_bar_theme.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/bottom_sheet.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;
       ^
../../../../FlutterDev/flutter/packages/flutter/lib/src/material/bottom_sheet_theme.dart:5:8: Error: Not found: 'dart:ui'
import 'dart:ui' show lerpDouble;

我希望就如何解决这一问题提供任何指导。

先谢了。

Answer 1

状态对象是由框架在膨胀一个StatefulWidget.createState方法以将其插入到树中时调用StatefulWidget方法来创建的。

只有在Dart项目本身，这种使用才是不正确的。

在颤振项目中使用：

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: const PageOne(),
      routes: {
        'page_two': (context) => const PageTwo(),
      },
    );
  }
}

PageOne():

class PageOne extends StatefulWidget {
  const PageOne({Key? key}) : super(key: key);

  @override
  State<PageOne> createState() => PageOneState();
}

class PageOneState extends State<PageOne> {
  String value1 = 'empty';

  Future<String> fetchDd() async {
    await Future.delayed(const Duration(seconds: 1));
    value1 = 'Future String';

    return 'fromPageOne';
  }

  Future getValue() async {
    await fetchDd();
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SizedBox(
        width: double.infinity,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(value1),
            TextButton(
                onPressed: () {
                  getValue();
                },
                child: const Text('Get value')),
            TextButton(
                onPressed: () {
                  Navigator.of(context).pushNamed('page_two');
                },
                child: const Text('Page Two')),
          ],
        ),
      ),
    );
  }
}

PageTwo():

class PageTwo extends StatefulWidget {
  const PageTwo({Key? key}) : super(key: key);

  @override
  State<PageTwo> createState() => _PageTwoState();
}

class _PageTwoState extends State<PageTwo> {
  String value2 = 'empty';

  Future timeHere() async {
    PageOneState pageOneState = PageOneState();

    value2 = await pageOneState.fetchDd();
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SizedBox(
        width: double.infinity,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(value2),
            TextButton(
                onPressed: () {
                  timeHere();
                },
                child: const Text('Get value')),
            TextButton(
                onPressed: () {
                  Navigator.of(context).pop();
                },
                child: const Text('Page Two'))
          ],
        ),
      ),
    );
  }
}