保存状态并防止启动不止一次

Question

我有3页（所有状态窗口小部件）：

• 主页
• 天气页面
• 设置页面

是我从主页到天气页面带有 navigator.pushmed“ ，从天气页面 主页 “ navigator.pop” ，下次我'我试图从主页， initstate 方法 再次称为，再次称为... 我如何仅第一次将其调用，并且每次推入天气页面时都不会被调用？

在这里我的app.dart代码：

import 'package:exomind/src/core/views/home_view.dart';
import 'package:exomind/src/features/weather/presentation/views/weather_view.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import '../injection_container.dart';
import 'core/styles/colors.dart';
import 'features/settings/presentation/bloc/settings_bloc.dart';
import 'features/settings/presentation/views/settings_view.dart';
import 'features/weather/presentation/bloc/weather_bloc.dart';

/// The Widget that configures your application.
class MyApp extends StatelessWidget {
  const MyApp({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // Glue the SettingsController to the MaterialApp.
    //
    // The AnimatedBuilder Widget listens to the SettingsController for changes.
    // Whenever the user updates their settings, the MaterialApp is rebuilt.

    return MultiBlocProvider(
        providers: [
          BlocProvider<WeatherBloc>(
              create: (_) => serviceLocator<WeatherBloc>()),
          BlocProvider<SettingsBloc>(
              create: (_) => serviceLocator<SettingsBloc>()
                ..add(
                  const SettingsLoaded(),
                )),
        ],
        child:
            BlocBuilder<SettingsBloc, SettingsState>(builder: (context, state) {
          return MaterialApp(
            debugShowCheckedModeBanner: false,

            // Providing a restorationScopeId allows the Navigator built by the
            // MaterialApp to restore the navigation stack when a user leaves and
            // returns to the app after it has been killed while running in the
            // background.
            restorationScopeId: 'app',

            // Provide the generated AppLocalizations to the MaterialApp. This
            // allows descendant Widgets to display the correct translations
            // depending on the user's locale.
            localizationsDelegates: const [
              AppLocalizations.delegate,
              GlobalMaterialLocalizations.delegate,
              GlobalWidgetsLocalizations.delegate,
              GlobalCupertinoLocalizations.delegate,
            ],
            supportedLocales: const [
              Locale('en', ''), // English, no country code
            ],

            // Use AppLocalizations to configure the correct application title
            // depending on the user's locale.
            //
            // The appTitle is defined in .arb files found in the localization
            // directory.
            onGenerateTitle: (BuildContext context) =>
                AppLocalizations.of(context)!.appTitle,

            // Define a light and dark color theme. Then, read the user's
            // preferred ThemeMode (light, dark, or system default) from the
            // SettingsController to display the correct theme.
            theme:
                ThemeData(fontFamily: 'Circular', primaryColor: kPrimaryColor),
            darkTheme: ThemeData.dark(),
            themeMode: state.themeMode,

            // Define a function to handle named routes in order to support
            // Flutter web url navigation and deep linking.
            onGenerateRoute: (RouteSettings routeSettings) {
              return MaterialPageRoute<void>(
                settings: routeSettings,
                builder: (BuildContext context) {
                  switch (routeSettings.name) {
                    case SettingsView.routeName:
                      return const SettingsView();
                    case WeatherView.routeName:
                      return const WeatherView();
                    case HomeView.routeName:
                      return const HomeView();
                    default:
                      return const HomeView();
                  }
                },
              );
            },
          );
        }));
  }
}

在这里我的home_view.dart代码：

import 'package:flutter/material.dart';

import '../../features/weather/presentation/views/weather_view.dart';

class HomeView extends StatefulWidget {
  const HomeView({Key? key}) : super(key: key);
  static const routeName = '/home';

  @override
  State<HomeView> createState() => _HomeViewState();
}

class _HomeViewState extends State<HomeView>
    with SingleTickerProviderStateMixin {
  late AnimationController rotationController;

  @override
  void initState() {
    rotationController =
        AnimationController(duration: const Duration(seconds: 1), vsync: this)
          ..repeat();
    super.initState();
  }

  @override
  void dispose() {
    rotationController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final double height = MediaQuery.of(context).size.height;
    final double width = MediaQuery.of(context).size.width;

    return Scaffold(
      body: Stack(
        alignment: Alignment.center,
        children: [
          Positioned(
            top: (height / 2),
            child: RotationTransition(
              turns: Tween(begin: 0.0, end: 1.0).animate(rotationController),
              child: IconButton(
                icon: const Icon(Icons.wb_sunny),
                color: Colors.yellow,
                iconSize: (width * 0.2),
                onPressed: () {
         Navigator.of(context).pushNamed(WeatherView.routeName);
                },
              ),
            ),
          )
        ],
      ),
    );
  }
}

在这里我的weather_view.dart代码：

import 'dart:async';
import 'package:exomind/src/features/weather/presentation/bloc/weather_bloc.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:percent_indicator/percent_indicator.dart';

class WeatherView extends StatefulWidget {
  const WeatherView({Key? key}) : super(key: key);
  static const routeName = '/weather';

  @override
  State<WeatherView> createState() => _WeatherViewState();
}

class _WeatherViewState extends State<WeatherView>
    with SingleTickerProviderStateMixin {

  @override
  void initState() {
    print("initcalled")
    super.initState();
  }

  @override
  void dispose() {
    rotationController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);

    final double width = MediaQuery.of(context).size.width;
    final double height = MediaQuery.of(context).size.height;

    return Scaffold();
  }
}

任何帮助和解释都会受到赞赏： ）

Answer 1

我想不出一种“干净”的方式，即不在_weatherviewState中执行Initstate。您是否试图避免添加到WeatherBloc的同一城市不止一次？如果是这样，在添加之前，我会检查Weatherbloc中的“城市”。

Answer 2

在您的ongenerateroute中，您每次都会调用Weatherview构造函数：

case WeatherView.routeName:
  return const WeatherView();

依次调用Initstate。您需要做的是创建Weatherview page widget一次，然后在ongenerateroute中使用它：

final _weatherView = const WeatherView();

在您的ongererateroute中：

case WeatherView.routeName:
  return _weatherView;

Answer 3

正如@Roslanamir所说，每次我们进入状态范围时，都无法防止被调用。
因此，为了防止每次我们推入已陈述的小部件时，我都会添加到集团中的事件，我会向每个州添加一个布尔变量，以了解是否应该再次添加该事件。
对于那些想要一个精确答案的人，请不要犹豫。

Answer 4

只需在天气页面上添加一个参数：指定Rebuild是 true 或 false 的布尔值。 （如果为true，它将调用initstate（））

此代码正常工作。

class WeatherView extends StatefulWidget {
  final bool rebuild;
  static const routeName = '/weather';

  WeatherView({
    Key? key,
    required this.rebuild,
  }) : super(key: key);

  @override
  State<WeatherView> createState() => _WeatherViewState();
}

WeatherViewState's initstate（）将是：

@override
void initState() {
  if (widget.rebuild) {
    print("initcalled");
    super.initState();
  } else {
    print("Not called");
  }
}

因此，在您的app.dart.dart中，您现在应该通过执行到页面来路由到页面

case WeatherView.routeName:
     return const WeatherView(rebuild: true); //Choose if rebuild or not by true and false