setState() or markNeedsBuild() called during build during build 以及如何解决它

Question

构建过程中调用的setState()或markNeedsBuild()以及如何解决。你能解释一下这个吗---------------------------------------- ---------------------------------------------- ---------------------------------------------- ---------------------------------------------- ---------------------------------------------- ---------------------------------------------- -

import 'package:dishes_app/Dummy_data.dart';
import 'package:dishes_app/Screens/Categories_screen.dart';
import 'package:dishes_app/Screens/Category_meals_screen.dart';
import 'package:dishes_app/Screens/filter_screen.dart';
import 'package:dishes_app/Screens/meal_detail_screen.dart';
import 'package:dishes_app/Screens/tab_screen.dart';
import 'package:flutter/material.dart';

import 'models/meal.dart';

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

class MyApp extends StatefulWidget {
  // This widget is the root of your application.
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  Map<String, bool> _filters = {
    'gluten': false,
    'lactose': false,
    'vegan': false,
    'vegetarian': false,
  };

  List<Meal> _availablemeals = DUMMY_MEALS;

  void _setFilters(Map<String, bool> filterData) {
    setState(() {
      _filters = filterData;
      _availablemeals = DUMMY_MEALS.where((meal) {
        if (_filters['gluten']! && !meal.isGlutenFree) {
          return false;
        }
        if (_filters['lactose']! && !meal.isLactoseFree) {
          return false;
        }
        if (_filters['vegan']! && !meal.isVegan) {
          return false;
        }
        if (_filters['vegetarian']! && !meal.isVegetarian) {
          return false;
        }
        return true;
      }).toList();
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
          primaryColor: Colors.blue,
          accentColor: Colors.amber,
          canvasColor: Color.fromRGBO(255, 254, 229, 1),
          fontFamily: 'Raleway',
          textTheme: ThemeData.light().textTheme.copyWith(
                body1: TextStyle(
                  color: Color.fromRGBO(20, 51, 51, 1),
                ),
                body2: TextStyle(color: Color.fromRGBO(20, 51, 51, 1)),
                title: TextStyle(
                  fontSize: 20,
                  fontFamily: 'RobotoCondensed',
                  fontWeight: FontWeight.bold,
                ),
              )),
      routes: {
        '/': (ctx) => TabsScreen(),
        CategoryMealsScreen.routeName: (ctx) =>
            CategoryMealsScreen(_availablemeals),
        MealDetailScreen.routeName: (ctx) => MealDetailScreen(),
        FilterScreen.routeName: (ctx) =>
            FilterScreen(_setFilters(_filters) as Function(Map)),
      },
      onGenerateRoute: (settings) {
        print(settings.arguments);
      },
      onUnknownRoute: (settings) {
        return MaterialPageRoute(builder: (ctx) => CategoriesScreen());
      },
    );
  }
}

Answer 1

如果您在构建方法完成之前显示快餐栏或警告对话框，以及在许多其他情况下，您可能会遇到此错误。所以在这种情况下使用下面的回调函数。

WidgetsBinding.instance.addPostFrameCallback((_){
  // To do
 });

Answer 2

这一行：

FilterScreen.routeName: (ctx) =>
            FilterScreen(_setFilters(_filters) as Function(Map)),

_setFilters(_filters) 实际上是在调用函数本身，而不是像它应该的那样将函数作为参数传递。如果这正是您想要在函数中执行的操作，则创建一个匿名调用，如下所示：

FilterScreen.routeName: (ctx) =>
           FilterScreen((){_setFilters(_filters);} as Function(Map)),

根据您的 FilterScreen，您可以直接传递 _setFilters，但这样您将无法预先提供任何参数。

setState() or markNeedsBuild() called during build during build 以及如何解决它

setState() or markNeedsBuild() called during build during build and how to resolve it

dart

flutter

flutter-test