小编Jav*_*haq的帖子

我在运行 Flutter 应用程序时收到以下警告。请指导如何修复它

Warning: Your Flutter application is created using an older version of the Android
embedding. It's being deprecated in favor of Android embedding v2.

在 Flutter 中如何仅设置底部边框，

如下图所示，我有一个带有文本的容器，从底部显示红色边框，请指导如何仅从底部设置边框。

如何使用最新的按钮小部件 ElevatedButton 创建具有文本和图标的按钮。

使用 Dart 如何删除字符串开头和结尾的空格？

 String name =" Well Wisher ";

或这个

 String name =" Well Wisher";

或由此

String name ="Well Wisher ";

运行时pod install出现以下错误

[!] CocoaPods could not find compatible versions for pod "OneSignalXCFramework":
  In Podfile:
    onesignal_flutter (from `.symlinks/plugins/onesignal_flutter/ios`) was resolved to 3.2.7, which depends on
      OneSignalXCFramework (= 3.9.1)

None of your spec sources contain a spec satisfying the dependency: `OneSignalXCFramework (= 3.9.1)`.

You have either:
 * out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.
 * mistyped the name or version.
 * not added the source repo that hosts the Podspec to …

在 android Studio 中选择时Create New Flutter Project，会出现 4 个选项，如下所示。

• Flutter Application
• Flutter Plugin
• Flutter Package
• Flutter Module

所有这些 Flutter 项目类型之间有什么区别

Dart Flutter 中的零参数构造函数是什么？

在颤振中创建一个块时，我收到以下错误

  The superclass 'Bloc<QuoteEvent, QuoteState>' doesn't have a zero argument constructor.
Try declaring a zero argument constructor in 'Bloc<QuoteEvent, QuoteState>', or explicitly invoking a different constructor in 'Bloc<QuoteEvent, QuoteState>'.

请指导如何修复它。谢谢

下面是代码

import 'package:meta/meta.dart';
import 'package:bloc/bloc.dart';

import 'package:random_quote/repositories/repositories.dart';
import 'package:random_quote/models/models.dart';
import 'package:random_quote/bloc/bloc.dart';

class QuoteBloc extends Bloc<QuoteEvent, QuoteState> {
  final QuoteRepository repository;

  QuoteBloc({@required this.repository}) : assert(repository != null);

  @override
  QuoteState get initialState => QuoteEmpty();

  @override
  Stream<QuoteState> mapEventToState(QuoteEvent event) async* {
    if (event is FetchQuote) {
      yield QuoteLoading();
      try { …

以下模型类中的以下功能用于什么？

    @override
  String toString() {
    return toJson().toString();
  }

模型类

class User {
  final int id;
  String name, email, token;

  User(this.id, this.name, this.email, this.token);

  User.fromJson(dynamic json) : this.id = json['id'] {
    this.name = json['name'];
    this.email = json['email'];
    this.token = json['token'];
  }

  dynamic toJson() => {'id': id, 'name': name, 'email': email, 'token': token};

  @override
  String toString() {
    return toJson().toString();
  }
}

将flutter项目升级到null-safety时出现如下错误

    The name 'FutureOr' isn't a type, so it can't be used in an 'as' expression.
Try changing the name to the name of an existing type, or creating a type with the name 'FutureOr'