缺少具体的实现"getter平等"/道具问题 [英] Missing concrete implementation 'getter Equatable' / issue with props

问题描述

我正在讨论很多关于blot的教程，其中有些内容扑朔迷离，并且遇到了一些不一致之处.

I am working through many of the tutorials out there on bloc with flutter and running into some inconsistencies.

我正在使用Android Studio，并使用Intellij v1.6.0中的插件来创建块代码.

I am using Android studio and creating the bloc code by using the plugin from Intellij v1.6.0.

对于bloc_event，我继续看到如下示例.

For the bloc_event, I continue to see examples that look like this.

@immutable
abstract class FruitEvent extends Equatable {
  FruitEvent([List props = const []]) : super(props);
}

当我生成bloc文件并查看生成的初始_event时，它看起来像这样.

When I generate my bloc files and look at the initial _event one that generates, it looks like this.

@immutable
abstract class SongEvent extends Equatable {
  const SongEvent();
}

如果我修改生成的代码以包括以下内容...

If I modify my code that is generated to include the following...

[List props = const []]) : super(props)

然后我得到以下错误位置参数过多，预​​期有0个，找到了1个"，该错误在上一行的末尾引用了props.

Then I get the following error "Too many positional arguments, 0 expected, 1 found" which references props at the end of the line shown above.

如果我将代码保留为由bloc插件生成的代码，然后尝试通过添加以下内容来实现我的事件...

If I leave my code as it was generated by the bloc plugin, and then try to implement my events by adding in the following...

class AddSong extends SongEvent {}

然后我得到一个错误:缺少'getter Equatable.props'的具体实现

Then I get an error of "Missing concrete implementation of 'getter Equatable.props'

这是我当前的bloc/song_event.dart

Here is my current bloc/song_event.dart

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

@immutable
abstract class SongEvent extends Equatable {
  const SongEvent();
}

class AddSong extends SongEvent {}

问题我应该使用FuitEvent示例中显示的包含道具的那一行吗?

Question Should I be using the line that has props in it as shown in the FuitEvent example?

我不明白我在这里缺少什么，为什么当我尝试使用与许多教程中所示的方法相同时，它却显示错误.

I don't understand what it is I am missing here and why it shows with an error when I try to use the same method as shown in so many of the tutorials.

推荐答案

相等的覆盖为==和hashCode为您提供服务，因此您不必浪费时间编写大量样板代码.

Equatable overrides == and hashCode for you so you don't have to waste your time writing lots of boilerplate code.

基本上，它有助于对对象进行相等比较.

Basically it helps in doing equality comparison for Objects.

Equatable是一个抽象类，它具有一个吸气剂 List< Object>获取道具； .扩展Equatable的具体类必须重写该getter.

Equatable is an abstract class and it has a getter List<Object> get props;.Concrete Class who extends Equatable must override that getter.

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

@immutable
abstract class SongEvent extends Equatable {
  const SongEvent();
}

class AddSong extends SongEvent {}

在这种情况下，SongEvent是一个抽象类，因此即使扩展了Equatable，也不必实现props getter.但是AddSong是扩展SongEvent并扩展Equatable的具体类，因此AddSong必须在Equatable中实现getter.

In this case, SongEvent is an abstract class, therefore it doesn't have to implement the props getter even tho it extends Equatable. But AddSong is a concrete class that extends SongEvent which extends Equatable, therefore AddSong has to implement the getter in Equatable.

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

@immutable
abstract class SongEvent extends Equatable {
  const SongEvent();
}

// Something like this
class AddSong extends SongEvent {
  final Song song;

  const AddSong(this.song);

  @override
  List<Object> get props => [song];
}

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