dart的泛型和动态有什么区别？ [英] What is the difference between generics and dynamic in dart?

问题描述

让我介绍出现此问题的错误。 （在此处详细说明）

Let me introduce the errors why I got this issue. (Detail here)

type '(String, String) => bool' is not a subtype of type '(dynamic, String) => bool'

这是来自 material_search 和解决方案是：

   - _filter(T v, String c) {
   + _filter(dynamic v, String c) {
   - onSelect: (T value) => Navigator.of(context).pop(value),
   + OnSelect: (dynamic value) => Navigator.of(context).pop(value),

更改所有泛型类型 T 变成动态的，问题似乎在飞镖2出现时发生。

Changing all of generics type T to dynamic, and The issue seems to be happened when dart 2 is appearing.

所以，我在这里遇到了这些问题，

So, I got these question here,

1. 飞镖中的泛型和动态有什么区别？


2. 仅适用于仿制药的限制是什么？在以上问题中，这仅适用于动态。

1. What is the difference between generics and dynamic in dart?
2. What's the limit that only works with generics or on the other hand? In the above issue, this is only works with dynamic.

编辑：
让我提供一个简单的例子来使问题更清楚： p>

用遗传学定义一个类

Let me provide a simple example to make question more clear:

typedef bool GeneticFunction<T>(T geneticData, String key);

class Component<T> extends StatefulWidget {
  Component({this.geneticFunc});
  final GeneticFunction<T> geneticFunc;

  @override
  _componentState<T> createState() => _componentState<T>();
}

一种方法在下面工作

＃1

One of the method is working below

#1

    Component<CoolType>(
      geneticFunc: (CoolType cool, String keyword){
        return false;
      },
    );

＃2

#2

    Component<CoolType>(
      geneticFunc: (dynamic cool, String keyword){
        return false;
      },
    );

＃2 的答案有效，这意味着我甚至不需要通用，只需动态即可。如果您使用＃1 ，有时运行时甚至没有错误，并且可能一整天都呆在那里。

The answer #2 is working, and It means I don't even need generic, just go dynamic. If you use #1, there is sometimes even no error in runtime, and you might stuck at there whole day.

讨论此处，表示 T 在运行时总是动态，因此＃2 是唯一选择。

There is an official discussion here, said that T would always be dynamic in runtime, so #2 is the only choosen.

最后，我不知道何时使用泛型，并且由于上面的结果，现在似乎总是使用动态。

In the conclusion, I have no idea when to use generic, and seems to be always use dynamic now, because of the result above.

推荐答案

很抱歉，我的问题长时间拖延，此问题的真正问题是在StatefulWidget中使用泛型的正确方法是什么？

Sorry for the long delay for my question, the real problem for this issue is What is the correct way to use generic with StatefulWidget?

让我们看一下原始代码：

Let's see the original code:

class Component<T> extends StatefulWidget {
  Component({this.data, this.geneticFunc});
  final T data;
  final GeneticFunction<T> geneticFunc;
  void test()
  {
    var testFunc = geneticFunc;
    testFunc(data, "123");
  }

  @override
  _ComponentState<T> createState() {
    return _ComponentState<T>();
  }
}

class _ComponentState<T> extends State<Component>
{
  @override
  void initState() {
    print("test one");
    var a = widget.geneticFunc;
    print("test two");
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return Container(width: 20, height: 20,);
  }
}

猜猜是什么？只要记住在扩展泛型类时添加< T> ，问题就会变得很复杂。

Guess what? just remember to add a <T> when extending a generic class, and the problem sloved.

class _ComponentState<T> extends State<Component<T>>

所以问题 type‘（String，String）=> bool'不是类型为'（dynamic，String）=>的子类型。 bool'再也不会打扰我了。

So the issue type '(String, String) => bool' is not a subtype of type '(dynamic, String) => bool' will never bother me again.

下面的代码应该可以正常工作了。

And the following code should work now.

Component<CoolType>(
  geneticFunc: (CoolType a, String key){
    return false;
  },
)

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