如何使用flowtype绑定异步操作创建者？

Question

我刚刚开始学习flowtype,我需要一些帮助来理解我脑子里不清楚的两件事.

1. 以https://github.com/reactjs/redux/blob/master/examples/todos-flow为例,我想知道如果没有https://github.com/flowtype/flow-的类型定义,对类型的控制是如何工作的键入,在这种情况下:https://github.com/flowtype/flow-typed/blob/master/definitions/npm/redux_v3.xx/flow_v0.33.x-/redux_v3.xxjs？

2. 如果我使用redux定义,bindActionCreators当我尝试绑定异步动作创建器时,验证失败(我正在使用redux-thunk).

使用redux-thunk时如何继续使用flow并绑定异步操作创建器？

代码示例(https://gist.github.com/momsse/323c228e8c5e264067039b8446cd890f):

import { bindActionCreators } from 'redux';
import type { Dispatch } from 'redux';

type Action = { type: 'SET_PROFILE', profile: Object };

/**
 * Based on https://github.com/gaearon/redux-thunk/blob/master/index.d.ts
 */
type ThunkAction = (dispatch: Dispatch<Action>,
                    getState: () => any,
                    extraArgument: any) => any;

type Profile = {
  name: string,
  team: string
}

// Async actions creator
function setProfile(profile: Profile): ThunkAction {
  return dispatch => setTimeout(() => dispatch({ type: 'SET_PROFILE', profile }), 2000);
}

const profileActionCreators = { setProfile };

type Props = {
  actions: {
    setProfile: (profile: Profile) => ThunkAction,
  }
}

function mapDispatchToProps(dispatch: Dispatch<Action>): Props {
  return {
    actions: bindActionCreators(profileActionCreators, dispatch)
  };
}

错误:

 40:     actions: bindActionCreators(profileActionCreators, dispatch)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function call. Function cannot be called on any member of intersection type
 40:     actions: bindActionCreators(profileActionCreators, dispatch)
                  ^^^^^^^^^^^^^^^^^^ intersection
  Member 1:
   49:   declare function bindActionCreators<A, C: ActionCreator<A, any>>(actionCreator: C, dispatch: Dispatch<A>): C;
                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ polymorphic type: function type. See lib: flow-typed/npm/redux_v3.x.x.js:49
  Error:
   49:   declare function bindActionCreators<A, C: ActionCreator<A, any>>(actionCreator: C, dispatch: Dispatch<A>): C;
                                                   ^^^^^^^^^^^^^^^^^^^^^ function type. Callable signature not found in. See lib: flow-typed/npm/redux_v3.x.x.js:49
   40:     actions: bindActionCreators(profileActionCreators, dispatch)
                                       ^^^^^^^^^^^^^^^^^^^^^ object literal
  Member 2:
   50:   declare function bindActionCreators<A, K, C: ActionCreators<K, A>>(actionCreators: C, dispatch: Dispatch<A>): C;
                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ polymorphic type: function type. See lib: flow-typed/npm/redux_v3.x.x.js:50
  Error:
   13:   declare type Dispatch<A: { type: $Subtype<string> }> = (action: A) => A;
                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ property `type` of object type. Property not found in. See lib: flow-typed/npm/redux_v3.x.x.js:13
   21: function setProfile(profile: Profile): ThunkAction {
                                              ^^^^^^^^^^^ function type

Answer 1

这些是 ActionCreator 和 bindActionCreators 的完整声明：

  declare type ActionCreator<A, B> = (...args: Array<B>) => A;
  declare type ActionCreators<K, A> = { [key: K]: ActionCreator<A, any> };

  declare function bindActionCreators<A, C: ActionCreator<A, any>>(actionCreator: C, dispatch: Dispatch<A>): C;
  declare function bindActionCreators<A, K, C: ActionCreators<K, A>>(actionCreators: C, dispatch: Dispatch<A>): C;

在您的代码中，bindActionCreators将 profileActionCreators 的每个属性包装在dispatch. 您似乎期望将调度传递给 setProfile 函数，稍后可以将调度用作回调。

但在我看来，bindActionCreators 并不支持“绑定”调度作为回调。相反，调度是这样“绑定”的：

function bindActionCreator(actionCreator, dispatch) {
  return (...args) => dispatch(actionCreator(...args))
}

所以在你的代码中，它实际上看起来像这样：

function mapDispatchToProps(dispatch: Dispatch<Action>): Props {
  return {
    actions: {
      setProfile: (profile) => dispatch(dispatch => setTimeout(() => dispatch({ type: 'SET_PROFILE', profile }), 2000)),
  };
}

因此，Flowtype 正确地捕获了类型错误，表示 bindActionCreators 期望对象的每个属性都是一个 actionCreator: () => Action。

您可能无法在您的用例中使用bindActionCreators，或者您需要重新考虑如何处理thunk。这是一种应该有效的方法。

const profileActionCreators = { setProfile };

type Props = {
  actions: {
    setProfile: (profile: Profile) => setTimeout,
  }
}

function mapDispatchToProps(dispatch: Dispatch<Action>): Props {
  const boundActions = bindActionCreators(
    profileActionCreators,
    dispatch
  );
  return ({
    actions: {
      setProfile: (profile: Profile) => setTimeout(() => boundActions.setProfile(profile), 2000),
    },
  });
}

thunk 方法

如果您想保留 ThunkAction 方法，您将无法使用 bindActionCreators。这也有效。