Thunk方法

Question

我刚刚开始学习flowtype，我需要一些帮助来理解我脑海中不清楚的两件事。

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-typed的类型定义，对类型的控制是如何工作的，在这种情况下：https://github.com/flowtype/flow-typed/blob/master/definitions/npm/redux_v3.x.x/flow_v0.33.x-/redux_v3.x.x.js？
如果我使用redux定义，当我尝试绑定异步动作创建器（我正在使用redux-thunk）时，bindActionCreators的验证失败。

如何在使用redux-thunk时继续使用flow并绑定异步操作创建者？

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将在dispatch中包装profileActionCreators的每个属性。您似乎期望将调度传递给setProfile函数，其中dispatch稍后可以用作回调。

但在我看来，bindActionCreators支持＆＃34;绑定＆＃34;作为回调发送。相反，派遣是＆＃34;绑定＆＃34;像这样：

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

因此，在您的代码中，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正确捕获类型错误，说bindActionCreators期望对象的每个属性都是actionCreator：() => Action。

您可能无法将bindActionCreator用于您的用例，或者您需要重新考虑如何处理thunk。 Here is an approach that should work

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

如果你想保持你的ThunkAction方法，你将无法使用bindActionCreators。 This also works.

如何使用flowtype绑定异步操作创建者？

1 个答案:

Thunk方法