如何使用超时调度Redux操作？ [英] How to dispatch a Redux action with a timeout?

问题描述

我有一个更新应用程序通知状态的操作。通常，此通知将是某种错误或信息。我需要在5秒后发送另一个操作，将通知状态返回到初始状态，因此不会发出通知。这背后的主要原因是提供通知在5秒后自动消失的功能。

I have an action that updates notification state of my application. Usually, this notification will be an error or info of some sort. I need to then dispatch another action after 5 seconds that will return the notification state to initial one, so no notification. The main reason behind this is to provide functionality where notifications disappear automatically after 5 seconds.

我没有运气使用 setTimeout 并返回另一个动作，但无法找到如何在线完成。所以欢迎任何建议。

I had no luck with using setTimeout and returning another action and can't find how this is done online. So any advice is welcome.

推荐答案

不要落入思考图书馆的陷阱应该规定如何做所有事情。如果您想在JavaScript中执行超时操作，则需要使用 setTimeout 。没有理由认为Redux操作应该有任何不同。

Don’t fall into the trap of thinking a library should prescribe how to do everything. If you want to do something with a timeout in JavaScript, you need to use setTimeout. There is no reason why Redux actions should be any different.

Redux 提供了一些处理异步内容的替代方法，但是你应该只做当你意识到重复太多代码时使用它们。除非你有这个问题，否则请使用语言提供的内容并选择最简单的解决方案。

Redux does offer some alternative ways of dealing with asynchronous stuff, but you should only use those when you realize you are repeating too much code. Unless you have this problem, use what the language offers and go for the simplest solution.

这是迄今为止最简单的方法。这里没有Redux的特定内容。

This is by far the simplest way. And there’s nothing specific to Redux here.

store.dispatch({ type: 'SHOW_NOTIFICATION', text: 'You logged in.' })
setTimeout(() => {
  store.dispatch({ type: 'HIDE_NOTIFICATION' })
}, 5000)

同样，来自连接组件内部：

Similarly, from inside a connected component:

this.props.dispatch({ type: 'SHOW_NOTIFICATION', text: 'You logged in.' })
setTimeout(() => {
  this.props.dispatch({ type: 'HIDE_NOTIFICATION' })
}, 5000)

唯一的区别是在连接的组件中你通常无法访问商店本身，但获得 dispatch（）或作为道具注入的特定动作创建者。但是这对我们没有任何影响。

The only difference is that in a connected component you usually don’t have access to the store itself, but get either dispatch() or specific action creators injected as props. However this doesn’t make any difference for us.

如果您不喜欢在从不同组件调度相同的操作时输入拼写错误，您可能想要提取动作创建者而不是内联调度操作对象：

If you don’t like making typos when dispatching the same actions from different components, you might want to extract action creators instead of dispatching action objects inline:

// actions.js
export function showNotification(text) {
  return { type: 'SHOW_NOTIFICATION', text }
}
export function hideNotification() {
  return { type: 'HIDE_NOTIFICATION' }
}

// component.js
import { showNotification, hideNotification } from '../actions'

this.props.dispatch(showNotification('You just logged in.'))
setTimeout(() => {
  this.props.dispatch(hideNotification())
}, 5000)

或者，如果您之前使用连接它们，则连接（）：

Or, if you have previously bound them with connect():

this.props.showNotification('You just logged in.')
setTimeout(() => {
  this.props.hideNotification()
}, 5000)

到目前为止，我们还没有使用任何中间件或其他先进的理念。

So far we have not used any middleware or other advanced concept.

上述方法在简单的情况下工作正常，但您可能会发现它有一个几个问题：

The approach above works fine in simple cases but you might find that it has a few problems:

• 它会强制您在想要显示通知的任何地方复制此逻辑。


• 通知没有ID，因此如果您足够快地显示两个通知，则会出现竞争条件。当第一个超时结束时，它将发送 HIDE_NOTIFICATION ，错误地在超时后错误地隐藏第二个通知。

• It forces you to duplicate this logic anywhere you want to show a notification.
• The notifications have no IDs so you’ll have a race condition if you show two notifications fast enough. When the first timeout finishes, it will dispatch HIDE_NOTIFICATION, erroneously hiding the second notification sooner than after the timeout.

要解决这些问题，您需要提取一个集中超时逻辑并调度这两个操作的函数。它可能如下所示：

To solve these problems, you would need to extract a function that centralizes the timeout logic and dispatches those two actions. It might look like this:

// actions.js
function showNotification(id, text) {
  return { type: 'SHOW_NOTIFICATION', id, text }
}
function hideNotification(id) {
  return { type: 'HIDE_NOTIFICATION', id }
}

let nextNotificationId = 0
export function showNotificationWithTimeout(dispatch, text) {
  // Assigning IDs to notifications lets reducer ignore HIDE_NOTIFICATION
  // for the notification that is not currently visible.
  // Alternatively, we could store the timeout ID and call
  // clearTimeout(), but we’d still want to do it in a single place.
  const id = nextNotificationId++
  dispatch(showNotification(id, text))

  setTimeout(() => {
    dispatch(hideNotification(id))
  }, 5000)
}

现在组件可以使用 showNotificationWithTimeout 不重复此逻辑或具有不同通知的竞争条件：

Now components can use showNotificationWithTimeout without duplicating this logic or having race conditions with different notifications:

// component.js
showNotificationWithTimeout(this.props.dispatch, 'You just logged in.')

// otherComponent.js
showNotificationWithTimeout(this.props.dispatch, 'You just logged out.')    

为什么 showNotificationWithTimeout（）接受派遣作为第一个参数？因为它需要将操作分派给商店。通常，组件可以访问 dispatch ，但由于我们希望外部函数控制调度，我们需要让它控制调度。

Why does showNotificationWithTimeout() accept dispatch as the first argument? Because it needs to dispatch actions to the store. Normally a component has access to dispatch but since we want an external function to take control over dispatching, we need to give it control over dispatching.

如果你有一个单件商店从某个模块导出，你可以直接导入它，然后直接在它上面输入 dispatch ：

If you had a singleton store exported from some module, you could just import it and dispatch directly on it instead:

// store.js
export default createStore(reducer)

// actions.js
import store from './store'

// ...

let nextNotificationId = 0
export function showNotificationWithTimeout(text) {
  const id = nextNotificationId++
  store.dispatch(showNotification(id, text))

  setTimeout(() => {
    store.dispatch(hideNotification(id))
  }, 5000)
}

// component.js
showNotificationWithTimeout('You just logged in.')

// otherComponent.js
showNotificationWithTimeout('You just logged out.')    

这看起来更简单但我们不推荐这种方法。我们不喜欢它的主要原因是因为它迫使商店成为单身人士。这使得实现服务器呈现变得非常困难。在服务器上，您将希望每个请求都有自己的存储，以便不同的用户获得不同的预加载数据。

This looks simpler but we don’t recommend this approach. The main reason we dislike it is because it forces store to be a singleton. This makes it very hard to implement server rendering. On the server, you will want each request to have its own store, so that different users get different preloaded data.

单身商店也使测试更加困难。在测试动作创建者时，您不能再模拟商店，因为它们引用从特定模块导出的特定实体商店。您甚至无法从外部重置其状态。

A singleton store also makes testing harder. You can no longer mock a store when testing action creators because they reference a specific real store exported from a specific module. You can’t even reset its state from outside.

因此，虽然您在技术上可以从模块导出单件商店，但我们不鼓励它。除非您确定您的应用永远不会添加服务器呈现，否则请不要这样做。

So while you technically can export a singleton store from a module, we discourage it. Don’t do this unless you are sure that your app will never add server rendering.

返回上一版本：

// actions.js

// ...

let nextNotificationId = 0
export function showNotificationWithTimeout(dispatch, text) {
  const id = nextNotificationId++
  dispatch(showNotification(id, text))

  setTimeout(() => {
    dispatch(hideNotification(id))
  }, 5000)
}

// component.js
showNotificationWithTimeout(this.props.dispatch, 'You just logged in.')

// otherComponent.js
showNotificationWithTimeout(this.props.dispatch, 'You just logged out.')    

这解决了重复逻辑的问题，并使我们免于竞争条件。

This solves the problems with duplication of logic and saves us from race conditions.

对于简单的应用程序，该方法应该足够了。如果您对它感到满意，请不要担心中间件。

For simple apps, the approach should suffice. Don’t worry about middleware if you’re happy with it.

但是，在较大的应用程序中，您可能会发现一些不便之处。

In larger apps, however, you might find certain inconveniences around it.

例如，我们不得不传递 dispatch 。这使得分离容器和表示组件变得更加棘手，因为任何组件都是如此以上述方式异步调度Redux操作必须接受 dispatch 作为prop，以便它可以进一步传递它。你不能再将动作创建者绑定到 connect（），因为 showNotificationWithTimeout（）并不是真正的动作创建者。它不会返回Redux动作。

For example, it seems unfortunate that we have to pass dispatch around. This makes it trickier to separate container and presentational components because any component that dispatches Redux actions asynchronously in the manner above has to accept dispatch as a prop so it can pass it further. You can’t just bind action creators with connect() anymore because showNotificationWithTimeout() is not really an action creator. It does not return a Redux action.

此外，要记住哪些函数是同步动作创建者，如 showNotification（）和哪些是异步助手，如 showNotificationWithTimeout（）。你必须以不同的方式使用它们，并注意不要互相误解。

In addition, it can be awkward to remember which functions are synchronous action creators like showNotification() and which are asynchronous helpers like showNotificationWithTimeout(). You have to use them differently and be careful not to mistake them with each other.

这是找到一种方法合法化这种模式的动机将 dispatch 提供给辅助函数，并帮助Redux看到这样的异步动作创建者作为普通动作创建者的特例而不是完全不同的函数。

This was the motivation for finding a way to "legitimize" this pattern of providing dispatch to a helper function, and help Redux "see" such asynchronous action creators as a special case of normal action creators rather than totally different functions.

如果你还在我们身边并且你也认为你的应用程序存在问题，欢迎你使用 Redux Thunk 中间件。

If you’re still with us and you also recognize as a problem in your app, you are welcome to use the Redux Thunk middleware.

在一个要点中，Redux Thunk教Redux识别特殊类型的行为实际上是函数：

In a gist, Redux Thunk teaches Redux to recognize special kinds of actions that are in fact functions:

import { createStore, applyMiddleware } from 'redux'
import thunk from 'redux-thunk'

const store = createStore(
  reducer,
  applyMiddleware(thunk)
)

// It still recognizes plain object actions
store.dispatch({ type: 'INCREMENT' })

// But with thunk middleware, it also recognizes functions
store.dispatch(function (dispatch) {
  // ... which themselves may dispatch many times
  dispatch({ type: 'INCREMENT' })
  dispatch({ type: 'INCREMENT' })
  dispatch({ type: 'INCREMENT' })

  setTimeout(() => {
    // ... even asynchronously!
    dispatch({ type: 'DECREMENT' })
  }, 1000)
})

启用此中间件后，如果您调度函数，Redux Thunk中间件会将 dispatch 作为参数。它也会吞下这样的动作，所以不要担心你的减速器接收奇怪的函数参数。你的Reducer只接收普通的对象动作 - 直接发射，或者由我们刚才描述的函数发出。

When this middleware is enabled, if you dispatch a function, Redux Thunk middleware will give it dispatch as an argument. It will also "swallow" such actions so don’t worry about your reducers receiving weird function arguments. Your reducers will only receive plain object actions—either emitted directly, or emitted by the functions as we just described.

这看起来不是很有用，是吗？不是在这种特殊情况下。但是它允许我们声明 showNotificationWithTimeout（）作为常规Redux动作创建者：

This does not look very useful, does it? Not in this particular situation. However it lets us declare showNotificationWithTimeout() as a regular Redux action creator:

// actions.js
function showNotification(id, text) {
  return { type: 'SHOW_NOTIFICATION', id, text }
}
function hideNotification(id) {
  return { type: 'HIDE_NOTIFICATION', id }
}

let nextNotificationId = 0
export function showNotificationWithTimeout(text) {
  return function (dispatch) {
    const id = nextNotificationId++
    dispatch(showNotification(id, text))

    setTimeout(() => {
      dispatch(hideNotification(id))
    }, 5000)
  }
}

注意如何函数几乎与我们在上一节中写的相同。但是它不接受 dispatch 作为第一个参数。相反，返回一个接受 dispatch 作为第一个参数的函数。

Note how the function is almost identical to the one we wrote in the previous section. However it doesn’t accept dispatch as the first argument. Instead it returns a function that accepts dispatch as the first argument.

如何我们在组件中使用它？当然，我们可以这样写：

How would we use it in our component? Definitely, we could write this:

// component.js
showNotificationWithTimeout('You just logged in.')(this.props.dispatch)

我们正在调用异步动作创建器来获取想要的内部函数只需派遣，然后我们传递派遣。

We are calling the async action creator to get the inner function that wants just dispatch, and then we pass dispatch.

然而，这比原始版本更加尴尬！为什么我们甚至走那条路？

However this is even more awkward than the original version! Why did we even go that way?

因为我之前告诉你的。 如果启用了Redux Thunk中间件，那么每当您尝试调度函数而不是操作对象时，中间件将使用 dispatch 方法本身作为第一个调用该函数参数。

Because of what I told you before. If Redux Thunk middleware is enabled, any time you attempt to dispatch a function instead of an action object, the middleware will call that function with dispatch method itself as the first argument.

所以我们可以这样做：

// component.js
this.props.dispatch(showNotificationWithTimeout('You just logged in.'))

最后，调度异步操作（实际上是一系列操作）与将同一个操作同步分派给组件没什么不同。这是好事，因为组件不应该关心某些事情是同步发生还是异步发生。我们只是抽象出来。

Finally, dispatching an asynchronous action (really, a series of actions) looks no different than dispatching a single action synchronously to the component. Which is good because components shouldn’t care whether something happens synchronously or asynchronously. We just abstracted that away.

请注意，因为我们教导Redux识别出这样的特殊动作创建者（我们称之为 thunk 动作创建者），我们现在可以在任何我们使用常规动作创建者的地方使用它们。例如，我们可以使用 connect（）：

Notice that since we "taught" Redux to recognize such "special" action creators (we call them thunk action creators), we can now use them in any place where we would use regular action creators. For example, we can use them with connect():

// actions.js

function showNotification(id, text) {
  return { type: 'SHOW_NOTIFICATION', id, text }
}
function hideNotification(id) {
  return { type: 'HIDE_NOTIFICATION', id }
}

let nextNotificationId = 0
export function showNotificationWithTimeout(text) {
  return function (dispatch) {
    const id = nextNotificationId++
    dispatch(showNotification(id, text))

    setTimeout(() => {
      dispatch(hideNotification(id))
    }, 5000)
  }
}

// component.js

import { connect } from 'react-redux'

// ...

this.props.showNotificationWithTimeout('You just logged in.')

// ...

export default connect(
  mapStateToProps,
  { showNotificationWithTimeout }
)(MyComponent)

阅读状态在Thunks中

通常，您的Reducer包含用于确定下一个状态的业务逻辑。但是，只有在调度动作后才会启动减速器。如果你在thunk动作创建者中有副作用（例如调用API），并且你想在某些条件下阻止它，该怎么办？

Reading State in Thunks

Usually your reducers contain the business logic for determining the next state. However, reducers only kick in after the actions are dispatched. What if you have a side effect (such as calling an API) in a thunk action creator, and you want to prevent it under some condition?

不使用thunk中间件，你只需在组件内部进行检查：

Without using the thunk middleware, you’d just do this check inside the component:

// component.js
if (this.props.areNotificationsEnabled) {
  showNotificationWithTimeout(this.props.dispatch, 'You just logged in.')
}

然而，提取动作创建者的目的是将这种重复逻辑集中在许多组件上。幸运的是，Redux Thunk为您提供了一种读取 Redux商店当前状态的方法。除了 dispatch 之外，它还传递 getState 作为从thunk动作创建者返回的函数的第二个参数。这让thunk读取商店的当前状态。

However, the point of extracting an action creator was to centralize this repetitive logic across many components. Fortunately, Redux Thunk offers you a way to read the current state of the Redux store. In addition to dispatch, it also passes getState as the second argument to the function you return from your thunk action creator. This lets the thunk read the current state of the store.

let nextNotificationId = 0
export function showNotificationWithTimeout(text) {
  return function (dispatch, getState) {
    // Unlike in a regular action creator, we can exit early in a thunk
    // Redux doesn’t care about its return value (or lack of it)
    if (!getState().areNotificationsEnabled) {
      return
    }

    const id = nextNotificationId++
    dispatch(showNotification(id, text))

    setTimeout(() => {
      dispatch(hideNotification(id))
    }, 5000)
  }
}

不要滥用这种模式。当有缓存数据可用时，它可以避免API调用，但它不是构建业务逻辑的良好基础。如果您仅使用 getState（）来有条件地分派不同的操作，请考虑将业务逻辑放入reducers中。

Don’t abuse this pattern. It is good for bailing out of API calls when there is cached data available, but it is not a very good foundation to build your business logic upon. If you use getState() only to conditionally dispatch different actions, consider putting the business logic into the reducers instead.

现在您对thunks的工作方式有了基本的直觉，请查看Redux 异步示例。

Now that you have a basic intuition about how thunks work, check out Redux async example which uses them.

您可能会发现许多thunk返回Promises的示例。这不是必需的，但可以非常方便。 Redux不关心你从thunk返回什么，但是它从 dispatch（）中获得它的返回值。这就是为什么你可以通过调用 dispatch（someThunkReturningPromise（））来返回一个Promise并等待它完成。然后（...）。

You may find many examples in which thunks return Promises. This is not required but can be very convenient. Redux doesn’t care what you return from a thunk, but it gives you its return value from dispatch(). This is why you can return a Promise from a thunk and wait for it to complete by calling dispatch(someThunkReturningPromise()).then(...).

您也可以将复杂的thunk动作创建者分成几个较小的thunk动作创建者。 thunks提供的 dispatch 方法本身可以接受thunk，因此您可以递归地应用该模式。同样，这对Promise最有效，因为你可以在其上实现异步控制流。

You may also split complex thunk action creators into several smaller thunk action creators. The dispatch method provided by thunks can accept thunks itself, so you can apply the pattern recursively. Again, this works best with Promises because you can implement asynchronous control flow on top of that.

对于某些应用程序，您可能会发现自己处于异步控制流的情况要求太复杂，无法用thunk表达。例如，重试失败的请求，带令牌的重新授权流程或逐步入门可能过于冗长且以这种方式编写时容易出错。在这种情况下，您可能希望查看更高级的异步控制流解决方案，例如 Redux Saga 或 Redux Loop 。评估它们，比较与您的需求相关的示例，并选择您最喜欢的那个。

For some apps, you may find yourself in a situation where your asynchronous control flow requirements are too complex to be expressed with thunks. For example, retrying failed requests, reauthorization flow with tokens, or a step-by-step onboarding can be too verbose and error-prone when written this way. In this case, you might want to look at more advanced asynchronous control flow solutions such as Redux Saga or Redux Loop. Evaluate them, compare the examples relevant to your needs, and pick the one you like the most.

最后，如果你不这样做，请不要使用任何东西（包括thunk）他们真正需要他们。请记住，根据要求，您的解决方案可能看起来很简单

Finally, don’t use anything (including thunks) if you don’t have the genuine need for them. Remember that, depending on the requirements, your solution might look as simple as

store.dispatch({ type: 'SHOW_NOTIFICATION', text: 'You logged in.' })
setTimeout(() => {
  store.dispatch({ type: 'HIDE_NOTIFICATION' })
}, 5000)

除非你知道为什么要这样做，否则不要出汗。

Don’t sweat it unless you know why you’re doing this.

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