事件

原文：https://gobuffalo.io/documentation/guides/events/

Events 事件

Since 0.13.0-beta.2 自 0.13.0-beta.2 起

The events package allows for Go applications, including Buffalo applications, to listen, and emit, global event messages.

​ 事件包允许 Go 应用程序（包括 Buffalo 应用程序）监听和发出全局事件消息。

Listening for Events 监听事件

To start listening for events a events#Listener must first be registered with the events package.

​ 要开始监听事件，必须先将 events#Listener 注册到事件包中。

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func init() {
  _, err := events.Listen(func(e events.Event) {
    // do work
  })
}

Once registered this new listener function will be sent all events emitted through the events package.

​ 注册后，此新侦听器函数将被发送通过事件包发出的所有事件。

Emitting Events 发出事件

When emitting events the Kind attribute should be a unique, but constant, string. It is this attribute that users will use to determine how to respond to events they receive.

​ 发出事件时， Kind 属性应为唯一但不变的字符串。用户将使用此属性来确定如何响应他们收到的事件。

It is recommended to namespace this attribute like such, with error events being suffixed with :err.

​ 建议像这样对该属性进行命名空间，错误事件以 :err 结尾。

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"<package-name>:<additional-names>:<optional-error>"
"myapp:foo:start"
"myapp:foo:stop"
"mypkg:workers:bar:err"

This naming pattern makes it easier for users to filter events to only those that they care about. See Filtering Events for more details.

​ 这种命名模式使用户可以更轻松地将事件筛选为仅他们关心的事件。有关更多详细信息，请参阅筛选事件。

There are multiple ways to emit an events#Event in your Go code. The events#EmitError and events#EmitPayload functions both accept a payload interface{} argument. It is recommended to use events#Payload for payloads; any other type passed in will get converted into a events#Payload with the argument set in the payload with the key, data.

​ 在 Go 代码中有多种方式可以发出 events#Event。events#EmitError 和 events#EmitPayload 函数都接受 payload interface{} 参数。建议对有效负载使用 events#Payload；传入的任何其他类型都将转换为 events#Payload，其中参数在有效负载中设置，键为 data 。

• events#Emit

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func MyHandler(c buffalo.Context) error {
  e := events.Event{
    Kind:    "coke:myhandler:hello",
    Message: "hi!",
    Payload: events.Payload{"context": c},
  }
  if err := events.Emit(e); err != nil {
    return err
  }
  return c.Render(200, r.HTML("index.html"))
}

• events#EmitError

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func MyHandler(c buffalo.Context) error {
  if err := events.EmitError("coke:myhandler:hello:err", errors.New("boom"), c); err != nil {
    return err
  }
  return c.Render(200, r.HTML("index.html"))
}

• events#EmitPayload

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func MyHandler(c buffalo.Context) error {
  p := events.Payload{
    "message": "hi!",
  }
  if err := events.EmitPayload("coke:myhandler:hello", p); err != nil {
    return err
  }
  return c.Render(200, r.HTML("index.html"))
}

Filtering Events 筛选事件

In the Emitting Events section the naming convention for events#Event.Kind is described. By the checking the value of events#Event.Kind.

​ 在发出事件部分中，描述了 events#Event.Kind 的命名约定。通过检查 events#Event.Kind 的值。

direct match 直接匹配

matching with a switch statement 使用 switch 语句进行匹配

matching error events 匹配错误事件

matching on prefix 匹配前缀

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// direct match
events.Listen(func(e events.Event) {
  if e.Kind != buffalo.EvtRouteStarted {
    // do nothing
    return
  }
  // do work on the route event
})

Stop Listening for Events 停止监听事件

When registering a new events#Listener a events#DeleteFn is returned. This function should be held on to and used when you want to remove the added listener.

​ 注册新的 events#Listener 时，会返回一个 events#DeleteFn。当您想要移除已添加的监听器时，应保留此函数并使用它。

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deleteFn, err := events.Listen(func(e events.Event) {
  // do work
})
if err != nil {
  return err
}
defer deleteFn()

Listening with Plugins 使用插件进行监听

To enable a plugin to a receive a JSON version of emitted events, the plugin can set the events#Command.BuffaloCommand value to events when listing the available commands for the plugin.

​ 为了使插件能够接收已发送事件的 JSON 版本，该插件可以在列出插件的 available 命令时将 events#Command.BuffaloCommand 值设置为 events 。

availableCmd

listenCmd

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// availableCmd
var availableCmd = &cobra.Command{
  Use:   "available",
  Short: "a list of available buffalo plugins",
  RunE: func(cmd *cobra.Command, args []string) error {
    plugs := plugins.Commands{
      {Name: "listen", UseCommand: "listen", BuffaloCommand: "events", Description: listenCmd.Short, Aliases: listenCmd.Aliases},
    }
    return json.NewEncoder(os.Stdout).Encode(plugs)
  },
}

Integrating a Messaging Queue 集成消息队列

It is often desirable to take events emitted and send them to a message queue, such as Kafka or Redis, to be processed externally. The events package does not have a directhook for this sort of functionality, the most direct way of enabling this behavior is to register a events#Listener that can then hand the event over to the appropriate message queue.

​ 通常需要获取已发送的事件并将它们发送到消息队列（例如 Kafka 或 Redis）以供外部处理。events 包没有针对此类功能的直接挂钩，启用此行为的最直接方法是注册一个 events#Listener，然后该监听器可以将事件交给相应的消息队列。

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events.Listen(func(e events.Event) {
  myMessageQ.DoWork(e)
})

Known Events 已知事件

Application Events 应用程序事件

The following events are known to be emitted by Buffalo during the application lifecyle.

​ 已知 Buffalo 在应用程序生命周期期间会发出以下事件。

Buffalo Dev Events Buffalo Dev 事件

The following events are known to be emitted by the buffalo dev during the development lifecyle.

​ 已知以下事件在开发生命周期期间由 buffalo dev 发出。