事件

事件

事件允许类在彼此之间发送和接收消息。

在GUI中，事件是用户动作，例如按键，点击，鼠标移动等，或者像系统生成的通知的某些事件。 应用程序需要在事件发生时对其进行响应。 例如，中断。 事件用于进程间通信。

对象通过同步消息传递彼此通信。

事件附加到其他功能; 对象将回调函数注册到事件，并且这些回调在（和if）事件由某个对象触发时执行。

事件类和事件模块

Control.Event 类有助于创建可观察的对象或事件。
它有以下函数来处理事件

该Control.Event模块提供了一个管理事件流功能

创建事件

创建事件，并通过Event类使用。事件构造函数用于创建一个事件。

例

type Worker(name : string, shift : string) =
   let mutable _name = name;
   let mutable _shift = shift;
   let nameChanged = new Event<unit>() (* creates event *)
   let shiftChanged = new Event<unit>() (* creates event *)

   member this.Name
      with get() = _name
      and set(value) = _name <- value

   member this.Shift
      with get() = _shift
      and set(value) = _shift <- value

之后，您需要将nameChanged字段公开为公共函数，以便监听器可以挂钩到要使用事件的Publish属性的事件。

type Worker(name : string, shift : string) =
   let mutable _name = name;
   let mutable _shift = shift;

   let nameChanged = new Event<unit>() (* creates event *)
   let shiftChanged = new Event<unit>() (* creates event *)

   member this.NameChanged = nameChanged.Publish (* exposed event handler *)
   member this.ShiftChanged = shiftChanged.Publish (* exposed event handler *)

   member this.Name
      with get() = _name
      and set(value) = _name <- value
      nameChanged.Trigger() (* invokes event handler *)

   member this.Shift
      with get() = _shift
      and set(value) = _shift <- value
   shiftChanged.Trigger() (* invokes event handler *)

接下来，添加回调事件处理程序。每个事件处理程序的类型IEvent <'T>，它提供了几种方法

以下部分提供了一个完整的例子。

例

下面的示例演示的概念和技术上面讨论

type Worker(name : string, shift : string) =
   let mutable _name = name;
   let mutable _shift = shift;

   let nameChanged = new Event<unit>() (* creates event *)
   let shiftChanged = new Event<unit>() (* creates event *)

   member this.NameChanged = nameChanged.Publish (* exposed event handler *)
   member this.ShiftChanged = shiftChanged.Publish (* exposed event handler *)

   member this.Name
      with get() = _name
      and set(value) = 
         _name <- value
         nameChanged.Trigger() (* invokes event handler *)

   member this.Shift
      with get() = _shift
      and set(value) = 
         _shift <- value
         shiftChanged.Trigger() (* invokes event handler *)

let wk = new Worker("Wilson", "Evening")
wk.NameChanged.Add(fun () -> printfn "Worker changed name! New name: %s" wk.Name)
wk.Name <- "William"
wk.NameChanged.Add(fun () -> printfn "-- Another handler attached to NameChanged!")
wk.Name <- "Bill"

wk.ShiftChanged.Add(fun () -> printfn "Worker changed shift! New shift: %s" wk.Shift)
wk.Shift <- "Morning"
wk.ShiftChanged.Add(fun () -> printfn "-- Another handler attached to ShiftChanged!")
wk.Shift <- "Night"

当你编译和执行程序，它产生以下输出

Worker changed name! New name: William
Worker changed name! New name: Bill
-- Another handler attached to NameChanged!
Worker changed shift! New shift: Morning
Worker changed shift! New shift: Night
-- Another handler attached to ShiftChanged!