[英]Working with Events in F#
我最近问了这个问题: 在F#中重播录制的数据流,并将该代码与我在此处找到的功能的子集相结合: http : //www.mattssoftwareblog.com/?p = 271 ,其组合如下所示:
#r "System.Reactive"
#r "System.CoreEx"
#r "FSharp.PowerPack"
#r "WindowsBase"
#r "PresentationCore"
#r "PresentationFramework"
#r "System.Xaml"
#r "System.Interactive.dll"
open System
open System.Linq
open System.Collections.Generic
open System.Net
open System.IO
open System.Threading
open System.Windows
open System.Windows.Input
open System.Windows.Controls
open System.Windows.Shapes
open System.Windows.Media
open System.Xaml
我需要使用这里生成的事件(来自我之前的SO问题):
let prices = [ (0, 10.0); (1000, 10.5); (500, 9.5); (2500, 8.5); (500, 10.0); (1000, 10.5); (500, 9.5); (2500, 8.5) ]
let evt = new Event<float>()
async { for delay, price in prices do
do! Async.Sleep(delay)
evt.Trigger(price) }
|> Async.StartImmediate
evt.Publish.Add(printfn "Price updated: %A")
用作在这里随机创建的行的数据源(下面的代码来自我提到的博客文章):
let create f =
Observable.Create<_>(fun x ->
f x
new System.Action((fun () -> ())))
let fromEvent (event:IEvent<_,_>) = create (fun x -> event.Add x.OnNext)
// Random Walker
let rand = Random()
let mutable m = 0.
let randomWalker() =
m <- m + (rand.NextDouble() * 10.) - 5.
m
let timer = new System.Timers.Timer()
timer.Interval <- 100.
let timerObs = (timer.Elapsed |> fromEvent).Select(fun _ -> randomWalker())
let chartWindow = new Window(Height = 600., Width = 600.)
let canvas = new Canvas()
chartWindow.Content <- canvas
chartWindow.Show()
let line xs =
let segs =
seq { for x , y in xs |> List.tail ->
LineSegment(Point(x,y), true) :> PathSegment }
let (sx, sy) = xs |> List.head
PathGeometry([PathFigure(Point(sx,sy), segs, false)])
let plot xs (path:Path) =
let now = DateTime.Now
let timeSpan = TimeSpan(0,1,0)
let width = 600.
let height = 600.
let pts = xs |> List.map (fun (x:Timestamped<float>) ->
(600.-(now - (x.Timestamp.DateTime)).TotalMilliseconds * 600. / timeSpan.TotalMilliseconds),x.Value + 300.)
path.Dispatcher.BeginInvoke(new SendOrPostCallback(fun pts -> path.Data <- line (pts :?> (float*float)list)), pts) |> ignore
let trailing (timespan:TimeSpan) (obs:IObservable<'
a>) =
obs.Timestamp()
.Scan([], fun ys x ->
let now = DateTime.Now
let timespan = timespan
x :: (ys |> List.filter (fun x -> (now - x.Timestamp.DateTime) < timespan)))
.Where(fun xs -> xs |> List.length > 1)
// Main Path
let mainPath = new Path(Stroke=Brushes.Blue, StrokeThickness=1.)
canvas.Children.Add(mainPath)
let trailingRandomsSub = (timerObs |> trailing (TimeSpan.FromSeconds(60.))).Subscribe(fun xs -> plot xs mainPath)
timer.Start()
如果将其粘贴到交互式会话中,您将看到一条随机生成的蓝线,而不是使用我的新evt
Event
。 我想我的困惑并不是理解如何制作和使用我的evt
的Observable
。 基本上,我如何让我的蓝线数据源?
提前致谢,
短发
在F#中, IEvent<'T>
接口继承自IObservable<'T>
。 这意味着您可以在任何需要observable的地方使用F#事件。
应用程序的最后一位(接受事件,添加时间戳,使用Scan
获取包含到目前为止生成的项目的列表并绘制进度)可以这样写:
let trailingRandomsSub =
evt.Publish.Timestamp()
|> Observable.scan (fun l e -> e::l) []
|> Observable.add (fun xs -> plot xs mainPath)
F#为某些Rx函数提供了包装器,因此您可以使用Observable.scan
,它具有更多F#友好的语法。 Observable.add
只是Subscribe
另一种语法。
F#事件和observable之间的主要区别在于,当您附加处理程序时,observable会启动。 另一方面,使用Async.StartImmediate
创建的F#事件在Async.StartImmediate
StartImmediate
方法时立即启动(这意味着 - StartImmediate
示例正常工作,您需要一次评估所有内容,或编写启动事件的函数) 。
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