WinForms + Async

gistfile1.fs

open System
open System.Net
open Microsoft.FSharp.Control.WebExtensions
open System.Windows.Forms
open System.Threading
 
let form = new Form()
let text = new Label()
let button = new Button()
 
let urlList = [ "Microsoft.com", "http://www.microsoft.com/"
                "MSDN", "http://msdn.microsoft.com/"
                "Bing", "http://www.bing.com"
              ]
 
let fetchAsync(name, url:string, ctx) =
    async {
        try
            let uri = new System.Uri(url)
            let webClient = new WebClient()
            let! html = webClient.AsyncDownloadString(uri)
            do! Async.SwitchToContext ctx
            text.Text <- sprintf "Read %d characters for %s" html.Length name
        with
            | ex -> printfn "%s" (ex.Message);
    }
 
let runAll() =
    let ctx = SynchronizationContext.Current
    urlList
    |> Seq.map (fun(site, url) -> fetchAsync(site, url, ctx))
    |> Async.Parallel
    |> Async.Ignore
    |> Async.Start
 
form.Width  <- 400
form.Height <- 300
form.Visible <- true
form.Text <- "Test download tool"
 
text.Width <- 200
text.Height <- 50
text.Top <- 0
text.Left <- 0
form.Controls.Add(text)
 
button.Text <- "click me"
button.Top <- text.Height
button.Left <- 0
button.Click |> Event.add(fun sender -> runAll() |> ignore)
form.Controls.Add(button)
 
[<STAThread>]
do Application.Run(form)