Android button like FB chat bubble

MainActivity.fs

namespace UILearning

open System

open Android.App
open Android.Content
open Android.OS
open Android.Runtime
open Android.Views
open Android.Widget
open Android.Graphics

[<Service>]
type UIService() =
  inherit Service()
  let mutable count:int = 1
  override __.OnBind(intent:Intent) =
    base.OnBind intent
//  member OnCreate : unit -> unit
//  member OnDestroy : unit -> unit
  override __.OnStart(intent:Intent,startId:int) =
    let param=new WindowManagerLayoutParams()
    param.Flags <- WindowManagerFlags.NotFocusable
    let view = new Button(__)
    view.LayoutParameters <- new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WrapContent, RelativeLayout.LayoutParams.WrapContent)
    view.SetBackgroundColor(Color.Red)
    view.Text <- "Notif !"
    let parent = view.Parent :?> ViewGroup
    if parent <> null
    then
      parent.RemoveView view
    param.Format <- Format.Rgba8888
    param.Type <- WindowManagerTypes.SystemAlert
    param.Gravity <- GravityFlags.Bottom ||| GravityFlags.Right
    param.Width <- 
      if parent <> null
      then WindowManagerLayoutParams.WrapContent
      else view.LayoutParameters.Width
    param.Height <- 
      if parent <> null
      then WindowManagerLayoutParams.WrapContent
      else view.LayoutParameters.Height
    let windowManager =
      __.ApplicationContext.GetSystemService(Context.WindowService).JavaCast<IWindowManager>()
    windowManager.AddView(view, param)
    view.Click.Add(fun _ ->
      view.Text <- sprintf "%d clicks!" count
      count <- count + 1
    )
    ()

// http://stackoverflow.com/questions/4481226/creating-a-system-overlay-window-always-on-top
[<Activity (Label = "UILearning", MainLauncher = true)>]
type MainActivity () =
    inherit Activity ()

    let mutable count:int = 1

    override __.OnCreate (bundle) =
        base.OnCreate (bundle)
        __.SetContentView (Resource_Layout.Main)
        let button = __.FindViewById<Button>(Resource_Id.MyButton)
        button.Click.Add (fun _ -> 
            button.Text <- sprintf "%d clicks!" count
            count <- count + 1
            let t = typeof<UIService>
            let intent = new Intent(__, t)
            __.StartService intent |> ignore
        )