Android foreground Service

MainActivity.fs

namespace ForegroundService

open System
open Android.App
open Android.Util
open Android.Content
open Android.OS
open Android.Runtime
open Android.Views
open Android.Widget
open Android.Support.V4.App
open Android.Support.V4.Content
open Android.Support.V7.App

module Constants = 
    let CHANNEL_ID = "exampleServiceChannel";

[<Application>]
type App(handle:IntPtr, ownerShip:JniHandleOwnership) as this = 
    inherit Application(handle, ownerShip)

    let createNotificationChannel() = 
        if Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.O then
            let serviceChannel = 
                new NotificationChannel(Constants.CHANNEL_ID, "Example Service Channel", Android.App.NotificationImportance.Default)

            let manager = this.GetSystemService(Android.Content.Context.NotificationService) :?> NotificationManager
            manager.CreateNotificationChannel(serviceChannel);

    override this.OnCreate() = 
        base.OnCreate()
        createNotificationChannel();

[<Service()>] 
type ExampleService() = 
    inherit Service() 

    override this.OnBind(intent) = null

    override this.OnStartCommand(intent, flags, startId) = 
        let input = intent.GetStringExtra("inputExtra")

        let activity = typeof<ExampleService>.Assembly |> (fun a -> 
            let activity = intent.GetStringExtra("activity")
            a.GetType(activity))

        let notificationIntent = new Intent(this, activity)
        let pendingIntent = PendingIntent.GetActivity(this, 0, notificationIntent, PendingIntentFlags.OneShot)

        let notification = 
            (new NotificationCompat.Builder(this, Constants.CHANNEL_ID))
                .SetContentTitle("Example Service")
                .SetContentText(input)
                .SetSmallIcon(Resources.Drawable.notification_bg_low)
                .SetContentIntent(pendingIntent)
                .Build();

        this.StartForeground(1, notification);

        //do heavy work on a background thread
        //stopSelf();

        StartCommandResult.NotSticky

[<Activity (Label = "ForegroundService", MainLauncher = true, Icon = "@mipmap/icon")>]
type MainActivity () as this =
    inherit Activity ()
    let TAG = typeof<MainActivity>.ToString()

    let mutable editTextInput:EditText = null

    let startService _ = 
        let input = editTextInput.Text

        let serviceIntent = new Intent(this, typeof<ExampleService>);
        serviceIntent.PutExtra("inputExtra", input) |> ignore
        serviceIntent.PutExtra("activity", typeof<MainActivity>.FullName) |> ignore

        ContextCompat.StartForegroundService (this, serviceIntent)

    let stopService _ =
        new Intent(this, typeof<ExampleService>) |> this.StopService |> ignore

    override this.OnCreate(savedInstanceState) = 
        base.OnCreate(savedInstanceState)

        this.SetContentView Resources.Layout.Main
        editTextInput <- this.FindViewById<EditText>(Resources.Id.edit_text_input)
        let startServiceButton = this.FindViewById<Button>(Resources.Id.startService)
        let stopServiceButton = this.FindViewById<Button>(Resources.Id.stopService)

        startServiceButton.Click.Add startService
        stopServiceButton.Click.Add stopService