F# asynchronous event handlers for WPF similar to C#'s async and await

Question

How does one code an asynchronous WPF (or Windows Forms) event handler in F#? Specifically, is there any coding pattern that approximates C# 5\'s async and await?

He

Answer 1

Tomas correctly points out that if you can convert the slow method to be asynchronous, then let! and Async.StartImmedate work beautifully. That is preferred.

However, some slow methods do not have asynchronous counterparts. In that case, Tomas's suggestion of Async.AwaitTask works too. For completeness I mention another alternative, manually managing the marshalling with Async.SwitchToContext.

Async.AwaitTask a new Task

let btn_Click (sender : obj) e = 
  let btn = sender :?> Button
  btn.IsEnabled <- false
  async {
    try 
      try 
        let prev = btn.Content :?> int
        let! next = Task.Run(fun () -> incrementSlowly prev) |> Async.AwaitTask
        btn.Content <- next
      with ex -> btn.Content <- ex.Message
    finally
      btn.IsEnabled <- true
  }
  |> Async.StartImmediate

Manually manage thread context

let btn_Click (sender : obj) e = 
  let btn = sender :?> Button
  btn.IsEnabled <- false
  let prev = btn.Content :?> int
  let uiContext = SynchronizationContext.Current
  async {
    try
      try
        let next = incrementSlowly prev
        do! Async.SwitchToContext uiContext
        btn.Content <- next
      with ex ->
        do! Async.SwitchToContext uiContext
        btn.Content <- ex.Message
    finally
      btn.IsEnabled <- true
  }
  |> Async.Start