Saving and Restoring app state

Application state is very simple to save by serializing the model into app.Properties. For example, you can store as JSON as follows using Json.NET:
type Application() =
let modelId = "model"
override __.OnSleep() =
let json = Newtonsoft.Json.JsonConvert.SerializeObject(runner.CurrentModel)
Debug.WriteLine("OnSleep: saving model into app.Properties, json = {0}", json)
app.Properties.[modelId] <- json
override __.OnResume() =
Debug.WriteLine "OnResume: checking for model in app.Properties"
match app.Properties.TryGetValue modelId with
| true, (:? string as json) ->
Debug.WriteLine("OnResume: restoring model from app.Properties, json = {0}", json)
let model = Newtonsoft.Json.JsonConvert.DeserializeObject<App.Model>(json)
Debug.WriteLine("OnResume: restoring model from app.Properties, model = {0}", (sprintf "%0A" model))
runner.SetCurrentModel (model, Cmd.none)
| _ -> ()
with ex ->
App.program.onError("Error while restoring model found in app.Properties", ex)
override this.OnStart() =
Debug.WriteLine "OnStart: using same logic as OnResume()"