How to update binding after validation about elmish.wpf

[awaynemd]

In Elmish.WPF I am using the following code:

"Copay" |> Binding.twoWayOpt((fun m ->Some (Copay.value m.Copay)), SetCopay)
> Binding.addValidation(fun m -> match m with
|{Copay = Copay.InvalidCopay d} -> ["Invalid Copay"]
| _ -> []

Where "Copay" is the bound property to WPF and the model defines Copay as:
Copay: Copay.T

module Copay =
type CopayData = { copay: string}
type T =
| ValidCopay of CopayData
| InvalidCopay of CopayData

    let formatMaskTextBox (s:string) = Regex.Replace( s, @"[^0-9.]","")

    let (|IsCopay|_|) (s:string) = if Regex.IsMatch(s,@"^\d{1,3}.\d{1,2}$") then Some (IsCopay s) else None

    // Define the constructor
    let create (ss: string option) = 
        match ss with
        |None -> InvalidCopay {copay = ""}
        |Some s -> match formatMaskTextBox s with
                   | IsCopay  t -> t |> float |> (fun d -> ValidCopay {copay = sprintf"%3.2f" d})  
                   | _ -> InvalidCopay {copay = s}
        

    // Define deconstructors/ unwrap.  Using "dot" notation to decompose the record.
    let value (f:T) = match f with
                      | ValidCopay d -> d.copay
                      | InvalidCopay d -> d.copay  

    let valueOption (f:T) = match f with
                            | ValidCopay d -> Some d.copay
                            | InvalidCopay d -> None

and SetCopay is:
|SetCopay p -> {m with Copay = Copay.create p}, Cmd.ofMsg InvalidatePolicy

All works correctly to validate an input digital payment. However, the "get" of the binding is executed only once before the
validation code reformats the copay. Hence, the wpf display does not show the "reformatted" input.

Is there anyway to force the binding to update AFTER the validation code is run?

Thanks

[marner2]

Can you format your question better? I'm not seeing your validation code.

To try to answer the question generally, though, remember that Elmish.WPF utilizes an MVU architecture. The View only updates after an Update is applied to the Model. So any updates to the Model that aren't through an Update message will not be seen by the View until some other Update happens (the binding in this case is the View).

[awaynemd]

@marner2 Thank you for your response. I don't see how to reformat the above without copy/paste ? The validation code is being performed with the "match" statement just below the "Copay" binding.

As to your answer, I'm hopeful there is an override (of some sort) that would allow the ".addValidtion" to trigger an update???

[marner2]

Binding.addValidation doesn't actually modify the underlying binding. It sets a parallel error object that WPF error templates can read and display (think of it like an extra bit of information attached to the "CoPay" binding). See Data Validation -> Providing Visual Feedback in the WPF docs about Bindings for more information on how that works.

If you're wanting to modify the actual value in the model so that the "CoPay" binding updates, you would need to do that by modifying the model inside the Update function.