From d0d1eb1ed2a2a6a1d2b27fcafbd3785cf9e6d6c2 Mon Sep 17 00:00:00 2001
From: Joshua Marner <biz@jmarner.com>
Date: Fri, 4 Nov 2022 22:23:57 -0500
Subject: [PATCH] Fix bug with events getting raised too soon

---
 src/Elmish.WPF/DynamicViewModel.fs | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/Elmish.WPF/DynamicViewModel.fs b/src/Elmish.WPF/DynamicViewModel.fs
index 31a2493e..be723315 100644
--- a/src/Elmish.WPF/DynamicViewModel.fs
+++ b/src/Elmish.WPF/DynamicViewModel.fs
@@ -77,7 +77,12 @@ module internal ViewModelHelper =
     ErrorsChanged = DelegateEvent<EventHandler<DataErrorsChangedEventArgs>>()
   }
 
-  let updateModel newModel helper =
+  let getEventsToRaise newModel helper =
+    helper.Bindings
+      |> Seq.collect (fun (Kvp (name, binding)) -> Update(helper.LoggingArgs, name).Recursive(helper.Model, newModel, binding))
+      |> Seq.toList
+
+  let raiseEvents eventsToRaise helper =
     let {
       log = log
       nameChain = nameChain } = helper.LoggingArgs
@@ -90,19 +95,13 @@ module internal ViewModelHelper =
     let raiseErrorsChanged name =
       log.LogTrace("[{BindingNameChain}] ErrorsChanged {BindingName}", nameChain, name)
       helper.ErrorsChanged.Trigger([| helper.GetSender (); box <| DataErrorsChangedEventArgs name |])
-
-    let eventsToRaise =
-      helper.Bindings
-      |> Seq.collect (fun (Kvp (name, binding)) -> Update(helper.LoggingArgs, name).Recursive(helper.Model, newModel, binding))
-      |> Seq.toList
+    
     eventsToRaise
     |> List.iter (function
       | ErrorsChanged name -> raiseErrorsChanged name
       | PropertyChanged name -> raisePropertyChanged name
       | CanExecuteChanged cmd -> cmd |> raiseCanExecuteChanged)
 
-    { helper with Model = newModel }
-
 type [<AllowNullLiteral>] internal DynamicViewModel<'model, 'msg>
       ( args: ViewModelArgs<'model, 'msg>,
         bindings: Binding<'model, 'msg> list)
@@ -168,7 +167,9 @@ type [<AllowNullLiteral>] internal DynamicViewModel<'model, 'msg>
     member _.CurrentModel : 'model = helper.Model
 
     member _.UpdateModel (newModel: 'model) : unit =
-      helper <- ViewModelHelper.updateModel newModel helper
+      let eventsToRaise = ViewModelHelper.getEventsToRaise newModel helper
+      helper <- { helper with Model = newModel }
+      ViewModelHelper.raiseEvents eventsToRaise helper
 
   override _.TryGetMember (binder, result) =
     log.LogTrace("[{BindingNameChain}] TryGetMember {BindingName}", nameChain, binder.Name)