Clearing a SourceList?

[houstonhaynes]

@JordanMarr this is an odd question - as it's really a two-parter. So I sending a message from my MainViewModel to my ChatViewModel. I have a button (that resides in MainVM) which dispatches a command to clear the SourceList that populates the chat items in the chat window.

Here's the ClearChatCommand in the ChatView.axaml

And the binding in the ViewModel

member this.ClearChatCommand() =
        local.Dispatch ClearChatCommand

and the branch in the update function

| ClearChatCommand ->
            ChatViewModel.DesignVM.ClearChat()
            model

So far, so good, right? I know! I'm as surprised as anyone. 😸

In the ChatViewModel here's ClearChat()

member this.ClearChat() =
        local.Dispatch(ClearChat)

Which then executes in the update function in the "ClearChat" branch\

| ClearChat ->
            printfn "clearing chat history"
            model.Messages.Clear()
            model

and I've also tried

| ClearChat ->
            printfn "clearing chat history"
            { model with Messages = model.Messages |> SourceList.removeAll }

and then - similar to the init()

| ClearChat ->
            printfn "clearing chat history"
            { model with Messages = SourceList.createFrom [] }

and finally in desparation I'm running the init() - which in context here is pretty tame

| ClearChat ->
            printfn "clearing chat history"
            init() |> ignore
            model

Even better - when I click the button - I see the console echo "clearing chat history" faithfully every time the action is taken. And yet, nothing happens in the chat window. All of the chat messages are still present. :/

Was it something I said, something I didn't say? Is there something about SourceList that I need to know.

1. Am I routing the command from the MainView to the ChatView in a way that's consistent with your concept of passing messages from MVU loop to MVU loop? I tried to use a mechanism similar to what you used for "GoHome" but thought the "direct route" from Main to Chat view made sense here. Should I route through App?
2. Is there something I'm missing about either how SourceList works, or how returning the model with an initialized "Messages" should be asserted?

Any help/pointers/advice would be appreciated!

[JordanMarr]

Could it be related to using the Items property?

[JordanMarr]

What was the issue?

[houstonhaynes]

This?

| ClearChat ->
            printfn "clearing chat history"
            { model with Messages = model.Messages |> SourceList.removeAll }

Doesn't work - also

| ClearChat ->
            printfn "clearing chat history"
            model.Messages.RemoveRange(0, model.Messages.Count - 1 )
            model

Doesn't work

[JordanMarr]

But it does work the sample.

[houstonhaynes]

I don't know what to say - it's a conundrum

[houstonhaynes]

I just tried this method - same non result...

| ClearChat ->
      printfn "clearing chat history"
      let resetMessages = seq<ChatMessage>[]
      { model with Messages = model.Messages |> SourceList.removeAll |> SourceList.addRange resetMessages }

And for the record I'm on ReactiveElmish.Avalonia 1.0.2

[JordanMarr]

Hard to tell what the issue is. Your individual snippets all look fine.

[JordanMarr]

I just realized that you are calling the DesignVM property to clear the chat.

        | ClearChatCommand ->
            ChatViewModel.DesignVM.ClearChat() // <- This is the problem
            model

[houstonhaynes]

I've tried so many ways to get this done I've lost my mooring.

[JordanMarr]

There are a bunch of ways you could call the ClearChat() method from the MainViewModel.
The easiest way would probably be to just do this:

    member this.ClearChatCommand() =
        let chatView = this.ChatView :> StyledElement
        let chatVM = chatView.DataContext :?> ChatViewModel
        chatVM.ClearChat()

There is no real value to be gained by pushing that into the local Elmish loop, so better to just delete the ClearChatCommand message in your MainViewModule and call the ChatViewModel directly from your MainViewModel.

Another way to do it would be to move your chat messages into the App module as global app state. But it's not worth breaking up the modularity you have just to facilitate sharing the ClearChat method.

Yet another way would be to use the EventBus pattern that I had in one of the earlier versions of the sample app.

[houstonhaynes]

Outstanding - thanks. We talked about moving chat into the app module but have held off. Your notes are really great food for thought. 👍