I think you need to add a variable to your model that records whether the
editor is being used and then in yout subscription you have
myKbdSubs model =
if model.editorBeingUsed then
Sub.none
else <whatever you already have>
On Thursday, 19 October 2017 00:34:35 UTC+2, Dave Doty wrote:
I am using this Ace Editor adapted to Elm:
> https://github.com/DenisKolodin/elm-ace
>
> However, my problem seems not specific to that editor, but applies to any
> program that wants to support an embedded editor whose contents can be
> updated by the program, and also that can respond to global keypress events.
>
> The editor text can be updated either by
>
> 1) the user typing, or
> 2) the program updating the text (e.g., pressing a "load default text"
> button)
>
> The user can also press some keyboard shortcuts (',' and '.') to do other
> actions. These are handled by my update function:
>
> update msg model =
> ...
> KeyMsg keyCode ->
> if keyCode == Char.toCode ',' then
> update Backward model
> else if keyCode == Char.toCode '.' then
> update Forward model
> else
> ( model, Cmd.none )
>
> This is called whenever the user presses any key because of this
> subscription that uses the elm-lang/keyboard library:
>
> subscriptions model =
> Keyboard.presses KeyMsg
>
> The problem is that all of the keypresses made when editing cause the
> update function to be called, not just the two that I care about. Most of
> them are not ',' or '.' so the model is returned unchanged in the else
> clause above.
>
> But this causes the following problem: in my view function, the editor
> updates its contents to be whatever the model says the text should be (for
> instance, the user may press a button that loads some default text):
>
> view model =
> ...
> Ace.toHtml
> [ Ace.value model.text -- updates editor to display model.
> text
> , Ace.onSourceChange NewText -- updates model.text to be latest
> editor contents
> ]
> []
>
> The purpose of onSourceChange above is to trigger another call to the
> update function, which allows me to update my model text with the new
> editor contents. In other words, the two lines above are the bi-directional
> data binding between model.text and the editor's text contents. The
> second one implies a call to the update function:
>
> update msg model =
> ...
> NewText newText ->
> ( {model | text = newText}, Cmd.none )
>
> The problem is that the Elm runtime is ordering events so that the text in
> the editor never gets updated when the user tries to type new text.
>
> Here is the order of events:
>
> 1. User types to edit text in the editor.
> 2. Because of the subscription I registered for global keystroke
> events, Elm runtime calls update with the message KeyMsg indicating
> which key was pressed.
> 3. Model is updated (in the KeyMsg case of my update function) to the
> "new" model, but most of the time this is identical to the old model since
> only ',' and '.' actually return a changed model. Importantly, this is
> the *old* text, not containing the new character that the user typed.
> 4. The view function is called, and the Ace.toHtml updates the text
> contents of the editor to be what the model.text field is... which erases
> in the editor the new character that the user just tried to enter, since
> model.text still has the old, pre-keystroke text.
> 5. The update function is called with a NewText message, but it's too
> late. By now the editor has had its new text erased and replaced with the
> old text. Ideally, this event would have happened in between steps 1 and
> 2,
> but steps 2,3,4 seem to happen before this does.
>
> I'm not sure how to get around this.
>
> *Idea 1:* figure out a way to prevent the update function from being
> called at all when a keystroke other than ',' or '.' occurs. This is not
> ideal because then they can't type ',' or '.' in the editor, but it would
> be a workaround because I could perhaps assign Ctrl+... keys or something.
>
> *Idea 2:* Re-order the updates so that, when the user enters new text in
> the editor, it is guaranteed that update is called with the NewText message
> before it is called with the KeyMsg message. I don't know of any way to do
> this.
>
> *Idea 3:* Re-design how I'm passing messages through the system so that,
> no matter the order in which messages are delivered, if the user tries to
> enter new text, eventually that new text makes its way into the model.
>
> *Idea 4:* don't use the Keyboard library to respond to global keypress
> events, and find something that is more specific to what I want (to give
> the user a couple of keyboard shortcuts, without calling the update
> function every time any key is pressed). Suggestions for such a library?
>
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