What can I do in case when no observer to fire? (Pages/Scenes)

dezmo · December 5, 2021, 1:34pm

Situation:
I want to detect (among others) when a user changes of the properties of a page (Scene) and update my HtmlDialog if it is visible.

The problem is that I can’t really find an Observer that can be used.

@DanRathbun has already summarized the good part of my situation very well here, so I won’t repeat it:

github.com/SketchUp/api-issue-tracker

PagesObserver#onPageUpdate() observer callback

opened 03:10PM - 17 Jan 18 UTC

DanRathbun

enhancement Ruby API SketchUp logged

### SketchUp Ruby API Feature Request The API is missing an `onPageUpdate()` …observer callback. Tests show nothing firing when a page is updated. I attached a test observer to the page, the pages collection and the entities collection. Got no response. **1. Use-case:** One case is what is described in Eneroth3's FR: https://github.com/SketchUp/api-issue-tracker/issues/25 When a page update callback fired, she could check her extension's data to sync it with what the page is doing with the view's properties, ... **camera**, **section planes**, etc. **2. Suggested pattern / parameters:** **One** pattern of arguments passed into the callback **could** be: **`pages, page, old_flags, new_flags`**. It would make dealing with changes much better if the flags prior to the update could be compared with the new flags. **ADD**: This would be a bulk callback pattern where 1 call would be made after a scene page update. If this pattern is chosen, the flags would be st be passed as hash arguments as described [below in post 5](https://github.com/SketchUp/api-issue-tracker/issues/26#issuecomment-691034098) ... ```ruby def onPageUpdate(pages, page, old_flags, new_flags) if old_flags != new_flags # The page property set changed ! changed = (old_flags - new_flags).abs end end ``` **OR**, ... ... another pattern of arguments passed into the callback **could** be: **`pages, page, property, old_value, new_value`**. This would be an individual callback pattern where a call would be made **for each changed property**, **either** after a scene page update ... or **immediately after** the actual change of an individual property or update flag. In this scenario the callback name does not need to reflect "update" as there are several properties that can change independent of an update, which have no current observer firing (or that helps identify the page and property that changed. Ie [`PagesObserver#onContentsModified`](https://ruby.sketchup.com/Sketchup/PagesObserver.html#onContentsModified-instance_method) fires for some changes but does not pass the reference of the page whose property changed, nor the property that changed, making the firing almost worthless to coders. _[See list below for details](https://github.com/SketchUp/api-issue-tracker/issues/26#issuecomment-691744240)_.) So given this (and the fact that [`EntityObserver#onChangeEntity`](https://ruby.sketchup.com/Sketchup/EntityObserver.html#onChangeEntity-instance_method) does **not** fire at all for scene page entity objects (when it should have,) it might be better to name the callback `"onPageChanged"` ... ... and have it fire for changes to: `:name`, `:description`, `:delay_time`, `:include_in_animation`, `:transition_time`, _etc._, **in addition to** the update flags (and _possibly_ the page's **position** in the collection as [`PagesObserver#onContentsModified`](https://ruby.sketchup.com/Sketchup/PagesObserver.html#onContentsModified-instance_method) fires **once** when a page's position is changed but doesn't give any info to determine which page was moved, and what other pages had their positions adjusted accordingly.) ```ruby def onPageChanged(pages, page, property, old_value, new_value) if property == :use_axes && new_value # The axes is being saved, so ... MyPlugins::AxesHistory.save_axes(page.name, page.axes.transformation) end end ``` **2. Suggested implementation / reasoning:** I think it best that this callback be added to the **[`Sketchup::PagesObserver`](http://ruby.sketchup.com/Sketchup/PagesObserver.html)** class documentation, as that is where coders will be looking for it. (Yes observers are abstract now, but this is about where coders "attach" observers, see below) This is also where they are likely to wish to attach such an observer. (It is tedious to be forced to attach an observer to each item in a collection, so I'd vote **against** putting this in the [**`Sketchup::EntityObserver`**](http://ruby.sketchup.com/Sketchup/EntityObserver.html) class, which would force coders to attach to each and every page instance. **Ie, SketchUp should poll the observers attached to the collection for a callback method, instead of the _possibly many_ observers attached to the page entity itself.** (Easier and faster for everyone!) ~

As a matter of fact, changes to the above mentioned properties are not currently detectable through the Ruby API.

I have some ideas for workarounds, but none of them seems an ideal:

Open HtmlDialog as a modal dialog.
So the user has no chance to change…problem solved …Easy
Of course, this would all lose the purpose of my dialog to interact or see the information as long as the user is using other tools or operation. So, I do not really like it.
I will instruct the user (RTFM :-)) to update the data (press a button) if they feel that the changes made may affect the data in the dialog.
This is not elegant at all.
After I open the HtmlDialog, I start a timer (1-5 sec) that periodically collects and sends the changes to the dialog. Then, when the dialog closes, of course I also stop the timer and sending data’s.
I don’t know how stressful is this for Ruby engine, but sure the dialog will flicker less or more… periodically. (And can be conflicting with the operation what the user is doing inside the HtmlDialog exactly the same time when the updated data arriving …)
After I open the HtmlDialog, I will detect (JavaScript) if the mouse cursor enter or leave the dialog, then send a callback to SU accordingly to update the data.
The point is, that I can not be perfectly define what the “accordingly” can be in details…

So, what other ideas or comments are there?
Please share your thoughts!

DanRathbun · December 5, 2021, 5:11pm

(4) is preferable to using a timer as in (3). Besides if the mouse cursor is inside the dialog, they cannot be making manual changes to the Scenes inspector.

You can also use a mouse over event of the description element to check and update that 1 data item as it 's changes do not fire any observers at all.

Otherwise you will need to cache all values for each page and do comparisons for #onContentsModified as explained in my last post:

PagesObserver#onPageUpdate() observer callback · Issue #26 · SketchUp/api-issue-tracker · GitHub

… and …

Add observer event to detect active scene change · Issue #237 · SketchUp/api-issue-tracker · GitHub

You might have a toggle switch to control (3)'s timer when it interferes with other modeling operations.

But you should only update what changes and only update the values of HTML elements, not redraw the entire page which will cause flickering.

dezmo · December 5, 2021, 6:33pm

Thanks, Dan!

Sounds very reasonable to combine (3) & (4). In my tests, flickering only noticeable when the focus on the dialog and pushing data periodically. If the user working on the model or on SU native UI, update some Html elements (even entirely Html page) every 2 seconds flickering is not visible.

I will check you other suggestion too.

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What can I do in case when no observer to fire? (Pages/Scenes)

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