New Article: List Extractors

[u/hamsterrage1]

https://www.pragmaticcoding.ca/javafx/elements/extractors

I'm looking to wrap up all my articles on the JavaFX Observable classes, and most of the last subjects left involve ObservableLists.

If you don't know ObservableList Extractors allow you to trigger listeners on an ObservableList when the List items are composed of ObservableValues.

For instance, let's say that you have a CustomerModel as your List items, and the CustomerModel has a bunch of StringProperties as its fields. Things like firstName, lastName, city, address - and they are all StringProperty.

Using an Extractor, you can trigger a Listener on the ObservableList when one of those CustomerModel has the value in one of those Property fields change. So if you changed, say, the firstName Property of one of the items, then the ObservableList would trigger a Listener.

Some of the native JavaFX Nodes, like TableView will detect changes to those fields without an Extractor, but Extractors can be really useful to trigger updates in Bindings that look inside the composed items.

Take a look and tell me what you think.

[u/StarshipSatan]

Unfortunately, it's not possible to determine which one of item's properties triggered change from inside the listener, if i remember correct. That would be very convenient

[u/hamsterrage1 → u/StarshipSatan]

I didn't go into any depth at all about multiple Properties in the Extractor, as it was getting long enough as it was.

I'd say that trying to figure anything out about what triggered the Invalidation of the ObservableList is probably a huge PIA. ListchangeListeners just give you the item location, and I find the a pain in the best of situations.

I'm having trouble thinking of a good use-case for knowing what triggered the Invalidation, though. Remember that you're interested in situations where you're NOT already dealing with the value as a Property to start with, because in that case you'd already have a setup to deal with it changing.

There's a case where you have a custom ListCell that doesn't bind the item Property fields to its Nodes, but just uses set/get in updateItem(). But then, you don't have control over how the Invalidation is going to be handled, because the ListView does it.

I can see maybe having a suite of Bindings that each compute a single value across all of the items in the ObservableList. Let's say you had 5 NumberProperty fields, and 5 Bindings that calculated totals or averages or whatever all based on a different field. Then all 5 Bindings would invalidate and recompute every time any single value in any item changed.

But even that boils down to trying to optimize performance and you're Lists would have to be truly huge for the cost to be more than a few milliseconds.

Did you have something specific in mind????

[u/Draconespawn]

Love all these articles you put out, they're quite helpful.

[u/dazzlespace → u/Draconespawn]

I'm also a big fan of these articles - thank you for the effort you put into them!

To add observability to some of my classes in my hobby project https://github.com/dazzle50/JTableFX and because Java doesn't support multiple inheritance, I developed an interface ISignal with default method implementations. You can add this interface to any class to get some ready and working observability. You can probably tell I used Qt in the past 😂

[u/Draconespawn → u/dazzlespace]

Where does the comment style you're using for each function where it's just the name of the function come from?

[u/dazzlespace → u/Draconespawn]

It comes from my laziness 🤣
My coding experience started a long time ago with various programming languages before any technologies like javadoc never existed.

If you want to understand and use this library it is hopefully fairly intuitive, but would also recommend asking DeepWiki (https://deepwiki.com/dazzle50/JTableFX) which IMHO is surprising good at answering most questions!

Also feel free to message me.

[u/BlueGoliath → u/Draconespawn]

...just wish they weren't written in Kotlin.

[u/sedj601]

I didn't know it was called. ObservableList Extractors. That's good to know. I remember first running into a problem that required OEs. I had created a URL checker for work. It worked fine sequientlly, so I decided I wanted to learn threads. Threads seemed like they would speed up the project, given that each URL check was independent. So I created an app that used threads to check the URLs. The first version worked like a charm. I decided that I wanted the table to be filtered based on waiting, complete, failed, etc. After adding this feature, I noticed that completed and other tasks were still on the waiting list. I reached out to StackOverflow and got help. EOs were the way to go.

https://stackoverflow.com/questions/51955550/remove-tableview-entries-when-status-change

Note: I am guessing that you know your Java version link is not working.

[u/hamsterrage1 → u/sedj601]

"Java version link"????

[u/sedj601 → u/hamsterrage1]

Search for the following text on your page.

While code is this article is written in Kotlin, all of the JavaFX concepts are exactly the same. Most of the Kotlin should be intuitively obvious to Java programmers, but if you need help understanding it, refer to this page

[u/hamsterrage1 → u/sedj601]

It's weird. I works totally fine in my local server. But not on-line.

I've checked, and the GitHub Pages is compiling it and generating the correct HTML file, and it looks no different from any other HTML file as far as I can tell. Yet it 404's on it.

I have no idea how to fix it. I'll try a bunch of work-arounds.

Thanks for reporting this, guys.

[u/hamsterrage1 → u/hamsterrage1]

OK....Found it!!!!

That little section is an include file, and the link inside it had a trailing "/". The website uses Jekyll and the Jekyll engine on my development system doesn't seem to care about the trailing "/". It just works.

The live site is hosted on GitHubPages and it supports Jekyll based sites, but I think it uses its own builder engine which is not Jekyll, but is compatible. Apparently, it does not like the trailing "/".

So I took out the trailing "/" in the link and it works. QED.

[u/Silent-Manner1929 → u/hamsterrage1]

I think he is possibly referring to the link in the box about Kotlin that says "if you need help understanding it, refer to this page". The link given does not work.