RFR: 8375588: Enhanced property metadata

[Andy Goryachev]

On Tue, 20 Jan 2026 21:32:23 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>>> JavaFX already has this concept today, but we're not using the `Property` API to model it. Layout constraints like `GridPane.columnIndex` or `HBox.margin` are implemented as static getter/setter pairs. Since they are not first-class properties, you don't get any of the nice property features (bindings, listeners, styling, etc).
>> 
>> I always found this design to be weird and unnecessary - these should be the properties/constraints of the container or the layout, not something stored in the child nodes.  What happens when the said child is moved from one container to another??
>> 
>> It might be just me, but I fail to see the value of this proposal.
>
>> > JavaFX already has this concept today, but we're not using the `Property` API to model it. Layout constraints like `GridPane.columnIndex` or `HBox.margin` are implemented as static getter/setter pairs. Since they are not first-class properties, you don't get any of the nice property features (bindings, listeners, styling, etc).
>> 
>> I always found this design to be weird and unnecessary - these should be the properties/constraints of the container or the layout, not something stored in the child nodes. What happens when the said child is moved from one container to another??
>> 
>> It might be just me, but I fail to see the value of this proposal.
> 
> This is basically the JavaFX way to attach layout information to nodes, used by `GridPane`, `HBox`, `StackPane`, etc.  In Swing this is handled differently by making layout constraints a 2nd parameter when adding a node (like `GridBagConstraints`), in FX this is done via the general `Properties` map which is much more flexible.  Extending this system so they become full, observable properties, and even styleable properties is a very logical step.  Making them styleable for example will allow you to move them to CSS:
> 
> 
> .button {
>     -fx-hbox-margin: 10 10 10 10;
>     -fx-hbox-hgrow: ALWAYS;
> }
> 
> This is currently one of the biggest missing features when it comes to styling controls, having to go to programmatic configuration for these kinds of styling properties.

Thank you @hjohn this example makes sense.

So, if I understand it correctly, the proposal is to add two-tiered styleable properties?  Are there limitations as to which attached property is legal for which node, or any attached property (including custom) can be attached to any node?  I understand that CSS part is not there yet, but perhaps this PR should instead go via `HasAttachedProperties` route?

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PR Comment: https://git.openjdk.org/jfx/pull/2015#issuecomment-3775125620