Re: Aw: Re: Proposal: Add Skin.install() method

[Andy Goryachev]

I also prefer the minimal change, to lessen the impact on the existing code.

What worries me is that proposed check and an IllegalArgumentException if (getSkinnable() != Skinnable.this) cannot work in the case of PopupControl.

We could either say Skinnable.setSkin() may throw IllegalArgumentException under certain conditions, or remove the check completely.

https://github.com/openjdk/jfx/pull/845/files#r929291047

What do you think?

-andy

From: openjfx-dev <openjfx-dev-retn at openjdk.org> on behalf of Kevin Rushforth <kevin.rushforth at oracle.com>
Date: Tuesday, 2022/07/26 at 07:55
To: openjfx-dev at openjdk.org <openjfx-dev at openjdk.org>
Subject: Re: Aw: Re: Proposal: Add Skin.install() method
These additional change are more disruptive, and I don't see enough value to go down this path. I prefer to keep the existing constructor, and add the newly-proposed Skin::install method. Unless we find something very compelling that can't be done using that pattern, the cost of making a more intrusive change doesn't seem justified.

-- Kevin

On 7/26/2022 7:39 AM, Marius Hanl wrote:
I don't see how this fixes the underlying problem, since you could still do stuff like:

control.installSkin<http://control.installSkin>(c -> {
MySkin s = new MySkin(myOtherControl);
// configure stuff
return s;
});

So I think the super clean way would still be to have a default constructor for every skin, while keeping the control constructor for backwards compatibilty.

But a check is also already a good step.
It might be also worth to add a 'uninstall' method and move the 'dispose' method content into it and deprecate it.
Then it is much more clear from the wording, but is not 100% necessary.

-- Marius
Am 23.07.22, 14:49 schrieb John Hendrikx <john.hendrikx at gmail.com><mailto:john.hendrikx at gmail.com>:

Configuration can be part of the factory or not?

Simple case:

      control.installSkin(MySkin::new)

More complicated case:

      control.installSkin(c -> {
           MySkin s = new MySkin(c);
           // configure stuff
           return s;
      });

--John
On 22/07/2022 17:58, Andy Goryachev wrote:
> control.installSkin(MySkin::new);

This is an interesting idea.  Control.installSkin(Function<Control,Skin>).

One of the requirements we ought to consider is maximizing the backward compatibility.  If we were to add a new installSkin method it would not solve the problem with the old method, and replacing setSkin(Skin) with installSkin() would break compatibility with the existing code.

There is one more reason to allow for creation of a skin outside of setSkin() - configuration.  Imagine customer skins require configuration, in which case the sequence of events looks like this

instantiation -> configuration -> uninstall old skin -> install new skin.

with installSkin(MySkin::new) such a model will be impossible.

Thank you
-andy


From: openjfx-dev <openjfx-dev-retn at openjdk.org><mailto:openjfx-dev-retn at openjdk.org> on behalf of John Hendrikx <john.hendrikx at gmail.com><mailto:john.hendrikx at gmail.com>
Date: Thursday, 2022/07/21 at 15:49
To: openjfx-dev at openjdk.org<mailto:openjfx-dev at openjdk.org> <openjfx-dev at openjdk.org><mailto:openjfx-dev at openjdk.org>
Subject: Re: Proposal: Add Skin.install() method

Hi Andy,

Was a single step install process considered, something like:

     control.installSkin(MySkin::new);

This would also make it much more clear that Skins are single use only, where the API currently has to bend over backwards to make that clear and enforce it.

Other than that, I think your suggestion would be a definite improvement over the current situation. Something never felt quite right about how skins where set up and attached to controls, it felt fragile and cumbersome -- possibly as the result of relying on a writable property as the means to install a skin.

--John
On 20/07/2022 23:39, Andy Goryachev wrote:
Hi,

I'd like to propose an API change in Skin interface (details below).  Your feedback will be greatly appreciated!

Thank you,
-andy





Summary
-------

Introduce a new Skin.install() method with an empty default implementation.  Modify Control.setSkin(Skin) implementation to invoke install() on the new skin after the old skin has been removed with dispose().


Problem
-------

Presently, switching skins is a two-step process: first, a new skin is constructed against the target Control instance, and is attached (i.s. listeners added, child nodes added) to that instance in the constructor.  Then, Control.setSkin() is invoked with a new skin - and inside, the old skin is detached via its dispose() method.

This creates two problems:

 1. if the new skin instance is discarded before setSkin(), it remains attached, leaving the control in a weird state with two skins attached, causing memory leaks and performance degradation.

 2. if, in addition to adding listeners and child nodes, the skin sets a property, such as an event listener, or a handler, it overwrites the current value irreversibly.  As a result, either the old skin would not be able to cleanly remove itself, or the new skin would not be able to set the new values, as it does not know whether it should overwrite or keep a handler installed earlier (possibly by design).  Unsurprisingly, this also might cause memory leaks.

We can see the damage caused by looking at JDK-8241364<https://bugs.openjdk.org/browse/JDK-8241364> ☂ Cleanup skin implementations to allow switching, which refers a number of bugs:

JDK-8245145 Spinner: throws IllegalArgumentException when replacing skin
JDK-8245303 InputMap: memory leak due to incomplete cleanup on remove mapping
JDK-8268877 TextInputControlSkin: incorrect inputMethod event handler after switching skin
JDK-8236840 Memory leak when switching ButtonSkin
JDK-8240506 TextFieldSkin/Behavior: misbehavior on switching skin
JDK-8242621 TabPane: Memory leak when switching skin
JDK-8244657 ChoiceBox/ToolBarSkin: misbehavior on switching skin
JDK-8245282 Button/Combo Behavior: memory leak on dispose
JDK-8246195 ListViewSkin/Behavior: misbehavior on switching skin
JDK-8246202 ChoiceBoxSkin: misbehavior on switching skin, part 2
JDK-8246745 ListCell/Skin: misbehavior on switching skin
JDK-8247576 Labeled/SkinBase: misbehavior on switching skin
JDK-8253634 TreeCell/Skin: misbehavior on switching skin
JDK-8256821 TreeViewSkin/Behavior: misbehavior on switching skin
JDK-8269081 Tree/ListViewSkin: must remove flow on dispose
JDK-8273071 SeparatorSkin: must remove child on dispose
JDK-8274061 Tree-/TableRowSkin: misbehavior on switching skin
JDK-8244419 TextAreaSkin: throws UnsupportedOperation on dispose
JDK-8244531 Tests: add support to identify recurring issues with controls et al


Solution
--------

This problem does not exist in e.g. Swing because the steps of instantiation, uninstalling the old ComponentUI ("skin"), and installing a new skin are cleanly separated.  ComponentUI constructor does not alter the component itself, ComponentUI.uninstallUI(JComponent) cleanly removes the old skin, ComponentUI.installUI(JComponent) installs the new skin.  We should follow the same model in javafx.

Specifically, I'd like to propose the following changes:

 1. Add Skin.install() with a default no-op implementation.
 2. Clarify skin creation-attachment-detachment sequence in Skin and Skin.install() javadoc
 3. Modify Control.setSkin(Skin) method (== invalidate listener in skin property) to call oldSkin.dispose() followed by newSkin.install()
 4. Many existing skins that do not set properties in the corresponding control may remain unchanged.  The skins that do, such as TextInputControlSkin (JDK-8268877), must be refactored to utilize the new install() method.  I think the refactoring would simply move all the code that accesses its control instance away from the constructor to install().


Impact Analysis
-------------

The changes should be fairly trivial.  Only a subset of skins needs to be refactored, and the refactoring itself is trivial.

The new API is backwards compatible with the existing code, the customer-developed skins can remain unchanged (thanks to default implementation).  In case where customers could benefit from the new API, the change is trivial.

The change will require CSR as it modifies a public API.


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