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<p>Hi Andy,</p>
<p>Was a single step install process considered, something like:</p>
<p> control.installSkin(MySkin::new);</p>
<p>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.</p>
<p>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.<br>
</p>
<p>--John</p>
<div class="moz-cite-prefix">On 20/07/2022 23:39, Andy Goryachev
wrote:<br>
</div>
<blockquote type="cite"
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<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">I'd like to propose an API change in Skin
interface (details below). Your feedback will be greatly
appreciated!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Thank you,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">-andy<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Summary<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">-------<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">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().<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Problem<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">-------<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">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. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">This creates two problems:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"> 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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"> 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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">We can see the damage caused by looking at
<a href="https://bugs.openjdk.org/browse/JDK-8241364"
moz-do-not-send="true">JDK-8241364</a> </span><span
style="font-family:"Apple Color Emoji"">☂</span><span
style="font-family:"Courier New",serif">
<i>Cleanup skin implementations to allow switching</i>,
which refers a number of bugs:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8245145 Spinner: throws
IllegalArgumentException when replacing skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8245303 InputMap: memory leak due to
incomplete cleanup on remove mapping<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8268877 TextInputControlSkin: incorrect
inputMethod event handler after switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8236840 Memory leak when switching
ButtonSkin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8240506 TextFieldSkin/Behavior:
misbehavior on switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8242621 TabPane: Memory leak when
switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8244657 ChoiceBox/ToolBarSkin:
misbehavior on switching skin
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8245282 Button/Combo Behavior: memory
leak on dispose<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8246195 ListViewSkin/Behavior:
misbehavior on switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8246202 ChoiceBoxSkin: misbehavior on
switching skin, part 2<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8246745 ListCell/Skin: misbehavior on
switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8247576 Labeled/SkinBase: misbehavior
on switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8253634 TreeCell/Skin: misbehavior on
switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8256821 TreeViewSkin/Behavior:
misbehavior on switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8269081 Tree/ListViewSkin: must remove
flow on dispose<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8273071 SeparatorSkin: must remove
child on dispose<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8274061 Tree-/TableRowSkin: misbehavior
on switching skin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8244419 TextAreaSkin: throws
UnsupportedOperation on dispose<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">JDK-8244531 Tests: add support to identify
recurring issues with controls et al<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Solution<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">--------<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Specifically, I'd like to propose the
following changes:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"> 1. Add Skin.install() with a default no-op
implementation.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"> 2. Clarify skin
creation-attachment-detachment sequence in Skin and
Skin.install() javadoc<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"> 3. Modify Control.setSkin(Skin) method (==
invalidate listener in skin property) to call
oldSkin.dispose() followed by newSkin.install()<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"> 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().<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">Impact Analysis<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">-------------<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">The changes should be fairly trivial. Only
a subset of skins needs to be refactored, and the
refactoring itself is trivial. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif">The change will require CSR as it modifies
a public API.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier
New",serif"><o:p> </o:p></span></p>
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