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<body lang="EN-US" link="#0563C1" style="overflow-wrap:break-word; word-break: break-word;word-wrap:break-word" vlink="#954F72"><div class="mail_android_message" style="line-height: 1; padding: 0.5em">I had a similar idea in the past and like the idea.<br/>Ideally, setting/switching a skin is a one step process. Currently you can construct a skin for a control and set it after to a different control.<br/><br/>Your approach sounds good, if you can set a skin by creating a new skin (with a default constructor) and then the setSkin() method will actually trigger the install process on the control (this), this will work and solve the problem above. But for backward compatibilty we still need to keep the skin constructor with the control as parameter and think about deprecating it.<br/><br/>-- Marius</div><div class="mail_android_quote" style="line-height: 1; padding: 0.3em"><html><body>Am 20.07.22, 23:40 schrieb Andy Goryachev <andy.goryachev@oracle.com>:</body></html><blockquote class="gmail_quote" style="margin: 0.8ex 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
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<p class="MsoNormal"><span style="font-family:"Courier New",serif">Hi,</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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!</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">Thank you,</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">-andy</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">Summary</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">-------</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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().</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">Problem</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">-------</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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. </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">This creates two problems:</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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.</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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.</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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">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:</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8245145 Spinner: throws IllegalArgumentException when replacing skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8245303 InputMap: memory leak due to incomplete cleanup on remove mapping</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8268877 TextInputControlSkin: incorrect inputMethod event handler after switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8236840 Memory leak when switching ButtonSkin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8240506 TextFieldSkin/Behavior: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8242621 TabPane: Memory leak when switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8244657 ChoiceBox/ToolBarSkin: misbehavior on switching skin </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8245282 Button/Combo Behavior: memory leak on dispose</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8246195 ListViewSkin/Behavior: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8246202 ChoiceBoxSkin: misbehavior on switching skin, part 2</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8246745 ListCell/Skin: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8247576 Labeled/SkinBase: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8253634 TreeCell/Skin: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8256821 TreeViewSkin/Behavior: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8269081 Tree/ListViewSkin: must remove flow on dispose</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8273071 SeparatorSkin: must remove child on dispose</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8274061 Tree-/TableRowSkin: misbehavior on switching skin</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">JDK-8244419 TextAreaSkin: throws UnsupportedOperation on dispose</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</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">Solution</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">--------</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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.</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">Specifically, I'd like to propose the following changes:</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> 1. Add Skin.install() with a default no-op implementation.</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</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()</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().</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">Impact Analysis</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">-------------</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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. </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </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.</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif">The change will require CSR as it modifies a public API.</span></p>
<p class="MsoNormal"><span style="font-family:"Courier New",serif"> </span></p>
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