I also like this route, perhaps slightly more, depending on how far this
can be taken:
Disclaimer: I dislike the CSSMetaData and special property subclass a
lot -- it's a major concession to make properties work with the CSS
system that brings a lot of boilerplate that is mostly unnecessary.
If you go the route of an annotation, we could offer to do everything
via the annotation so a regular property can be converted to styleable
by annotating it. The property would then have to specify the name
("-fx-label-padding") and the default value (which can be a string that
is parseable via the existing CSS parser).
In other words:
@Styleable(name = "-fx-label-padding", defaultValue = "(0, 0, 0, 0)")
publicfinalReadOnlyObjectProperty<Insets> labelPaddingProperty() { ... }
The rest the scanner can figure out (it could even figure out a default
name). The `isSettable` method is always the same boilerplate (and if
not, you can use the old way). The required converter can be derived
from the generic type (Insets -> InsetsConverter), or specified
(converter = InsetsConverter.class).
To convert a regular property into a styleable does require somewhat
more magic (the CSS system would have to wrap it, or otherwise track
them) but that's all hidden. It gets rid of the StyleableProperty
uglyness and the need for users to create those, and puts the "extra"
CSSMetaData information a styleable property needs firmly where it
belongs (in an annotation).
--John
On 06/12/2023 11:37, Nir Lisker wrote:
I thought about the option of reflection, but I opted to propose
annotations instead. The following is my reasoning.
Firstly, reflection is very magic-y. The author of the class has no
indication of what side effects happen due to the code they write, the
output (css handling in this case) comes out of nowhere from their
perspective. As with other reflection cases, it is a "pull" rather
than "push" approach - you don't write what should happen, you let
someone else decide that. For writers of skin/control classes, this
means that they need to know exactly what constitutes a hook for the
reflection mechanism, or face surprises. There is no compile time
check that tells you whether you have declared your styleable property
properly or not (without an external ad-hoc checker).
We do this somewhat with properties - any method of the form
"...property()" gets special treatment, but this is for the docs. I
don't think we have code that depends on this other than in tests.
Secondly, the proposed mechanism depends on the runtime type, not the
declared type. As a user, I see no indication in the API whether a
property is styleable or not. This is also (what I would consider) a
problem with the current state. When I thought about using reflection
to solve this, I at least thought to specify the declared type of the
property as styleable, like StyleableBooleanProperty instead of
BooleanProperty (restricting the returned type is backwards
compatible). A downside of this is that it gives access to the methods
of StyleableProperty, which are not useful for the user, I think, but
maybe someone has a use for them.
Thirdly, maybe I want to declare a styleable property not to be used
automatically. I can't think off the top of my head when I would want
to do that, but I'm also not a heavy css user. Are we sure that just
initializing a property with a styleable runtime type should *always*
be caught by this process?
To compare, annotations have the following benefits:
Firstly, they are declarative, which means no surprises for the class
author (WYSIWYG). This also allows more flexibility/control over which
properties get special treatment via an opt-in mechanism.
Secondly, They can also be displayed in the JavaDocs (via @Documented)
with their assigned values. For example, the padding property of
Region can be annotated with @Styleable(property="-fx-padding"),
informing the user both that this value can be set by css, and how to
do it. Interestingly, the annotation doesn't need to be public API to
be displayed, so we are not bound by contracts.
In terms of similarities:
In both the reflection and the annotation proposals, the steps are:
1. Create styleable properties.
2. That's it.
It's just that step 1 also adds an annotation to the creation of the
property (which was/is a 2-step process anyway, declaring the property
and its css metadata).
Annotations also require a processor to read the data from their
values and target (the field/method). This is a bit of work, but
Michael's CssMetaDataCache class is basically that - read the data
from the class (via reflection or annotations) and store it in a map.
The logic should be the same, just the method to obtain the data is
different. Both, as a result, have the benefits of handling
control/skin combinations (what I mentioned in the point "Usable both
in controls and in skins (or other classes)").
The benefit of co-locating the property and its css metadata in the
class itself also remains.
To summarize, both approaches eliminate all the clutter of writing
styleable properties (John, will you like to create styleable
properties now? [1] :) ), both apply the flexibility of caching per
class, both allow better structuring of the class, but they read the
properties differently and have a different level of declarativness.
[1]
https://mail.openjdk.org/pipermail/openjfx-dev/2023-December/044010.html
On Tue, Dec 5, 2023 at 11:21 PM Andy Goryachev
<andy.goryac...@oracle.com> wrote:
I like the idea.
I wonder if it is possible to reduce the amount of boilerplate
code? For example, a CssMetaData can have a
setGetter(Function<S, StyleableProperty<V>> getter)
method which supplies the property reference? This way
CssMetaData.isSettable(Node) and
CssMetaData.getStyleableProperty(Node) can be implemented in the
base class (there are more complicated cases, so perhaps
setIsSettable(Predicate<Node>) would also be required).
Example:
CssMetaData.<ControlExample,Font>of("-fx-font", Font.getDefault(),
(n) -> n.font)
Just a thought. What do you think?
-andy
*From: *openjfx-dev <openjfx-dev-r...@openjdk.org> on behalf of
Michael Strauß <michaelstr...@gmail.com>
*Date: *Sunday, December 3, 2023 at 22:02
*To: *openjfx-dev <openjfx-dev@openjdk.org>
*Subject: *Reflective discovery of styleable properties
Following up the discussion around the CssMetaData API, I'd like to
chime in with yet another idea. To recap, here's Nir's summary of the
current API [0]:
"Let's look at what implementation is required from a user who wants
to write their own styleable control:
1. Create styleable properties.
2. Create a list of these properties to be passed on.
3. Create a public static method that returns the concatenation of
this list with the one of its parent. (This method happens to be
poorly documented, as mstr said.)
4. Create a public non-static method that calls the static method in a
forced-override pattern because otherwise you will be calling the
wrong static method. (This method's docs seem to be just wrong because
you don't always want to delegate to Node's list.)"
I think this could reasonably be replaced with the following
implementation requirements:
1. Create styleable properties.
2. That's it.
Let's look at what we're actually trying to do: create a list of
CSS-styleable property metadata of a class. But we can easily do that
without all of the boilerplate code.
When ´Node.getCssMetaData()` is invoked, all public methods of the
class are reflectively enumerated, and metadata is retrieved from
`Property` and `StyleableProperty` getters. This is a price that's
only paid once for any particular class (i.e. not for every instance).
The resulting metadata list is cached and reused for all instances of
that particular class.
As a further optimization, metadata lists are also cached and
deduplicated for Control/Skin combinations (currently every Control
instance has its own copy of the metadata list).
Another benefit of this approach is that the CssMetaData can now be
co-located with the property implementation, and not be kept around in
other parts of the source code file. Here's how that looks like when a
new "myValue" property is added to MyClass:
StyleableDoubleProperty myValue =
new SimpleStyleableDoubleProperty(this, "myValue") {
static final CssMetaData<MyClass, Number> METADATA =
new CssMetaData<MyClass, Number>(
"-fx-my-value",
SizeConverter.getInstance(),
USE_COMPUTED_SIZE) {
@Override
public boolean isSettable(MyClass node) {
return !node.myValue.isBound();
}
@Override
public StyleableProperty getStyleableProperty(
MyClass node) {
return node.myValue;
}
};
@Override
public CssMetaData getCssMetaData() {
return METADATA;
}
};
public final DoubleProperty myValueProperty() {
return myValue;
}
It is not required to override the `getCssMetaData()` method, nor is
it required to redeclare a new static `getClassCssMetaData()` method.
It is also not required to manually keep the list of styleable
properties in sync with the list of CSS metadata.
I've prototyped this concept for the `Node`, `Region` and
`Control` classes [1].
[0]
https://mail.openjdk.org/pipermail/openjfx-dev/2023-December/044046.html
[1] https://github.com/openjdk/jfx/pull/1299
