In addition to the points John raises, I also agree with the comment Tom
added to the Draft PR: I don't think the object bindings in javafx.base
should have UI concepts like Action or Focus, even if you abstract them
a bit.
-- Kevin
On 11/10/2021 3:10 AM, John Hendrikx wrote:
Although I think you have a valid use case, I don't think JavaFX
should facilitate this exact scenario; it is a high level concern that
you want to solve in a very low level mechanism. A similar scenario
also applies to uni-directional bindings, so I think it would have to
apply there as well.
It also really depends on how you are doing the communication between
view and model. Some system use models that are always valid, some
systems use a view-model that contains a direct copy of what is in the
UI controls. Some views allow users to type anything and do validation
on submission or focus loss; some do per character validation and mark
bad input; some will not even allow you to type bad input.
For a scenario like you describe, which seems to be about delayed
updates of bindings, I think you really want to use something like
ReactFX's EventStreams. These offer far more features, including
timeouts, removal of duplicates, combining of values, conditional
suspending, etc. It might work like this for example:
EventStream.of(textInput.textProperty())
.conditionOn(textInput.focusedProperty().not())
.feedTo(model::valueProperty);
Or with Val:
Val.of(textInput.textProperty())
.conditionOn(textInput.focusedProperty().not())
.subcribe(v -> updateModel(v));
(Note: conditionOn is part of the fluent bindings proposal that Nir
Lisker and me have been working on).
Now, this isn't bidirectional, but I don't see how that will work in
any case as there are some edge cases. For example, how would you
handle a model update when the view is currently being edited?
Delaying updates runs into issues where both may have changed, whereas
currently bindings are resolved immediately on the FX thread.
--John
On 10/11/2021 06:45, Michael Strauß wrote:
JavaFX developers routinely use programming patterns like MVC, MVP, or
MVVM to separate views from their associated business logic. Bindings
can be used to connect the values of UI controls (like Label or
TextField) to properties on a business logic class.
A typical (simplified) scenario may look like this:
var valueField = new TextField();
valueField.textProperty().bindBidirectional(businessLogic.valueProperty());
The business logic class may perform data validation or other actions
on the value that was entered in the TextField. However, in many
cases, it is neither necessary nor desirable for the binding to update
the business-layer property on every single change (i.e. every single
character that was typed by a user). For example, if a business rule
verifies that the data entered by a user is formatted in a specific
way, it's usually not a great experience to yield a validation error
before the user has finished typing. Instead, it's often better to
wait until the user has significantly interacted with a UI control
before running business logic.
For this reason, I propose to add a new type of binding to the
javafx.beans.binding.Bindings class:
void bindBidirectional(Property<T> target, Property<T> source,
UpdateSourceTrigger trigger)
UpdateSourceTrigger is an enumeration that allows developers to
specify the condition on which changes of the target property will
update the source property. Its values are:
DEFAULT: Updates the source property on every change (this is the
default behavior of bidirectional bindings).
FOCUS: Updates the source property when the UI control loses input
focus.
ACTION: Updates the source property when the UI control loses input
focus or when it receives an ActionEvent (in the case of TextField,
this corresponds to the ENTER key).
Note that this setting only applies to changes of the target property.
When the source property is changed instead, the target property is
always immediately updated.
Any feedback on this proposal is appreciated.
