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.
