Compiled expressions

FXML 2.0 supports compiled expressions for one-time evaluation, observation, and bindings. These expressions are implemented as intrinsic markup extensions and compiled to specialized code by the FXML compiler.

Markup extension	Prefix notation	Usage
`fx:Evaluate`	`$source`	value supplier, property consumer
`fx:Observe`	`${source}`	value supplier, property consumer
`fx:Synchronize`	`#{source}`	property consumer

{fx:Evaluate} has the lowest runtime overhead, since no listener maintenance is required after the initial assignment. {fx:Observe} and {fx:Synchronize} may require listeners or additional generated code to keep the target synchronized with the source.

Setting up a binding

Here’s how a simple binding is specified in FXML 2.0, using different but equivalent notations:

com/sample/MyControl.fxml

<VBox xmlns="http://javafx.com/javafx" xmlns:fx="http://jfxcore.org/fxml/2.0"
      fx:subclass="com.sample.MyControl">
    <!-- fx:Observe markup extension with source path -->
    <Button text="{fx:Observe path=caption}"/>

    <!-- 'path' is the default property of the fx:Observe markup extension, so it can be omitted -->
    <Button text="{fx:Observe caption}"/>

    <!-- Prefix notation, similar to FXML 1.0 -->
    <Button text="${caption}"/>
</VBox>

com/sample/MyControl.java

public class MyControl extends MyControlBase {
    private final StringProperty caption = new SimpleStringProperty("Click me");

    public StringProperty captionProperty() {
        return caption;
    }

    public MyControl() {
        initializeComponent();
    }
}

Applying expressions to properties

When an intrinsic expression is assigned to a property (so it acts as a property consumer), the following operations are performed on the target property:

Markup extension	Prefix notation	Operation
`{fx:Evaluate source}`	`$source`	assign the resolved value once
`{fx:Observe source}`	`${source}`	`Property.bind(source)`
`{fx:Synchronize source}`	`#{source}`	`Property.bindBidirectional(source)`
`{fx:Evaluate ..source}`	`$..source`	`Collection.addAll(source)` `Map.putAll(source)`
`{fx:Observe ..source}`	`${..source}`	`ListProperty.bindContent(source)` `SetProperty.bindContent(source)` `MapProperty.bindContent(source)`
`{fx:Synchronize ..source}`	`#{..source}`	`ListProperty.bindContentBidirectional(source)` `SetProperty.bindContentBidirectional(source)` `MapProperty.bindContentBidirectional(source)`

Since path is the default property of all intrinsic expression extensions, {fx:Observe path=source} and {fx:Observe source} are equivalent.

This documentation will use the prefix notation in most code samples.

Compiled expressions

Setting up a binding

Applying expressions to properties

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