JavaFX has support for extending containers and controls. Most of us writing these extensions want them to be FXML friendly. JavaFX provides a number of annotations to help improve FXML support and you should definitely have them on your controls.

The annotations are as follows:

@DefaultProperty

@NamedArg

@IDProperty

Lets have a look at each of these annotations and their usage in details:

@DefaultProperty

Specifies a property to which child element(s) will be added or set when an explicit child property tag is not defined in FXML.

For example:

Pane has a default property defined as “children”, which corresponds to the children property.

@DefaultProperty("children") public class Pane extends Region { ... }

ImageView has default property defined as “image”, which corresponds to the image property.

@DefaultProperty("image") public class ImageView extends Node { ... }

Consider the following FXML:

<Pane fx:id=”pane”> <children> <ImageView> <image> <Image url=""> </image> </ImageView> </children> </Pane>

Since @DefaultProperty is defined for both Pane and ImageView , we can re-write the FXML as:

<Pane fx:id=”pane”> <ImageView> <Image url=""> </ImageView> </Pane>

There are a few things to keep in mind while annotating a class with @DefaultProperty :

Class should define a public default constructor

Class should not have any constructor with parameters annotated with @NamedArg

@NamedArg

Used to define arguments for a class which will be used by the FXMLLoader to instantiate the class when its used inside a FXML.

For example, one of the constructor in Image is declared as:

public Image(@NamedArg("url") String url) { ... }

This indicates that an Image can be declared in FXML with a url property.

<ImageView> <Image url="/icon.png"/> </ImageView>

Just like @DefaultProperty , here are a few things you should keep in mind while annotating parameters with @NamedArg :

@NamedArg should be used to define properties which can be injected as parameters to the constructor.

should be used to define properties which can be injected as parameters to the constructor. If the properties annotated with @NamedArg are not provided in the FXML, the FXMLLoader will: Call the default constructor, if present. Call the parameterized constructor with null values.

are not provided in the FXML, the FXMLLoader will: @DefaultProperty and @NamedArg should not be used on the same class. In case they are used, @DefaultProperty will not work.

@IDProperty

Specifies a property which can be used by the FXMLLoader to set the value from fx:id . For all child classes of Node , it is mapped to the id property of Node .

In case a class extends from Node or any of its subclasses, you do not need to worry about this property. Classes which do not extend from Node and desire FXML support, needs to declare @IDProperty .

The following classes in JavaFX, which do not extend Node , use them:

ContextMent

MenuItem

Tab

TableColumnBase

ToolTip

At the time of writing this post, @IDProperty is still a private API and is present in com.sun.javafx.beans package. Therefore, all controls using this property will fail to compile under JDK 9 and later. There is an open issue to move it to the public javafx.beans package.

As I stated in the beginning of the post, these annotations should be used on every custom control. If you are extending a Node which has these annotations on them, you can choose to either skip or override them.

Lets make all controls FXML friendly!!!