javafx FXML and Controllers Instance creation in FXML
Example
The following class is used to demonstrate, how instances of classes can be created:
JavaFX 8
The annotation in Person(@NamedArg("name") String name) has to be removed, since the @NamedArg annotation is unavailable.
package fxml.sample;
import javafx.beans.NamedArg;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
public class Person {
public static final Person JOHN = new Person("John");
public Person() {
System.out.println("Person()");
}
public Person(@NamedArg("name") String name) {
System.out.println("Person(String)");
this.name.set(name);
}
public Person(Person person) {
System.out.println("Person(Person)");
this.name.set(person.getName());
}
private final StringProperty name = new SimpleStringProperty();
public final String getName() {
System.out.println("getter");
return this.name.get();
}
public final void setName(String value) {
System.out.println("setter");
this.name.set(value);
}
public final StringProperty nameProperty() {
System.out.println("property getter");
return this.name;
}
public static Person valueOf(String value) {
System.out.println("valueOf");
return new Person(value);
}
public static Person createPerson() {
System.out.println("createPerson");
return new Person();
}
}
Assume the Person class has already been initialized before loading the fxml.
A note on imports
In the following fxml example the imports section will be left out. However the fxml should start with
<?xml version="1.0" encoding="UTF-8"?>
followed by an imports section importing all classes used in the fxml file. Those imports are similar to non-static imports, but are added as processing instructions. Even classes from the java.lang package need to be imported.
In this case the following imports are should be added:
<?import java.lang.*?>
<?import fxml.sample.Person?>
JavaFX 8
@NamedArg annotated constructor
If there is a constructor where every parameter is annotated with @NamedArg and all values of the @NamedArg annotations are present in the fxml, the constructor will be used with those parameters.
<Person name="John"/>
<Person xmlns:fx="http://javafx.com/fxml">
<name>
<String fx:value="John"/>
</name>
</Person>
Both result in the following console output, if loaded:
Person(String)
No args constructor
If there is no suitable @NamedArg annotated constructor is available, the constructor that takes no parameters will be used.
Remove the @NamedArg annotation from the constructor and try loading.
<Person name="John"/>
This will use the constructor without parameters.
Output:
Person()
setter
fx:value attribute
The fx:value attribute can be used to pass it's value to a static valueOf method taking a String parameter and returning the instance to use.
Example
<Person xmlns:fx="http://javafx.com/fxml" fx:value="John"/>
Output:
valueOf
Person(String)
fx:factory
The fx:factory attribute allows creation of objects using arbitrary static methods that do not take parameters.
Example
<Person xmlns:fx="http://javafx.com/fxml" fx:factory="createPerson">
<name>
<String fx:value="John"/>
</name>
</Person>
Output:
createPerson
Person()
setter
<fx:copy>
Using fx:copy a copy constructor can be invoked. Specifying the fx:id of another The source attribute of the tag will invoke the copy constructor with that object as parameter.
Example:
<ArrayList xmlns:fx="http://javafx.com/fxml">
<Person fx:id="p1" fx:constant="JOHN"/>
<fx:copy source="p1"/>
</ArrayList>
Output
Person(Person)
getter
fx:constant
fx:constant allows getting a value from a static final field.
Example
<Person xmlns:fx="http://javafx.com/fxml" fx:constant="JOHN"/>
won't produce any output, since this just references JOHN which was created when initializing the class.
