JavaBeans属性适配器如何工作? [英] How does JavaBeans Property Adapter work?

问题描述

如果我遵循

What I'm trying to do works fine if I follow the JavaFX property definition described here. Now, instead, I want to define properties from Java Beans objects using Java Beans Property Adapter. Since there is no documentation I can't figure out how it works.

假设我有一个简单的POJO类:

Suppose I have a simple POJO class:

public class Person {
    private String name;

    public String getName() {
        return name;
    }

    public void setName( String name ) {
        this.name = name;
    }
}

和一个PersonProperty:

and a PersonProperty:

public class PersonProperty {
    private Person person = new Person();

    private JavaBeanStringProperty name;

    public PersonProperty() throws NoSuchMethodException {
        name = JavaBeanStringPropertyBuilder.create().bean( person ).name( "name" ).build();
    }

    public Person getPerson() {
        return person;
    }

    public void setPerson( Person person ) {
        this.person = person;
    }

    public JavaBeanStringProperty nameProperty() {
        return name;
    }
}

最后是一个测试:

public void personTest() throws NoSuchMethodException {
    PersonProperty pp = new PersonProperty();

    pp.getPerson().setName( "A" );
    pp.getPerson().setName( "B" );

    pp.nameProperty().addListener( new ChangeListener<String>() {
        @Override
        public void changed( ObservableValue<? extends String> ov, String t, String t1 ) {
            System.out.println( "from " + t + " to " + t1 );
        }
    } );

    pp.getPerson().setName( "C" );
    pp.getPerson().setName( "D" );
}

我希望看到:

from B to C
from C to D

相反，什么也没有出现.

Instead nothing appears.

如果我在personTest末尾添加pp.nameProperty().set("E")，我会得到from B to E

If I add pp.nameProperty().set("E") at the end of personTest I get from B to E

推荐答案

我认为这里的问题是Person确实是POJO，但不是JavaBean:它缺少PropertyChangeListeners的钩子. Java不会神奇地知道Person#name何时更改.相反，JavaFX适配器将寻找一种添加PropertyChangeListener并侦听名为"name"的属性的事件的方法.如果将PropertyChangeSupport实例添加到Person类，它将按预期工作:

I think the issue here is that Person is indeed a POJO, but not a JavaBean: It is missing the hooks for PropertyChangeListeners. Java will not magically know when Person#name changes. Instead, the JavaFX adapter will look for a way to add a PropertyChangeListener and listen to events for a property called 'name'. If you add a PropertyChangeSupport instance to your Person class it will work as expected:

public class Person {
    private String name;
    private PropertyChangeSupport _changeSupport;

    public Person() {
        _changeSupport = new PropertyChangeSupport(this);
    }

    public String getName() {
        return name;
    }

    public void setName( String name ) {
        final String prev = this.name;
        this.name = name;
        _changeSupport.firePropertyChange("name", prev, name);
    }

    public void addPropertyChangeListener(final PropertyChangeListener listener) {
        _changeSupport.addPropertyChangeListener(listener);
    }
}

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