Question

我有一个具有以下属性的类：

public class Member {
    private LongProperty version;

    private LongProperty id;

    private StringProperty name;

    private StringProperty surname;

    private StringProperty bornname;

    private StringProperty photo;

    private ObjectProperty<Age> age;

    private ObjectProperty<Sex> sex;
}

问题是，当我在这个对象上添加Change Listener时：

{
    private ObjectProperty<Member> member;

    public void addMemberChangeListener() {
        this.member.addListener((observable, oldValue, newValue) -> {
            if (newValue != null) {
                (...)
      }
    }
}

更改属性值时，不会通知更改侦听器。还有其他方法可以通知侦听器有关实现标准Observer模式的更改属性吗？

Answer 1

如果要添加在属于Member实例的任何属性发生更改时收到通知的单个侦听器，您可以执行以下操作：

Member member = new Member();

ChangeListener<Object> listener = (obs, oldValue, newValue) -> 
    System.out.println(obs + " changed from " + oldValue + " to " + newValue);

Stream.of(member.versionProperty(), member.idProperty(), member.nameProperty() /*, ... */)
    .forEach(p -> p.addListener(listener));

请注意，具体属性类包含一个构造函数，该构造函数接受拥有bean和属性的名称，因此如果要支持这种使用，可能需要使用这些构造函数：

public class Member {

    private final LongProperty version = new SimpleLongProperty(this, "version");
    private final StringProperty name = new SimpleStringProperty(this, "name");

    // ...
}

然后您可以在更改侦听器中利用它：

ChangeListener<Object> listener = (obs, oldValue, newValue) -> 
    System.out.println(((Property<?>)obs).getName() + " changed from " + oldValue + " to " + newValue);

只是评论：根据我的经验，需要这种情况很少见（充其量）。您通常（总是？）发现为每个属性注册不同的侦听器更方便，因为通常在更改属性时要采取的操作取决于更改的属性。在其他情况下，无论如何通常都会有更优雅的解决方案。

Answer 2

属性侦听器在更改值memberProperty.setValue(otherMember)时触发，而不是在修改其值memberProperty.getValue().setId(0)的某些属性时触发

尝试使用 PropertyChangeSupport

示例：

public class Member
{

    private final PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    private long id;
    private String name;

    public void addChangeListener(PropertyChangeListener listener)
    {
        this.pcs.addPropertyChangeListener(listener);
    }

    public void removeChangeListener(PropertyChangeListener listener)
    {
        this.pcs.removePropertyChangeListener(listener);
    }

    public void setId(long newId)
    {
        long oldId = this.id;
        this.id = newId;
        pcs.firePropertyChange("id", oldId, newId);
    }

    public void setName(String newName)
    {
        String oldName = this.name;
        this.name = newName;
        pcs.firePropertyChange("name", oldName, newName);
    }

}

使用：

Member member = new Member();

member.addChangeListener((evt) ->
{
    System.out.println("Changed "
            + evt.getPropertyName()
            + ": " + evt.getOldValue()
            + " -> " + evt.getNewValue());
});

member.setId(15);
member.setName("Maria");
member.setName("Ana");

输出：

Changed id: 0 -> 15
Changed name: null -> Maria
Changed name: Maria -> Ana

通知。更改ObservableProperties

2 个答案: