无法在JavaFX中向ObservableList(UnsupportedOperationException)添加元素

Question

初始起点

我有一个List1000个Person对象,我想插入一个Extractor来监听任何Person对象中的属性更改(ObservableList稍后将附加到a TableView).

所以我的代码就像:

ObservableList<Person> observablePersons = FXCollections.observableList(personlist,
    personextractor);

错误信息

但是当我尝试向这个ObservableList observablePersons添加一个新人对象时,我遇到了这个错误:

run:
Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:148)
    at com.sun.javafx.collections.ObservableListWrapper.doAdd(ObservableListWrapper.java:101)
    at javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:151)
    at java.util.AbstractList.add(AbstractList.java:108)
    at test.listchangelistener.listChangeDemo.main(listChangeDemo.java:72)
Java Result: 1

您能否告诉我为什么会遇到此错误消息？我的java版本是jdk1.8.0_91(32位)

人类

package test.listchangelistener;

import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

class Person {

    private final IntegerProperty age = new SimpleIntegerProperty();
    private final StringProperty name = new SimpleStringProperty();

    public Person(String name, Integer age) {
        setName(name);
        setAge(age);
    }

    public int getAge() {
        return age.get();
    }

    public final void setAge(int value) {
        age.set(value);
    }

    public IntegerProperty ageProperty() {
        return age;
    }

    public String getName() {
        return name.get();
    }

    public final void setName(String value) {
        name.set(value);
    }

    public StringProperty nameProperty() {
        return name;
    }

    @Override
    public String toString() {
        return "Person{" + "age=" + age.get() + ", name=" + name.get() + '}';
    }

}

测试代码

package test.listchangelistener;

import java.util.Arrays;
import java.util.List;
import javafx.beans.Observable;
import javafx.collections.FXCollections;
import javafx.collections.ListChangeListener;
import javafx.collections.ObservableList;
import javafx.util.Callback;


public class listChangeDemo {
    public static void main(String[] args) {

        Person p1 = new Person("Ted", 26);
        Person p2 = new Person("Anne", 19);

        // just a simple list
        List<Person> persons = Arrays.asList(p1, p2);

        // extractor to observe change of person properties
        Callback<Person, Observable[]> extractor = (Person p) -> {
            return new Observable[]{
                p.ageProperty(),
                p.nameProperty()
            };
        };

        // make list observable and attach extractor
        ObservableList<Person> observablePersons = FXCollections.observableList(persons, extractor);

        // create listchangeListener for observableList
        ListChangeListener listener = (ListChangeListener) (ListChangeListener.Change c) -> {
            while (c.next()) {
                if (c.wasAdded()) {
                    System.out.println("these were added: ");

                    List addedSubList = c.getAddedSubList();
                    addedSubList.forEach((Object t) -> {
                        System.out.println("added Person: " + t);
                    });
                } else if (c.wasRemoved()) {
                    System.out.println("these were removed");

                    List removedSubList = c.getRemoved();
                    removedSubList.forEach((Object t) -> {
                        System.out.println("removed Person: " + t);
                    });

                } else if (c.wasUpdated()) {
                    System.out.println("these were updated");

                    System.out.println("Updated elements are: "
                            + c.getList().subList(c.getFrom(), c.getTo()));
                }
            }
        };

        // attach listchangeListener to observableList
        observablePersons.addListener(listener);

        // testing changes
        observablePersons.add(new Person("Siegfried", 10));

    }
}

Answer 1

问题来自于您的支持的创建List:

List<Person> persons = Arrays.asList(p1, p2);

如果你看一下Arrays.asList的javadoc:

返回由指定数组支持的固定大小的列表.

仔细看看你得到了UnsupportedOperationException,因为List.add()是一个可选操作:

抛出:UnsupportedOperationException - 如果此列表不支持add操作.

您可以将支持列表的创建更新为:

List<Person> persons = new ArrayList<Person>(Arrays.asList(p1, p2));

不同之处在于返回的ArrayList是传递的精确,独立的副本,因此在这种情况下上述限制不再有效.

您还可以查看这个深入解释此主题的问题:

java中Arrays.asList(array)与新ArrayList <Integer>(Arrays.asList(ia))的区别