java - JavaFX:如何在列表中绑定(bind)多个属性？

我有一个SimpleElement类，其中有一个权重字段，第二个类有一个SimpleElement列表，并且一个权重字段取决于列表中包含的所有其他SimpleElement的权重之和。有谁知道如何通过绑定来做到这一点？

我的代码：

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

public class SimpleElement {

    IntegerProperty weight;

    public SimpleElement() {
        weight = new SimpleIntegerProperty();
    }

    public int getWeight() {
        return weight.get();
    }

    public void setWeight(int weight) {
        this.weight.set(weight);
    }

    public IntegerProperty weightProperty() {
        return weight;
    }
}

和

import java.util.ArrayList;
import java.util.List;
import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;

public class RootElement {

    List<SimpleElement> elements;
    IntegerProperty weight;

    public RootElement() {
        elements = new ArrayList<>();
        weight = new SimpleIntegerProperty();
    }

    public void addelements(SimpleElement element) {
        elements.add(element);
    }
}

最佳答案

可以重写RootElement类以创建每个SimpleElement的绑定，并将它们加起来：

public class RootElement {
    List<SimpleElement> elements;
    IntegerProperty weight;
    NumberBinding binding;

    public RootElement() {
        elements = new ArrayList<>();
        weight = new SimpleIntegerProperty();
    }

    public void addelements(SimpleElement element) {
        elements.add(element);

        if (binding == null) {
            binding = element.weightProperty().add(0);
        } else {
            binding = binding.add(element.weightProperty());
        }

        weight.bind(binding);
    }

    public Integer getWeight() {
        return weight.get();
    }

    public ReadOnlyIntegerProperty weightProperty() {
        return weight;
    }
}

用法示例：

public static void main(String[] args) {
    SimpleElement se1 = new SimpleElement();
    SimpleElement se2 = new SimpleElement();
    SimpleElement se3 = new SimpleElement();
    RootElement root = new RootElement();

    root.addelements(se1);
    root.addelements(se2);
    root.addelements(se3);

    root.weightProperty().addListener(new ChangeListener<Number>() {
        @Override
        public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
            System.out.println(newValue);
        }
    });

    se1.setWeight(3);
    se2.setWeight(2);
    se1.setWeight(4);
}

上面代码的执行产生：

3

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