JavaFX - 将属性绑定到可观察Collection中每个元素的属性

Question

是否存在将BooleanProperty绑定到ObservableList中每个元素的连接的任何方法？

ObservableList<BooleanProperty> list;
list = FXCollections.observableList(new ArrayList<BooleanProperty>));
BooleanProperty emptyProperty = new SimpleBooleanProperty();
emptyProperty.bind(Bindings.conunction(list));`

有这样的方法:

static BooleanBinding conjunction(ObservableList<BooleanProperty> op)

Answer 1

JavaFX 2.2平台中没有定义连接 api.

您可以通过继承BooleanBinding来创建ConjunctionBooleanBinding(aka AllTrueBinding).

接受新类的构造函数中的ObservableList,并在重写的computeValue方法中使用低级绑定api,根据逻辑上将所有布尔值放在一起来设置绑定值.

这是一个示例实现.样本可以进一步进行性能优化并使用WeakReferences,因此不需要手动处理.

import javafx.beans.binding.BooleanBinding;
import javafx.beans.property.BooleanProperty;
import javafx.collections.*;

public class AllTrueBinding extends BooleanBinding {
  private final ObservableList<BooleanProperty> boundList;
  private final ListChangeListener<BooleanProperty> BOUND_LIST_CHANGE_LISTENER =
    new ListChangeListener<BooleanProperty>() {
      @Override public void onChanged(
             ListChangeListener.Change<? extends BooleanProperty> change
          ) {
        refreshBinding();
      }
    };
  private BooleanProperty[] observedProperties = {};

  AllTrueBinding(ObservableList<BooleanProperty> booleanList) {
    booleanList.addListener(BOUND_LIST_CHANGE_LISTENER);
    boundList = booleanList;
    refreshBinding();
  }

  @Override protected boolean computeValue() {
    for (BooleanProperty bp: observedProperties) {
      if (!bp.get()) {
        return false;
      }
    }

    return true;
  }

  @Override public void dispose() {
    boundList.removeListener(BOUND_LIST_CHANGE_LISTENER);
    super.dispose();
  }

  private void refreshBinding() {
    super.unbind(observedProperties);
    observedProperties = boundList.toArray(new BooleanProperty[0]);
    super.bind(observedProperties);
    this.invalidate();
  }
}

这是一个测试工具来演示它是如何工作的:

import java.util.*;
import javafx.beans.property.*;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;

public class ListBindingTest {
  final BooleanProperty a = new SimpleBooleanProperty(true);
  final BooleanProperty b = new SimpleBooleanProperty(true);
  final BooleanProperty c = new SimpleBooleanProperty(true);
  final BooleanProperty d = new SimpleBooleanProperty(true);
  final ObservableList<BooleanProperty> booleanList =
    FXCollections.observableArrayList(a, b, c, d);

  public static void main(String[] args) {
    new ListBindingTest().test();
  }

  private void test() {
    AllTrueBinding at = new AllTrueBinding(booleanList);

    System.out.println(at.get() + forArrayString(booleanList));

    b.set(false);
    System.out.println(at.get() + forArrayString(booleanList));

    b.set(true);
    System.out.println(at.get() + forArrayString(booleanList));

    booleanList.add(new SimpleBooleanProperty(false));
    System.out.println(at.get() + forArrayString(booleanList));

    booleanList.remove(3, 5);
    System.out.println(at.get() + forArrayString(booleanList));

    at.dispose();
  }  

  private String forArrayString(List list) {
    return " for " + Arrays.toString(list.toArray());
  }
}

Answer 2

您可以按如下方式轻松实现该方法:

public static BooleanBinding conjunction(ObservableList<BooleanProperty> list){   
  BooleanBinding and = new SimpleBooleanProperty(true).and(list.get(0));
  for(int i = 1; i < list.size(); i++){
    and = and.and(list.get(i));   
  }
  return and;
}