list - JavaFX - 将属性绑定(bind)到可观察集合中每个元素的属性

Question

是否存在将 BooleanProperty 绑定(bind)到 ObservableList 中每个元素的连接的方法？

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

有没有这样的方法:

static BooleanBinding conjunction(ObservableList<BooleanProperty> op)

Answer 1

没有conjunction JavaFX 2.2 平台中定义的 api。

您可以通过子类化 BooleanBinding 创建一个 ConjunctionBooleanBinding (又名 AllTrueBinding) 。

接受ObservableList在新类的构造函数中，并使用 low level binding api在一个被覆盖的computeValue方法根据逻辑上将列表中的所有 bool 值组合在一起来设置绑定(bind)值。

这是一个示例实现。该示例可以进一步进行性能优化并利用WeakReferences，因此不需要手动配置。

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());
  }
}