JavaFX：双向绑定的初始值

JavaFX: Initial value of bidirectional binding

当我对这两个属性进行绑定时会发生什么？

ObjectProperty<Object> propertyA = new SimpleObjectProperty<>();
ObjectProperty<Object> propertyB = new SimpleObjectProperty<>();

propertyA.set(new ObjectA());
propertyB.set(new ObjectB());

Bindings.bindBidirectional(propertyA, propertyB);

如果两个属性应该持有相同的对象引用，那么在这个绑定之后，两个属性是否都持有 ObjectA 或 ObjectB 的引用？

当你打电话时：

Bindings.bindBidirectional(propertyA, propertyB);

propertyA 的值将被设置为 propertyB 的值。

所以在这种情况下，由于 propertyB 已经引用了 ObjectB，在调用之后，两个属性都将引用：ObjectB

测试代码

import javafx.beans.binding.Bindings;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;

public class HellBound {
    public static void main(String[] args) {
        ObjectProperty<Object> propertyA = new SimpleObjectProperty<>();
        ObjectProperty<Object> propertyB = new SimpleObjectProperty<>();

        propertyA.set(new ObjectA());
        propertyB.set(new ObjectB());

        Bindings.bindBidirectional(propertyA, propertyB);

        System.out.println("propertyA = " + propertyA);
        System.out.println("propertyB = " + propertyB);
    }

    private static class ObjectA {
    }

    private static class ObjectB {
    }
}

测试输出

propertyA = ObjectProperty [value: appCC.xyzzy.HellBound$ObjectB@7c3df479]
propertyB = ObjectProperty [value: appCC.xyzzy.HellBound$ObjectB@7c3df479]

绑定实现源码

注意调用 property1.setValue(property2.getValue());:

public static <T> BidirectionalBinding bind(Property<T> property1, Property<T> property2) {
    checkParameters(property1, property2);
    final BidirectionalBinding binding =
            ((property1 instanceof DoubleProperty) && (property2 instanceof DoubleProperty)) ?
                    new BidirectionalDoubleBinding((DoubleProperty) property1, (DoubleProperty) property2)
            : ((property1 instanceof FloatProperty) && (property2 instanceof FloatProperty)) ?
                    new BidirectionalFloatBinding((FloatProperty) property1, (FloatProperty) property2)
            : ((property1 instanceof IntegerProperty) && (property2 instanceof IntegerProperty)) ?
                    new BidirectionalIntegerBinding((IntegerProperty) property1, (IntegerProperty) property2)
            : ((property1 instanceof LongProperty) && (property2 instanceof LongProperty)) ?
                    new BidirectionalLongBinding((LongProperty) property1, (LongProperty) property2)
            : ((property1 instanceof BooleanProperty) && (property2 instanceof BooleanProperty)) ?
                    new BidirectionalBooleanBinding((BooleanProperty) property1, (BooleanProperty) property2)
            : new TypedGenericBidirectionalBinding<T>(property1, property2);
    property1.setValue(property2.getValue());
    property1.addListener(binding);
    property2.addListener(binding);
    return binding;
}

其他问题的答案

I'm just wondering why the javadoc doesn't tell us this kind of useful information.

因为javadoc是人写的，不是神。有时人类会做出难以理解的疏漏。也许神也这样做:-)

我同意 Javadoc 中应该包含有用的信息。

可以提交错误报告以改进文档（http://bugreport.java.com). Or a post to the openjfx-dev developer list might get a developer with commit privileges to improve it. You could submit a patch yourself, but, for most people, unless they are already a JDK committer who has signed the OCA，这可能不值得。

I'm assuming this should also be the same for ObservableLists, such that Bindings.bindContentBidirectional() should work in the same way?

是的，该方法的源代码如下：

list1.setAll(list2);

JavaFX：双向绑定的初始值

JavaFX: Initial value of bidirectional binding

data-binding

javafx

javafx-bindings