JavaFX - 将 ObjectProperty 绑定(bind)到另一个 ObjectProperty 内的成员？

Question

我有一个名为Tree的类

public class Tree
{
    private Color c;

    public Color getColor()
    {
        return c;   
    }   
}

我有一个ObjectProperty...

ObjectProperty<Tree> importantTree = new SimpleObjectProperty();

我想创建另一个 Color 类型的 ObjectProperty，它始终等于 importantTree.get().getColor()。每当树发生变化时，我希望其他 ObjectProperty 更改为该树的颜色。

例如。

ObjectProperty<Tree> importantTree = new SimpleObjectProperty();
ObjectProperty<Color> importantTreesColor = ... 


Tree a = new Tree(Color.RED);
Tree b = new Tree(Color.GREEN);

importantTree.set(a);
System.out.println(importantTreesColor.get()); // This should print RED.

importantTree.set(b);
System.out.println(importantTreesColor.get()); // This should print GREEN.

Answer 1

只需使用绑定(bind):

ObjectProperty<Tree> importantTree = new SimpleObjectProperty();
Binding<Color> importantTreesColor = Bindings.createObjectBinding(() -> 
    importantTree.get() == null ? null : importantTree.get().getColor(),
    importantTree);

Tree a = new Tree(Color.RED);
Tree b = new Tree(Color.GREEN);

importantTree.set(a);
System.out.println(importantTreesColor.getValue()); // Prints RED.

importantTree.set(b);
System.out.println(importantTreesColor.getValue()); // Prints GREEN.

你也可以这样做

Binding<Color> importantTreesColor = new ObjectBinding<Color>() {
    { bind(importantTree); }
    @Override
    protected Color computeValue() {
        return importantTree.get()==null ? null : importantTree.get().getColor();
    }
};

如果你愿意的话。