JavaFX - 将ObjectProperty绑定到另一个ObjectProperty中的成员？

Question

我有一个名为Tree

public class Tree 
{ 
    private Color c; 

    public Color getColor() 
    { 
     return c; 
    } 
} 

类我有一个ObjectProperty ...

ObjectProperty<Tree> importantTree = new SimpleObjectProperty(); 

我要让Color类型总是等于importantTree.get().getColor()的另一个ObjectProperty。每当Tree发生变化时，我都希望其他ObjectProperty更改为Tree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

只需使用一个绑定：

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. 

你也可以做

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

如果你喜欢。