JavaFX 8 MapProperty 解除绑定(bind)不起作用？

Question

谁能解释一下这是一个错误还是我在 JavaFX MapProperty 绑定(bind)中遗漏了什么？

场景:两个 MapProperty 实例 - 主实例和子实例。

1. 首先，我们将 child 绑定(bind)到 master
2. 然后我们在 master 中存储一些值
3. 解除子进程与master的绑定(bind)
4. 清楚的 child
5. 两个实例都是空的 - 为什么？
6. 在 child 中存储一些值
7. 两个实例包含相同的值 - 为什么？

代码:

public static void main(String[] args) {

    MapProperty<String, Object> master = new SimpleMapProperty<String, Object>(
            FXCollections.observableMap(new HashMap<String, Object>()));
    MapProperty<String, Object> child = new SimpleMapProperty<String, Object>(
            FXCollections.observableMap(new HashMap<String, Object>()));

    child.bind(master);

    master.put("k1", "v1");

    System.out.println("Java version: " + System.getProperty("java.version"));
    System.out.println("OS version  : " + System.getProperty("os.name") + " - " + System.getProperty("os.arch"));
    System.out.println("------------");
    System.out.println("master: " + master);
    System.out.println("child : " + child);

    // Isn't this supposed to stop change listener ?????
    child.unbind();
    child.clear();

    System.out.println("------------");
    System.out.println("master: " + master);
    System.out.println("child : " + child);

    child.put("k2", "v2");

    System.out.println("------------");
    System.out.println("master: " + master);
    System.out.println("child : " + child);

}

输出:

run:
Java version: 1.8.0_45
OS version  : Windows 7 - amd64
------------
master: MapProperty [value: {k1=v1}]
child : MapProperty [bound, invalid]
------------
master: MapProperty [value: {}]
child : MapProperty [value: {}]
------------
master: MapProperty [value: {k2=v2}]
child : MapProperty [value: {k2=v2}]
BUILD SUCCESSFUL (total time: 0 seconds)

Answer 1

MapProperty 的值是一个 ObservableMap，而不是 ObservableMap 的内容。

执行这段代码

MapProperty<String, Object> master = new SimpleMapProperty<String, Object>(
        FXCollections.observableMap(new HashMap<String, Object>()));
MapProperty<String, Object> child = new SimpleMapProperty<String, Object>(
        FXCollections.observableMap(new HashMap<String, Object>()));

ObservableMap<String, Object> childMap = child.get();
ObservableMap<String, Object> masterMap = master.get();

System.out.println("before binding: " + ((childMap == masterMap) ? "childMap == masterMap" : "childMap != masterMap"));

child.bind(master);

childMap = child.get();
masterMap = master.get();

System.out.println("after binding: " + ((childMap == masterMap) ? "childMap == masterMap" : "childMap != masterMap"));

child.unbind();
System.out.println("after unbinding: " + ((childMap == masterMap) ? "childMap == masterMap" : "childMap != masterMap"));   

显示绑定(bind)后，child 和 main 中的 ObservableMap 是同一个对象，因为属性包装了 map 而不是它的内容:

before binding: childMap != masterMap
after binding: childMap == masterMap
after unbinding: childMap == masterMap

---

要绑定(bind) map 的内容，请改用bindContent。执行中

MapProperty<String, Object> master = new SimpleMapProperty<String, Object>(
        FXCollections.observableMap(new HashMap<String, Object>()));
MapProperty<String, Object> child = new SimpleMapProperty<String, Object>(
        FXCollections.observableMap(new HashMap<String, Object>()));

child.bindContent(master);

master.put("k1", "v1");

System.out.println("Java version: " + System.getProperty("java.version"));
System.out.println("OS version  : " + System.getProperty("os.name") + " - " + System.getProperty("os.arch"));
System.out.println("------------");
System.out.println("master: " + master);
System.out.println("child : " + child);

child.unbindContent(master);
child.clear();

System.out.println("------------");
System.out.println("master: " + master);
System.out.println("child : " + child);

child.put("k2", "v2");

System.out.println("------------");
System.out.println("master: " + master);
System.out.println("child : " + child);

给出以下结果:

Java version: 1.8.0_45
OS version  : Windows 7 - amd64
------------
master: MapProperty [value: {k1=v1}]
child : MapProperty [value: {k1=v1}]
------------
master: MapProperty [value: {k1=v1}]
child : MapProperty [value: {}]
------------
master: MapProperty [value: {k1=v1}]
child : MapProperty [value: {k2=v2}]