可观察集合中的一些方法

以下例子均以list为例

• rotate()重新排序

  ObservableList<String> list = FXCollections.observableArrayList();  
  list.add("a");  
  list.add("c");  
  list.add("e");  
  list.add("b");  
  list.add("d");  
  // 从倒数第3个元素依此往后循环对列表元素进行排序  
  FXCollections.rotate(list, 3);  
  list.forEach(item -> System.out.print(item + " "));  
  System.out.println();  
  // 删除索引为1的元素  
  list.remove(1);  
  list.forEach(item -> System.out.print(item + " "));
  

  e b d a c
  e d a c

• Callback() 回调函数

  // 每次相list中添加元素时，会触发一次回调函数  
  ObservableList<SimpleStringProperty> list = FXCollections.observableArrayList(new Callback<SimpleStringProperty, Observable[]>() {
      /**  
     * 此方法返回值将作为list的每个值  
     * @param param  
     * @return  
     */
      @Override  
      public Observable[] call(SimpleStringProperty param) {
          if (param.getValue().equals("c")) {
              System.out.println("str1.set("c"); run into this method");
          }
          System.out.println("call : " + param.get());
          return new Observable[]{
              param
          };
      }
  });
  SimpleStringProperty str1 = new SimpleStringProperty("a");
  SimpleStringProperty str2 = new SimpleStringProperty("b");
  list.add(str1);
  list.add(str2);
  list.forEach(item -> System.out.print(item.get() + " "));
  System.out.println();
  list.addListener(new ListChangeListener<SimpleStringProperty>() {
      @Override  
      public void onChanged(Change<? extends SimpleStringProperty> c) {
          System.out.println("onChanged : " + c);
          while (c.next()) {
              System.out.println("c.wasUpdated() = " + c.wasUpdated());
          }
      }
  });
  // 重复地往集合中添加元素，只会调用一次call方法  
  list.add(str2);
  list.forEach(item -> System.out.print(item.get() + " "));
  System.out.println();
  str1.set("c");
  list.forEach(item -> System.out.print(item.get() + " "));
  

  call : a
  call : b
  a b
  onChanged : { [StringProperty [value: b]] added at 2 }
  c.wasUpdated() = false
  a b b
  onChanged : { updated at range [0, 1) }
  c.wasUpdated() = true
  c b b

• 反例(下面例子证明：如果在创建可观察列表时没有指定回调函数callback，则当集合中存储的数据发生变化时，不会触发集合对应监视属性的监听方法)

  ObservableList<SimpleStringProperty> list = FXCollections.observableArrayList();
  SimpleListProperty<SimpleStringProperty> listProperty = new SimpleListProperty<>(list);
  listProperty.addListener((ListChangeListener<SimpleStringProperty>) c -> {
      while (c.next()) {
          System.out.println("c.wasUpdated() = " + c.wasUpdated());
      }
  }
                          );
  SimpleStringProperty string1 = new SimpleStringProperty("aa");
  SimpleStringProperty string2 = new SimpleStringProperty("cc");
  listProperty.add(string1);
  listProperty.add(string2);
  // 此行无输出
  string1.set("bb");
  

  c.wasUpdated() = false
  c.wasUpdated() = false

• 将上面例子第一行改为

  ObservableList<SimpleStringProperty> list = FXCollections.observableArrayList(param -> new Observable[]{param});
  

  c.wasUpdated() = false
  c.wasUpdated() = false
  c.wasUpdated() = true

两个可观察列表双向绑定的另一种实现

SimpleStringProperty str1 = new SimpleStringProperty("aa");  
SimpleStringProperty str2 = new SimpleStringProperty("dd");  
ObservableList<SimpleStringProperty> list = FXCollections.observableArrayList(new Callback<SimpleStringProperty, Observable[]>() {  
    @Override  
    public Observable[] call(SimpleStringProperty param) {  
        System.out.println(Color.RED + "(list)call : " + param.get() + Color.RESET);  
        return new Observable[]{param};  
    }  
});  
ObservableList<SimpleStringProperty> list1 = FXCollections.observableList(list, new Callback<SimpleStringProperty, Observable[]>() {  
    @Override  
    public Observable[] call(SimpleStringProperty param) {  
        System.out.println(Color.BLUE + "(list1)call : " + param.get() + Color.RESET);  
        return new Observable[]{param};  
    }  
});  
list.addListener(new ListChangeListener<SimpleStringProperty>() {  
    @Override  
    public void onChanged(Change<? extends SimpleStringProperty> c) {  
        System.out.println(Color.RED + "(list)onChanged : " + c + Color.RESET);  
        while (c.next()) {  
            System.out.println(Color.RED + "c.wasUpdated() = " + c.wasUpdated() + Color.RESET);  
        }  
    }  
});  
list1.addListener(new ListChangeListener<SimpleStringProperty>() {  
    @Override  
    public void onChanged(Change<? extends SimpleStringProperty> c) {  
        System.out.println(Color.BLUE + "(list1)onChanged : " + c + Color.RESET);  
        while (c.next()) {  
            System.out.println(Color.BLUE + "c.wasUpdated()1 = " + c.wasUpdated() + Color.RESET);  
        }  
    }  
});  
list1.add(str1);  
list.forEach(item -> System.out.print(Color.RED + item.get() + " "));  
list1.forEach(item -> System.out.print(Color.BLUE + item.get() + " "));  
System.out.println();  
System.out.println(Color.MAGENTA + "-------------------------------------------------" + Color.RESET);  

list.add(str2);  
list.forEach(item -> System.out.print(Color.RED + item.get() + " "));  
list1.forEach(item -> System.out.print(Color.BLUE + item.get() + " "));  
System.out.println();  
System.out.println(Color.MAGENTA + "-------------------------------------------------" + Color.RESET);  

str1.set("cc");  
list.forEach(item -> System.out.print(Color.RED + item.get() + " "));  
list1.forEach(item -> System.out.print(Color.BLUE + item.get() + " "));  
System.out.println();  
System.out.println(Color.MAGENTA + "-------------------------------------------------" + Color.RESET);  

str2.set("bb");  
list.forEach(item -> System.out.print(Color.RED + item.get() + " "));  
list1.forEach(item -> System.out.print(Color.BLUE + item.get() + " "));  
System.out.println();  
System.out.println(Color.MAGENTA + "-------------------------------------------------" + Color.RESET);

(list1)call : aa
(list)call : aa
(list)onChanged : { [StringProperty [value: aa]] added at 0 }
c.wasUpdated() = false
(list1)onChanged : { [StringProperty [value: aa]] added at 0 }
c.wasUpdated()1 = false
aa aa
(list)call : dd
(list)onChanged : { [StringProperty [value: dd]] added at 1 }
c.wasUpdated() = false
aa dd aa dd
(list1)onChanged : { updated at range [0, 1) }
c.wasUpdated()1 = true
(list1)onChanged : { updated at range [0, 1) }
c.wasUpdated() = true
cc dd cc dd
(list)onChanged : { updated at range [1, 2) }
c.wasUpdated() = true
cc bb cc bb