JavaFx 8 双向绑定(bind)

Question

以下代码引发java.lang.RuntimeException:无法设置绑定(bind)值:

public class Test {

   public static void main( String[] args ) {
      final DoubleProperty amount = new SimpleDoubleProperty( 100_000.00 );
      final DoubleProperty rate   = new SimpleDoubleProperty();
      final DoubleProperty part   = new SimpleDoubleProperty();
      rate.bind( part.divide  ( amount.getValue()));
      part.bind( rate.multiply( amount.getValue()));
      rate.set( 0.025 );//<<----------------------------------- Here is the cause
      System.out.println( "Part: " + part.get());
      part.set( 1200 );
      System.out.println( "Rate: " + rate.get());
   }
}

使用Bindings.bindBidirectional可能是一个解决方案，但我不知道如何解决。

Answer 1

一个可能的解决方案是创建 InvalidationListeners - 不使用绑定(bind)。

它是如何工作的:

• 设置费率会导致费率无效。这是设置部分的时间，因此也是无效的。
• 依次设置速率不会再次触发 InvalidationListener。这就是它的定义方式。

.

public static void main(String[] args) {
    final DoubleProperty amount = new SimpleDoubleProperty(100_000.00);
    final DoubleProperty part = new SimpleDoubleProperty();
    final DoubleProperty rate = new SimpleDoubleProperty();

    part.addListener(new InvalidationListener() {
        @Override
        public void invalidated(Observable observable) {
            System.out.println("part is invalid");
            rate.set(part.get() / amount.get());
        }
    });

    rate.addListener(new InvalidationListener() {
        @Override
        public void invalidated(Observable observable) {
            System.out.println("rate is invalid");
            part.set(rate.get() * amount.get());
        }
    });

    System.out.println("setting rate");
    rate.set(0.025);
    System.out.println("Part: " + part.get()); //2500

    System.out.println("setting part");
    part.set(1200);
    System.out.println("Rate: " + rate.get()); //0.012
}

上面代码的输出是:

setting rate
rate is invalid
part is invalid
Part: 2500.0
setting part
part is invalid
rate is invalid
Rate: 0.012