如何在JavaFX中实现派生的只读属性/值？

Question

Suppose I have an object, representing database table and it has property, denoting current selected row:

class MyTable {

   private IntegerProperty currentRow ...

   public IntegerProperty currentRowProperty() {
      return currentRow;
   }

   public int getCurrentRow() {
      return currentRow.get();
   }

   public void setCurrentRow(int newValue) {
      currentRow.setValue(newValue);
   }
}

Now I wish to have additional explicit read-only entity to denote, whether the row can be moved to previous (to bind to "previous" button).

If I implement it with Binding

class MyTable {

   private BooleanBinding previousExist = currentRowProperty().greaterThan(0);

   public BooleanBinding previousExistBinding() {
      return previousExist;
   }

   public boolean isPreviousExist() {
      return previousExist.get();
   }
}

I will violate JavaFX property pattern, because returned class will be binding, not property.

Hence, I need to wrap result into property, but how?

If I write

class MyTable {
   private ReadOnlyBooleanPropertyBase previousExist = new ReadOnlyBooleanPropertyBase() {
      @Override
      public boolean get() {
         return getIndex() >= 0;
      }
      ...
   }
}

I will be unable to rely on change reporting and will be required to listen index changes explicitly and fire them forward.

So, how to implement?

Answer 1

ReadOnlyBooleanWrapper is to use:

private ReadOnlyBooleanWrapper previousExist;
{
   ReadOnlyBooleanWrapper ans = new ReadOnlyBooleanWrapper();
   ans.bind( currentRowProperty().greaterThan(0) );
   previousExist = ans;
}

public ReadOnlyBooleanProperty previousExist() {
   return previousExist.getReadOnlyProperty();
}

public boolean isPreviousExist() {
   return previousExist().get();
}