在TornadoFX中，如何使用objectBinding将BigDecimal属性绑定到另一个BigDecimal属性？

Question

I'm trying to create a binded BigDecimal property that is a calculation of two other BigDecimal properites, like this:

val caculatedProperty: ObjectProperty<BigDecimal> = objectBinding<Any, BigDecimal>(sumProperty, discountProperty) { ... }

...like I would do with StringProperty or IntegerProperty , and it would otherwise work without issues. However, this time I get a type mismatch: it expects ObjectProperty<BigDecimal> , but receives ObjectBinding<BigDecimal?> .

What's the problem here? Did I use the objectProperty() method incorrectly? Should I use some other method to create a binding of a custom object?

EDIT:

The issue was that I was trying to override the ObjectProperty<BigDecimal> from parent class with ObjectBinding<BigDecimal> . The solution, in my case, was to make the original ObjectProperty<BigDecimal> abstract, and leave implementation to the classes that inherit it.

Answer 1

All the xBinding functions returns bindings, not properties. If you think about it, how would a calculated property behave if it was writable? Should it write back into the underlying properties perhaps? TornadoFX actually supports these kinds of proxy properties as well, but I suspect that's not what you're after.

Are you wondering why you get ObjectBinding<BigDecimal?> instead of ObjectBinding<BigDecimal> ?

The reason is that the underlying property might be null, and if so we might want to return null from the calculated binding as well.

This normally doesn't create an issue, the property is still observable and would carry the correct calculated BigDecimal value.