Strange type mismatch error

Question

I have a table column errorFixed of type TableColumn[Error, Boolean] inside a TableView[Error]. My Error class has a val fixed: Boolean which I try to put into this table column.

I tried

errorFixed.cellValueFactory = features => 
  ReadOnlyBooleanWrapper(features.value.fixed)

but it fails with

type mismatch;
found   : scalafx.beans.property.ReadOnlyBooleanWrapper
required: scalafx.beans.value.ObservableValue[Boolean,Boolean]

which I really don't understand as ObservableValue[Boolean,Boolean] is a supertype of ReadOnlyBooleanWrapper according to the documentation.

If I cast it myself using .asInstanceOf[ObservableValue[Boolean, Boolean]] it seems to work. What is going on here?

Gist with stripped down project to reproduce

Answer 1

Short answer is: instead of

errorFixed.cellValueFactory = features => 
  ReadOnlyBooleanWrapper(features.value.fixed)

you should use

errorFixed.cellValueFactory = features => 
  ObjectProperty[Boolean](features.value.fixed)

or ReadOnlyObjectWrapper[Boolean].

A brief version of long answer: there are certain "frictions" between Scala and Java when working with primitive Java types, like boolean or int. This inconvenience shows up in property binding in ScalaFX. Not everything is inherited in an intuitive way. In this case

ReadOnlyBooleanWrapper 

is a subclass of

ObservableValue[scala.Boolean, java.lang.Boolean]

but scala.Boolean is not a subclass of java.lang.Boolean which internally, in ScalaFX this leads to complications. Interesting thing is that the casting .asInstanceOf[ObservableValue[scala.Boolean, scala.Boolean]] works, though type parameters do not match at compile time.

Thanks for positing a full code example (gist) this really helps in clarifying the question.