JavaFXML loader cannot properly load my controller class, because the required variables compile to names like

private javafx.scene.control.TextField ui$FXMLAttrEditorController$$intField;
private javafx.scene.control.TextField ui$FXMLAttrEditorController$$xField;
private javafx.scene.control.TextField ui$FXMLAttrEditorController$$yField;
.
The correct names would be

private javafx.scene.control.TextField intField;
private javafx.scene.control.TextField xField;
private javafx.scene.control.TextField yField;

(as reported by javap.exe).

See attached file. It is extracted from a working project, but should compile alone, if you remove the "irrelevant" parameter. The problem gets triggered around line 40.

If you need build.sbt, try this:

scalaVersion := "2.11.4"

libraryDependencies ++= Seq(
"org.scalafx" %% "scalafx" % "8.0.20-R6",
)