IllegalArgumentException when using FXML - tornadofx

Question

I've been following along the TornadoFX guide for using FXML (https://github.com/edvin/tornadofx/wiki/FXML), but am getting a error:
java.lang.IllegalArgumentException: FXML not found for class ui.view.BoardView
Here's my BoardView.kt view:
class BoardView : View() {
override val root: BorderPane by fxml()
val hello: Label by fxid()
init {
hello.text = "Hello World"
}
}
And here's the FXML file (in the same package, ui.view)
*
<BorderPane xmlns="http://javafx.com/javafx/null" xmlns:fx="http://javafx.com/fxml/1">
<padding>
<Insets top="20" right="20" bottom="20" left="20" />
</padding>
<center>
<HBox alignment="CENTER" spacing="10">
<Label fx:id="hello">
<font>
<Font size="20"/>
</font>
</Label>
</HBox>
</center>
</BorderPane>
Here's the full stack trace if it helps:
java.lang.IllegalArgumentException: FXML not found for class ui.view.BoardView
at tornadofx.UIComponent$fxml$1.<init>(Component.kt:360)
at tornadofx.UIComponent.fxml(Component.kt:353)
at tornadofx.UIComponent.fxml$default(Component.kt:353)
at ui.view.BoardView.<init>(BoardView.kt:12)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
at java.lang.Class.newInstance(Class.java:442)
at tornadofx.FXKt.find(FX.kt:238)
at tornadofx.App.start(App.kt:29)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$163(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$176(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$174(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$175(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
I've tried giving arguments to fxml(), from "BoardView" to "BoardView.fxml" to moving the fxml file into src/main/resources. I couldn't see anything obvious looking at the Component.kt source file.
Thanks for any help you can give me.

Answer 1

Short answer first: Put the file in src/main/resources/ui/view/BoardView.fxml and don't supply a path parameter to the fxml() call.
If you are using Maven, it will not copy fxml files in src/main/java to the target directory by default, so even if you have the fxml file in the same package it will not be available unless you instruct Maven to copy resources with .fxml extension.
I recommend that you put it in src/main/resources instead, but remember that it also has to be in the same package there, so the correct path would be src/main/resources/ui/view/BoardView.fxml.
Alternatively, if you put it directly in src/main/resources you must add this path parameter to the fxml delegate:
override val root : BorderPane by fxml("/BoardView.fxml")
Note the / prefix to make it look in the root of the classpath.
A good tip would be to compile the project and look in the output folder (target by default for Maven projects) and check that the fxml file is in the location you expect.