JavaFX custom controller factory

Question

I have been experimenting with the FXMLLoader and using the setControllerFactory method using a custom Callback<P,R> implementation.

The ORACLE documentation says the following:

An implementation might return a null value to indicate that it does not or cannot create a controller of the given type; in this case, the default controller construction mechanism will be employed by the loader.

The result I want to achieve is that I can use a dependency injection framework to create any controllers that require parameters but I will let the FXMLLoader load any controllers that do not require parameters.

So if I have the following simple FXML file which uses the ViewController class which accepts no parameters...

<StackPane fx:id="pane"
          xmlns:fx="http://javafx.com/fxml"
          fx:controller="my.package.ViewController">
</StackPane>

and I use the following simple controller factory implementation to signal to the FXMLLoader that I want it to manage the construction of the controller in this case...

loader.setControllerFactory(new Callback<Class<?>, Object>(){
    @Override
    public Object Call(Class<?> type) {
        return null; // Let the FXMLLoader handle construction...
    }
});

after calling the load() method my Initialise method in the ViewController class is never called (I have verified this with a breakpoint).

If I change my controller factory implementation to return an instance of the ViewController class then everything works as expected.

Can anyone help me to clear up my confusion? Am I using the Callback interface incorrectly or is the ORACLE documentation incorrect?

Bonbon

Which version of JavaFX you are using? As the oracle's quoted description says, it may be valid for version 2.1, since the method to override is getController(Class<?> type) in there, while it is call(Class<?> param) in 2.2. So the behavior may also be changed, try with version 2.1. – Squab

I'm using version 2.2. I had noticed the difference in the callback syntax but assumed that was all that had changed since there was no mention of it in the 2.2 documentation. It's not a major problem as I can just use the dependency injection framework to create the controllers that do not have parameters in their constructors. – Bonbon

Here is FXMLLoader JavaFX 8 source code. Although it is not 2.2 but the most of their codes are similar. The only usage of controllerFactory is setController(controllerFactory.call(type));. So it maybe the same in 2.2. Just curious which DI framework are you using? – Squab

I'm planning on using Google Guice but I hadn't got that far yet as I was just evaluating the behaviour of the FXMLLoader and the controller factory callback. – Bonbon

if it is null, don't return null, instead, return type.newInstance();. – Celeski

Answer 1

javafx does the following in FXMLLoader:

    try {
      if (controllerFactory == null) {
        setController(ReflectUtil.newInstance(type));
      } else {
        setController(controllerFactory.call(type));
      }
    } catch (InstantiationException exception) {
      throw new LoadException(exception);
    } catch (IllegalAccessException exception) {
      throw new LoadException(exception);
    }

so, yes, the oracle tutorial is incorrect.

Hui

Is this from version 2.2 or from version 8 as posted in the comments by Uluk Biy? – Bonbon