Casting Object Type

[vsquared]

I have a custom class which is a py5.object:
<py5.BtnOneController object at 0x13c3ea2f0>
I need to pass that class to a javafx.fxml function which requires a 'java.lang.Object'
public void javafx.fxml.FXMLLoader.setController(java.lang.Object)
Is there a way to cast from a py5.object to a java.lang.Object?
I tried casting it like this, but Thonny returns an error:

[hx2A]

Can we see more of the code?

I don't know what py5.BtnOneController is. That is not a part of py5.

jpype should handle object conversion. if the btnOneController variable is a Java object, you shouldn't need to do a cast of any kind. loader.setController(btnOneController) should work.

[hx2A]

I found the JavaFX Java Docs and I see setController() does expect a parameter of type Object:

https://docs.oracle.com/javase/8/javafx/api/javafx/fxml/FXMLLoader.html#setController-java.lang.Object-

Interesting. I don't think I know enough about JavaFX to help here. Why does it accept type Object? What does it do with the object you pass?

You should still be able to use jpype's JProxy functionality here though. It's a bit of a hack, but if your class implements any Java Interface at all and has JProxy setup correctly, you'd be able to pass it to that method.

[vsquared]

Why does it accept type Object? What does it do with the object you pass? Reference is below; look under setController()
https://download.java.net/java/early_access/javafx23/docs/api/javafx.fxml/javafx/fxml/FXMLLoader.html

[hx2A]

Sets the controller associated with the root object. The value passed to this method is used as the value of the fx:controller attribute. This method must be called prior to loading the document when using controller event handlers when an fx:controller attribute is not specified in the document.

That means nothing to me. I don't know enough about JavaFX to understand this.

[vsquared]

fx:controller is automatically added to the root object (a Pane in our case) in a .fxml file, when set in SceneBuilder (which is similar to XCode). This is an alternative to setting the controller manually in code which I'm trying to do. There is still another technique which is to use a script inside of the .fxml file to do simple event handling but just about everybody agrees this is not reliable. I've tried all of these things and haven't gotten any of them to work in py5 and there is next to no help on the internet. I'm just about ready to give up, but will keep trying for a little while longer. I've also read the JProxy reference and that's Greek to me. Is there a demo somewhere?

[hx2A]

I'm just about ready to give up, but will keep trying for a little while longer. I've also read the JProxy reference and that's Greek to me. Is there a demo somewhere?

Ooops, I made a mistake, I should have directed you to JImplement, not JProxy. It looks like they are the same basic thing but the documentation says to use JImplement. Also, that's what py5 uses. Still, no part of this made any sense to me the first few times I used it.

A concrete example would help. Here is the Java interface Py5Bridge:

py5generator/py5_jar/src/main/java/py5/core/Py5Bridge.java

Line 22 in 3482ed7

public interface Py5Bridge {

That is implemented in Python by the class Py5Bridge. Observe the decorators JImplement and JOverride.

py5generator/py5_resources/py5_module/py5/bridge.py

Line 185 in 3482ed7

@JImplements("py5.core.Py5Bridge")

Instances of the Python Py5Bridge class can be passed to Java. The object gets created in Python and passed to Java here:

py5generator/py5_resources/py5_module/py5/sketch.py

Line 316 in 3482ed7

self._instance.buildPy5Bridge(

The Java method that receives it is here:

py5generator/py5_jar/src/main/java/py5/core/SketchBase.java

Line 79 in 3482ed7

public void buildPy5Bridge(Py5Bridge py5Bridge, boolean inIPythonSession, boolean inJupyterZMQShell) {

For your situation, and I have no idea if this will work or will cause other problems, is to implement a dummy Java Interface that does nothing, then use JImplements to say that it implements that Interface. Any interface should also be a java.lang.Object instance. So you might be able to pass that those Python objects here.

I still don't understand the JavaFX stuff and what this has to do with XML. Is there some kind of GUI design tool that you use to build a screen that saves configuration information as XML? If so, I've never used that. I suspect that the "root" object should be something GUI related, but I don't know, I've never done this before.

[vsquared]

Is there some kind of GUI design tool that you use to build a screen that saves configuration information as XML? Yes, it's called SceneBuilder: https://gluonhq.com/products/scene-builder/ It creates an .fxml file which you can open in Android Studio; you can also roll your own .xml file in a regular text editor if you know xml syntax or copy/paste .fxml code from SceneBuilder and modify it to suit your needs (and change the extension to .xml from. fxml). Basically the technique gets all the gui code out of your main app. Some users don't like the programmatic approach and would rather drag 'n drop controls. However, it usually takes longer to hook everything up until you figure out how the IDE works. In our case we still don't know how to add the event handlers; everything was written for Java initially, not Python.

[hx2A]

I see. Getting that to work well with py5 might require doing some Java programming to facilitate the event handlers. I'm not sure how to do that though because I am not familiar with that part of the Java world.