JavaFX FXML

[vsquared]

The following source code demonstrates using JavaFX's FXML in py5 which works differently than it does in Processing's Java mode. Java FXML examples usually show using a 'Controller' class for event handling. However, in py5 this is not possible because setController() requires a java.lang.Object which py5 cannot deliver. To get around this limitation an alternative technique shown below has been found; so far I have not seen it described elsewhere. It works by gleaning the root control (a Pane in our case) from the output of loader.load() and then requesting a control list by using pane.getChildren(). Controls on the list are then accessible by using their list index, eg ctrl[index]. Event handling is achieved by using ctrl[x].setOnAction() to call a free-standing function which normally would be part of the Controller class, eg def btnAction(event). The 'event' parameter is important and the function will not work correctly without it. This demo uses a standard .xml file which may be edited in a text editor of your choice. A .fxml file created by the app SceneBuilder may also be used (files edited in Android Studio). Either file type will work. A controller or onAction() should not be set in either file to insure that the file will load correctly. The object of using JavaFX FXML is to isolate gui code from the main app code thereby simplifying it.

# Uses Imported mode for py5

import javafx.stage.Stage
import java.io.File
from java.io import IOException

def btnAction(event):
  print("Btn1 hit.")
  label.setText("Jeremiah was a bullfrog.")
  
def settings():
  size(1,1,FX2D)
  
def setup():
  global label
  
  stage = javafx.stage.Stage()
  loader = javafx.fxml.FXMLLoader() 
  path = str(sketch_path())
  xml = "ctrl2.xml"
  file = java.io.File(path +"/" + xml)
  uri = file.toURI()
  try:
    url = uri.toURL()
  except MalformedURLException as e:
    print("URLException:",e)
  loader.setLocation(url);
  try: 
    pane = loader.load()
  except IOException as e:
    print("IOException:",e.getCause());
  print("pane =",pane)
  ctrl = pane.getChildren()
  print("ctrl list =",ctrl)
  label = ctrl[0]
  btn = ctrl[1]
  btn.setOnAction(btnAction)
  scene = javafx.scene.Scene(pane, 300, 100)
  stage.setScene(scene)
  stage.setTitle("JavaFX FXML Demo")
  stage.show()

ctrl2.xml file (could also use .fxml)

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.Pane?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<Pane>
    <Label id="label1" layoutX="80.0" layoutY="15.0" text="Jeremiah"/>
    <Button id="btn1" layoutX="124.0" layoutY="40.0" text="Btn1"/>
</Pane>

Output:

[GoToLoop]

... requires a Java.lang.Object which py5 cannot deliver.

Have you tried class My_Controller(Java.lang.Object):?
I believe it was possible to inherit from Java's Object on Processing's Python Mode.

[vsquared]

Thanks. I'll try it.

This is what Thonny returns:

Addendum:
The following will run in Processing 3.5.4:

import java.lang.Object

class My_Controller(java.lang.Object):

  def myBtnAction():
    print("Btn hit.")
    
def setup():
  myController = My_Controller()
  print(type(myController))

returns:

But still won't load with 'onAction' in .xml file just like it did in py5. However, the method described above worked as expected.