Javafx pass parameter and values from one controller to another - javafx

Question

I am new to JavaFx and hence I cannot find a solution to solve my problem
Suppose I have following application structure :
- views
- first.fxml -> this has a button called btnSend and a textfield called txtEnter
- second.fxml -> this has a textarea called txtView
- Controller
- FirstController -> controller for First
- SecondController -> controller for second
- Modal
- AppModal -> here I have a getter and a setter method ,
as getText() and setText(String text)
- App
- Main.java -> This one used FXMLLoader to load first.fxml and second.fxml together.
What is the optimal/best way to display the text in SecondController passing it from FirstController. I mean, I enter a text in txtEnter and press the button btnSend and after pressing the button I want the text to be displayed in txtView which is using another controller.
I have read a lot about the observers pattern and JavaFX properties can be used to solve this, but unfortunately I am unable to implement a working solution.
I would be humbly thankful if you experts can help me in this. I know its not correct but can anyone please give me a working solution for the above project structure.
Thanks in advance.

Answer 1

Use an observable StringProperty in the model:
public class AppModel {
private final StringProperty text = new SimpleStringProperty();
public StringProperty textProperty() {
return text ;
}
public final String getText() {
return textProperty().get();
}
public final void setText(String text) {
textProperty().set(text);
}
}
Make your controllers have access to the model:
public class FirstController {
private final AppModel model ;
#FXML
private TextField textEnter ;
public FirstController(AppModel model) {
this.model = model ;
}
// action event handler for button:
#FXML
private void sendText() {
model.setText(textEnter.getText());
}
}
and
public class SecondController {
private final AppModel model ;
#FXML
private TextArea txtView ;
public SecondController(AppModel model) {
this.model = model ;
}
public void initialize() {
// update text area if text in model changes:
model.textProperty().addListener((obs, oldText, newText) ->
txtView.setText(newText));
}
}
The slightly tricky part now is that the controllers don't have a no-arg constructor, which means the default mechanism for the FXMLLoader to create them won't work. The easiest way is to set them manually. Remove both the <fx:controller> attributes from the FXML files, and then in your Main class do
AppModel model = new AppModel();
FXMLLoader firstLoader = new FXMLLoader(getClass().getResource("first.fxml"));
firstLoader.setController(new FirstController(model));
Parent firstUI = firstLoader.load();
FXMLLoader secondLoader = new FXMLLoader(getClass().getResource("second.fxml"));
secondLoader.setController(new SecondController(model));
Parent secondUI = secondLoader.load();
If you prefer to keep the <fx:controller> attributes in the FXML files, you can use a controllerFactory instead, which essentially instructs the FXMLLoader as to how to create a controller:
AppModel model = new AppModel();
Callback<Class<?>, Object> controllerFactory = type -> {
if (type == FirstController.class) {
return new FirstController(model);
} else if (type == SecondController.class) {
return new SecondController(model);
} else {
try {
return type.newInstance() ; // default behavior - invoke no-arg construtor
} catch (Exception exc) {
System.err.println("Could not create controller for "+type.getName());
throw new RuntimeException(exc);
}
}
};
FXMLLoader firstLoader = new FXMLLoader(getClass().getResource("first.fxml"));
firstLoader.setControllerFactory(controllerFactory);
Parent firstUI = firstLoader.load();
FXMLLoader secondLoader = new FXMLLoader(getClass().getResource("second.fxml"));
secondLoader.setControllerFactory(controllerFactory);
Parent secondUI = secondLoader.load();
You can make the controller factory even more flexible by using (more) reflection; basically you can implement the logic "if the controller type has a constructor taking an AppModel, call that constructor, otherwise call the no-arg constructor".
If you are creating a large application which needs to do a lot of this, then you might consider using afterburner.fx, which is a framework that essentially allows you to inject the model into the controllers using annotations.