[FIXED] Interact between several FXMLs

Issue

I'm trying to write my first application with javaFX and FXML files, but I got stuck with accesing variables of the FXMLs.

I am able to start the program with the first scene (first FXML). There is a button I'm able to interact with, and the first scene hides and the second scene appears. In that scene, the user has to insert a value in a text field. I'm able to save this into a variable by confirming this input over another button. This button click hides the second scene and opens the first scene again. Now I want to set the value of a label in that first scene to the value of the variable I saved the user's input in. But this throws an error message. It seems like this label value is not accessable, even if this label is part of the currently loaded FXML, but I am able to get the value of a label of the second FXML (user interaction field), which isn't visible anymore.

Can anyone help me, how to make this Label of the first FXML readable and changable? My code is quite long, but I tired to give you the most important parts:

@FXML
private Label RollsMax;
@FXML
private TextField roll_input;
@FXML
private String amountRolls;
... // several more declarations
@FXML
void btn_confirmInput_onClick(ActionEvent event){ //btn_confirmInput is part of scene2.fxml
   event.consume();
   amountRolls=roll_input.getText();
   System.out.println(amountRolls); // here I get the result of the user's input
   try{
      root=FXMLLoader.load(getClass().getResource("project/scene1.fxml"));
      stage=(Stage)((Node)event.getSource()).getScene().getWindow();
      scene=new Scene(root);
      stage.setScene(scene);
      stage.show();
   } //end try
   catch (IOException e){
      e.printStackTrace();
   } //end catch
   RollsMax.setText(amountRolls); // THIS LINE IS NOT WORKING AS RollsMax SEEMS NOT AVAILABLE, EVEN IF IT IS PART OF SCENE1.fxml
} // end btn_confirmInput_onClick()

Any ideas? The error I get is 'java.lang.RuntimeException: java.lang.reflect.InvocationtargetException' as well as a'java.lang.NullPointerException'.

Thanks a lot! Endcoder

Solution

To share data between the scenes, we'll introduce a Model class that holds the shared information:

public class Model {

    private SimpleStringProperty valueProperty = new SimpleStringProperty("N/A");

    public SimpleStringProperty getValueProperty() {
        return valueProperty;
    }
}

And an interface to be implemented by the controllers of the two scenes (actually the controllers of the two roots of the two scenes).
The interface adds the functionality of injection a Model into the controller:

public interface Controller {
    void setModel(Model model);
} 

sceneOne.fxml with a button to switch scene and a label to display user's input:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" 
 prefHeight="300.0" prefWidth="400.0" xmlns="http://javafx.com/javafx/16" 
 xmlns:fx="http://javafx.com/fxml/1" fx:controller="SceneOneController">
   <children>
      <Label layoutX="159.0" layoutY="40.0" text="Scene 1">
         <font>
            <Font size="24.0" />
         </font>
      </Label>
      <Button layoutX="264.0" layoutY="246.0" mnemonicParsing="false" onAction="#changeScene" prefHeight="26.0" prefWidth="102.0" text="Get Input" />
      <Label fx:id="inputValue" layoutX="187.0" layoutY="142.0" text="Label" />
   </children>
</AnchorPane>

And its controller which implements the Controller interface:

public class SceneOneController implements Controller {

    @FXML Label inputValue;
    private Model model;

    public void changeScene(ActionEvent e) {
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource("sceneTwo.fxml"));
            Parent root = loader.load();
            Controller controller = loader.getController(); //get a reference to sceneTwo controller
            controller.setModel(model);
             Stage stage = (Stage)((Node)e.getSource()).getScene().getWindow();
             stage.setScene(new Scene(root));
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    @Override
    public void setModel(Model model) {
        this.model = model;
        if(model != null){
            inputValue.textProperty().unbind();
            inputValue.textProperty().bind(model.valueProperty);
        }
    }
}

sceneTwo.fxml with a button to switch scene and a TextField for the user's input:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane fx:id="main" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="300.0" prefWidth="400.0" xmlns="http://javafx.com/javafx/16" xmlns:fx="http://javafx.com/fxml/1" fx:controller="SceneTwoController">
   <children>
      <Label layoutX="150.0" layoutY="41.0" text="Scene 2">
         <font>
            <Font size="24.0" />
         </font>
      </Label>
      <Button layoutX="264.0" layoutY="246.0" mnemonicParsing="false" onAction="#changeScene" prefHeight="26.0" prefWidth="102.0" text="Update" />
      <TextField fx:id="inputValue" layoutX="121.0" layoutY="138.0" prefHeight="25.0" prefWidth="162.0" />
   </children>
</AnchorPane>

And its controller:

public class SceneTwoController implements Controller {

    @FXML TextField inputValue;
    private Model model;

    public void changeScene(ActionEvent e) {
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource("sceneOne.fxml"));
            Parent root = loader.load();
            Controller controller = loader.getController();  //get a reference to sceneOne controller
            controller.setModel(model);
             Stage stage = (Stage)((Node)e.getSource()).getScene().getWindow();
             stage.setScene(new Scene(root));
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    @Override
    public void setModel(Model model) {
        this.model = model;
        if(model != null){
            inputValue.textProperty().unbind();
            model.valueProperty.bind(inputValue.textProperty());
        }
    }
}

And finally the application to test it all:

public class SwitchSceneMVC extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{

        FXMLLoader loader = new FXMLLoader(getClass().getResource("sceneOne.fxml"));
        Parent root = loader.load();

        Model model = new Model();
        Controller controller = loader.getController();
        controller.setModel(model);

        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }
    public static void main(String[] args) {
        launch(null);
    }
}

Answered By - c0der
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)