Passing ObservableList from one class to another

Question

Hi there I am trying to pass an ObservableList from one class to another but seem to be getting an error

java.lang.NullPointerException

java.lang.NullPointerException
 at animal_sanctuary.maintenanceController.populateBreedTable(maintenanceController.java:99)
 at animal_sanctuary.maintenanceController.initialize(maintenanceController.java:44)
 at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
 at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
 at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2409)
 at animal_sanctuary.Controller.loadScreen(Controller.java:133)
 at animal_sanctuary.Main.start(Main.java:33)
 at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$163(LauncherImpl.java:863)
 at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$176(PlatformImpl.java:326)
 at com.sun.javafx.application.PlatformImpl.lambda$null$174(PlatformImpl.java:295)
 at java.security.AccessController.doPrivileged(Native Method)
 at com.sun.javafx.application.PlatformImpl.lambda$runLater$175(PlatformImpl.java:294)
 at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
 at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
 at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
 at java.lang.Thread.run(Thread.java:745)

Can you tell me what i am doing wrong its is driving me crazy .

Here is my Code

Class 1

//===================================================
    //      ***** GET INFO FROM DB *****
    //===================================================
    
    public ObservableList<Breed> getBreed(){

        Statement stmt = null;

        ArrayList<Breed> bre = new ArrayList<Breed>();
        try {
            stmt = conn.createStatement();
            ResultSet rs;
            rs = stmt.executeQuery("SELECT * FROM breeds;");
            while(rs.next()){
                String s = rs.getString("breed");
                System.out.println(s);
                Breed b = new Breed(s);
                bre.add(b);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        ObservableList<Breed> myObservableList = FXCollections.observableArrayList(bre);;

        return myObservableList;
    }

Class 2

public void populateBreedTable(){

        ObservableList<Breed> b = myController.getBreed();
        //breedCol.setCellValueFactory(new PropertyValueFactory<>("breed"));
        //itemTable.setItems();

    }

Thanks you for your time :)

**UPDATE

public class maintenanceController implements Initializable, ControlledScreen {

Controller myController;
Connection conn;

@FXML
RadioButton rbType ,rbBreed, rbLocation;
@FXML
TextField addItemTb;
@FXML
TableView<Breed>  itemTable;
@FXML
TableColumn<Breed, String > breedCol;
@FXML
TableView<Type>  itemTable1;
@FXML
TableColumn<Type, String > TypeCol;


/**
 * Initializes the controller class.
 */
@Override
public void initialize(URL url, ResourceBundle rb) {
    // TODO
    try {
        conn = myController.getConnection();
        populateBreedTable();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

public void setScreenParent(Controller screenParent) {
    myController = screenParent;
}

@FXML
private void goToMainScreen(ActionEvent event) {
    myController.setScreen(Main.mainScreen1ID);
}

**

public boolean setScreen(final String name) { if (screens.get(name) != null) { //screen loaded final DoubleProperty opacity = opacityProperty();

        if (!getChildren().isEmpty()) {    //if there is more than one screen
            Timeline fade = new Timeline(
                    new KeyFrame(Duration.ZERO, new KeyValue(opacity, 1.0)),
                    new KeyFrame(new Duration(1000), new EventHandler<ActionEvent>() {
                        @Override
                        public void handle(ActionEvent t) {
                            getChildren().remove(0);                    //remove the displayed screen
                            getChildren().add(0, screens.get(name));     //add the screen
                            Timeline fadeIn = new Timeline(
                                    new KeyFrame(Duration.ZERO, new KeyValue(opacity, 0.0)),
                                    new KeyFrame(new Duration(800), new KeyValue(opacity, 1.0)));
                            fadeIn.play();
                        }
                    }, new KeyValue(opacity, 0.0)));
            fade.play();

        } else {
            setOpacity(0.0);
            getChildren().add(screens.get(name));       //no one else been displayed, then just show
            Timeline fadeIn = new Timeline(
                    new KeyFrame(Duration.ZERO, new KeyValue(opacity, 0.0)),
                    new KeyFrame(new Duration(2500), new KeyValue(opacity, 1.0)));
            fadeIn.play();
        }
        return true;
    } else {
        System.out.println("screen hasn't been loaded!!! \n");
        return false;
    }
}

It seems to my like you never instantiated ```myController``` — Jorn Vernee, May 07 '16 at 18:31
And by the way, those snippet things don't work with java. You should just use regular code blocks. — Jorn Vernee, May 07 '16 at 18:32
@JornVernee I have been using the controller in other method tho — Amy Hyland, May 07 '16 at 18:34
It looks like `myController` is null. Note that in the default use of JavaFX, the controller is instantiated from the `FXMLLoader` and you retrieve it from the loader (so you should not instantiate it yourself, as per the other comments). — James_D, May 07 '16 at 18:34
Be careful you don't close your connection and your statement which can cause a connection leak — Nicolas Filotto, May 07 '16 at 18:34
@James_D it is a controler parent to my fmxl contoller to pass data between controller when i change screens — Amy Hyland, May 07 '16 at 18:53
Well, assuming that line is the line throwing the exception (which is the only possibility in the code you have shown), `myController` is null. Show where you initialize it. — James_D, May 07 '16 at 18:55
OK. There is nowhere in that code where you initialize `myController`. — James_D, May 07 '16 at 19:09
@James_D yes there is public void setScreenParent(Controller screenParent) { myController = screenParent; } — Amy Hyland, May 07 '16 at 19:25
@James_D this works fine for all my other classes . This how it is done following the oracle tutorials — Amy Hyland, May 07 '16 at 19:26
Ah, OK, didn't see that. But where is it called from? You should create (probably from scratch, given the complexity of this application) a [MCVE] and post it in the question. It's pretty much impossible to diagnose the problem without enough code to reproduce it. — James_D, May 07 '16 at 19:28
@James_D Ya okay your probably write I got it working by calling the sql in class itself but i was not what I was planing. But anyway think for your help sir. Much appreciated — Amy Hyland, May 07 '16 at 19:35

score 1 · Accepted Answer · answered May 07 '16 at 19:40

The problem arises from the order in which the methods are executed. initialize() is called by the FXMLLoader as part of the process of loading the fxml file. Since your initialize() method invokes populateBreedTable(), the populateBreedTable() method is invoked before the call to FXMLLoader.load() completes.

The myController variable is only initialized by a call to setScreenParent() which almost certainly happens after you call load() on the FXMLLoader (typically you call load and then get a reference to the controller the loader created). Thus populateBreedTable() is called before myController is initialized, and is null. You can move the call to populateBreedTable() to setScreenParent() and it should work.

Passing ObservableList from one class to another

1 Answers1