Have a MenuItem trigger a Filechooser to choose an Image to put in an ImageViewer

[John Jeffersonian]

Hello,

I want to have a MenuItem trigger a Filechooser to choose an Image to put in an ImageViewer, but for some reason the ImageViewer parent view (which is seperate from the root view and is inside the root view) controller initializer keeps throwing a NullPointerException on a addListener statement that I want to use for the ImageViewer to change the Image automatically when the currentImage changes (i.e. when the user chooses a new Image through the MenuItem). It's driving me mad, I'm new to JavaFX, so please be gentle to my stupidity. I won't post my FXMLs as I'm 100% adamant I've binded everything inside SceneBuilder correctly.

Below is my source code, in ImageViewerController.java I've commented to the right of the line that throws the NullPointerException.

MainApp.java

import sample.model.MyImage;
import samlple.view.ImageViewerController;
import sample.view.RootController;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.stage.FileChooser;
import javafx.stage.Stage;

import java.io.File;
import java.io.IOException;

public class MainApp extends Application {
    final static File img = new File("C:\\test\\1.png"); // test initial image loading
    private Stage primaryStage;
    private BorderPane rootLayout;
    private MyImage currentImage = new MyImage(img);

    public MainApp() {
    }

    public MyImage getCurrentImage(){
        return this.currentImage;
    }
    public void setCurrentImage(MyImage myImage){
        currentImage = myImage;
    }

    public void start(Stage primaryStage) throws Exception{
        this.primaryStage = primaryStage;
        this.primaryStage.setTitle("Hi");

        initRootLayout();
        showImageViewer();
    }



    /**
     * Initializes the root layout.
     */
    public void initRootLayout() {
        try {
            // Load root layout from fxml file.
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainApp.class.getResource("view/Root.fxml"));
            rootLayout = loader.load();

            // Giving the controller access to the main app.
            RootController controller = loader.getController();
            controller.setMainApp(this);

            // Show the scene containing the root layout.
            Scene scene = new Scene(rootLayout);
            primaryStage.setScene(scene);
            primaryStage.show();

        } catch (IOException e) {
            e.printStackTrace();
            System.err.println("Root layout loading error.");
        }
    }

    /**
     * Shows the ImageViewer inside the root layout.
     */
    public void showImageViewer() {
        try {
            // Load ImageViewer.
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainApp.class.getResource("view/ImageViewer.fxml"));
            AnchorPane imageViewer = loader.load();

            // Set the ImageViewer into the center of root layout.
            rootLayout.setCenter(imageViewer);

            // Giving the controller access to the main app.
            ImageViewerController controller = loader.getController();
            controller.setMainApp(this);

        } catch (IOException e) {
            e.printStackTrace();
            System.err.println("ImageViewer layout loading error.");
        }
    }

    /**
     *  Called when user clicks the "Open" menu item
     */

    public void menuOpenImageFile() {
        FileChooser fileChooser = new FileChooser();

        //Set extension filter
        FileChooser.ExtensionFilter extFilter = new FileChooser.ExtensionFilter("Image types (*.jpg;  *.gif; *.bmp; *.png)", "*.jpg", "*.png", "*.bmp", "*.gif");
        fileChooser.getExtensionFilters().add(extFilter);

        //Show save file dialog
        File imageFile = fileChooser.showOpenDialog(primaryStage);
        MyImage myImageToSetAsCurrent = new MyImage(imageFile);
        setCurrentImage(myImageToSetAsCurrent);
    }

    /**
     * Returns the main stage.
     * @return
     */
    public Stage getPrimaryStage() {
        return primaryStage;
    }

    public static void main(String[] args) { launch(args); }
}

MyImage.java (a model image class to hold properties):

package sample.model;


import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.scene.image.Image;

import java.io.File;

public class MyImage {
    private final ObjectProperty<File> imageFile;
    private final ObjectProperty<Image> image;

    public MyImage(){
        this(null);
    }

    public MyImage(File imageFile) {
        this.imageFile = new SimpleObjectProperty<>(imageFile);
        this.image = new SimpleObjectProperty<>(new Image("file:" + imageFile.toString()));
    }

    public File getImageFile() {
        return imageFile.get();
    }

    public ObjectProperty<File> imageFileProperty() {
        return imageFile;
    }

    public void setImageFile(File myImageFile) {
        this.imageFile.set(myImageFile);
    }

    public Image getImage() {
        return image.get();
    }

    public ObjectProperty<Image> imageProperty() {
        return image;
    }

    public void setImage(Image myImage) {
        this.image.set(myImage);
    }
}

RootController.java

import samlple.MainApp;
import javafx.fxml.FXML;
import javafx.scene.control.MenuItem;


public class RootController {
    @FXML
    private MenuItem open;

    // Reference to the main application.
    private MainApp mainApp;

    /**
     * The constructor.
     * The constructor is called before the initialize() method.
     */
    public RootController() {
    }

    /**
     * Initializes the controller class. This method is automatically called
     * after the fxml file has been loaded.
     */
    @FXML
    private void initialize() {
    }

    @FXML
    private void openImageFile () {
        mainApp.menuOpenImageFile();
    }

    /**
     * Is called by the main application to give a reference back to itself.
     *
     */
    public void setMainApp(MainApp mainApp) {
        this.mainApp = mainApp;

    }
}

ImageViewerController.java

import sample.MainApp;
import javafx.fxml.FXML;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;


public class ImageViewerController {
    @FXML
    private ImageView imageView;

    // Reference to the main application.
    private MainApp mainApp;

    /**
     * The constructor.
     * The constructor is called before the initialize() method.
     */
    public ImageViewerController() {
    }

    /**
     * Initializes the controller class. This method is automatically called
     * after the fxml file has been loaded.
     */
    @FXML
    private void initialize() {
        mainApp.getCurrentImage().imageProperty().addListener(((observable, oldValue, newValue) -> imageView.setImage(newValue))); //This keeps throwing NullPointerException!
    }

    /**
     * Is called by the main application to give a reference back to itself.
     *
     */
    public void setMainApp(MainApp mainApp) {
        this.mainApp = mainApp;

        imageView.setImage(mainApp.getCurrentImage().imageProperty().get());
    }
}

Error Messages:

javafx.fxml.LoadException: 
/C:/sample/view/ImageViewer.fxml

	at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
	at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2571)
	at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
	at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2409)
	at sample.MainApp.showImageViewer(MainApp.java:76)
	at sample.MainApp.start(MainApp.java:38)
	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)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
	at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
	at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2566)
	... 13 more
Caused by: java.lang.NullPointerException
	at sample.view.ImageViewerController.initialize(ImageViewerController.java:29)
	... 23 more
ImageViewer layout loading error.