model-view-controllerjavafximage-viewer

JavaFX: Passing on an Image extracted from a FileChooser triggered from the Root view into an ImageView object in a nested view

I'm new to JavaFX, so please forgive the noobishness.

So I'm making a Picture Viewer. This is my first time designing a GUI with the MVC paradigm, so I'm not very sure what I'm doing.

What I'm Trying To Accomplish:

It's just a normal picture viewer. Like your standard Windows program that opens when you want to look at a picture.

What I Did:

So I currently have 2 views:

  1. the Root.fxml view, which is a BorderPane with just a MenuBar on top with a MenuItem "Open" that triggers a FileChooser and sets the MainApp.java currentImage variable to whatever the user chose.

  2. Nested inside of (root.setCenter) it I have ImageViewer.fxml view, which is an AnchorPane that only contains an ImageView.

I'm 100% sure there is nothing wrong with my FXML and that all controllers and variables are bound correctly. This must be an issue in the MainApp or the Controllers.

I have no idea how to pass the Image from the RootViewController to the ImageViewerController. Whenver I try to initialize a listener for mainApp.currentImage in the ImageViewerController initializer I get a NullPointerException. If I put it in the setMainApp method it does nothing. Here's my code:

The Code:

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

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

            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());
    }
}
Solution

  • When you initialize everything, the ImageViewController is observing the imageProperty of the main app's current MyImage object. When you choose a new image from your menu, you set a new MyImage object in the main app: however the ImageViewController is still observing the imageProperty in the original MyImage object. That imageProperty never changes.

    You probably want to make currentImage final, and just change the property:

    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 final MyImage currentImage = new MyImage(img);

    public MainApp() {
    }

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

    // ...

    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);
        currentImage.setImageFile(imageFile);
        currentImage.setImage(new Image(imageFile.toURI().toString()));
    }

}

    Note you have another bug: you are calling mainApp.getCurrentImage() in the initialize() method of your controller, which is necessarily called before you get a chance to set the main app. You should register the listener in the setMainApp(...) method:

    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;


    /**
     * 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());

        mainApp.getCurrentImage().imageProperty().addListener(((observable, oldValue, newValue) -> imageView.setImage(newValue)));
    }
}