从线程返回图像

Question

I am basically trying to have a user input a filepath from the a FileChooser then pass that to task so it can be manipulated and turned into an image that can display in a JavaFX ImageView. My problem is that I have the task running in a thread and my method doesn't wait until the thread has finished executing to return the image needed. Is there any way of achieving this?

//JavaFX Controller with fileChooser

public class JavaCVTestController implements Initializable{

    @FXML
    ImageView image;
    @FXML
    Button btnUpload;



    FileChooser fileChooser = new FileChooser();
    String selectedFile = null;


    @Override
    public void initialize(URL location, ResourceBundle resources) {
        this.image.setPreserveRatio(true);
    }

    @FXML
    private void uploadImage(ActionEvent Event) throws IOException, Exception{



        selectedFile = fileChooser.showOpenDialog(null).getAbsolutePath();
        System.out.println(selectedFile);

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

        ProgressBarController pBarController = loader.getController();


        Stage stage = new Stage();
        stage.setScene(new Scene(root));
        stage.show();
        image.setImage(pBarController.loadImage2(selectedFile));
    }
}

//JavaFX Controller for progressbar popup

public class ProgressBarController implements Initializable{

    @FXML
    private ProgressBar pBar;
    @FXML
    private Label task;


    RandomAccessFile raf;
    TiffDecoder decoder;
    BufferedImage bufferedImage;
    Image image;


    @Override
    public void initialize(URL location, ResourceBundle resources) {

    }



    public Image loadImage2 (String filePath) throws InterruptedException, ExecutionException {
        ExecutorService service = Executors.newFixedThreadPool(1);

        Task<Image> task = new UploadTask(filePath);
        pBar.progressProperty().bind(task.progressProperty());
        this.task.textProperty().bind(task.messageProperty());
        Thread thread = new Thread(task);
        thread.start();
        return task.get();
            //NEED TO RETURN IMAGE back to previous controller somehow without interrupting the task

    }




    private class UploadTask extends Task<Image> {

        private String filePath;
        private RandomAccessFile raf;
        private TiffDecoder decoder;
        private BufferedImage bufferedImage;
        private Image image;

        public UploadTask(String filePath){
            this.filePath = filePath;
        }

        @Override
        protected Image call() throws Exception {
            updateMessage("Loading file into memory");
            generateRaf(filePath);
            updateProgress(10, 100);

            updateMessage("Decoding image format");
            decodeTiff(raf);
            updateProgress(30, 100);

            updateMessage("Buffering image to stream");
            bufferImage(decoder);
            updateProgress(600, 100);

            updateMessage("Converting to image");
            image = convertImageToFXImage(bufferedImage);
            updateProgress(90, 100);

            updateMessage("Finished");
            updateProgress(100, 100);

            return image;
        }

        private void generateRaf(String filePath) throws FileNotFoundException{
            this.raf = new RandomAccessFile(filePath, "r");
        }

        private void decodeTiff(RandomAccessFile raf) throws Exception{
            this.decoder = new TiffDecoder(raf);
        }

        private void bufferImage(TiffDecoder decoder) throws Exception{
            bufferedImage = decoder.read();
        }

        private Image convertImageToFXImage(BufferedImage bufferedImage){
            return SwingFXUtils.toFXImage(bufferedImage, null);
        }

        @Override
        protected void failed() {
            System.out.println("Upload failed");
        }

        @Override
        protected void succeeded() {
            System.out.println("Upload succeeded");
        }
    }
}

Answer 1

A fairly simple change to your code that would allow you to do this would be:

public class ProgressBarController {

    // ...

    public ReadOnlyObjectProperty<Image> loadImage2 (String filePath) throws InterruptedException, ExecutionException {
        ExecutorService service = Executors.newFixedThreadPool(1);

        Task<Image> task = new UploadTask(filePath);
        pBar.progressProperty().bind(task.progressProperty());
        this.task.textProperty().bind(task.messageProperty());
        Thread thread = new Thread(task);
        thread.start();
        return task.valueProperty();

    }

    // ...
}

and then simply

@FXML
private void uploadImage(ActionEvent Event) throws IOException, Exception{



    selectedFile = fileChooser.showOpenDialog(null).getAbsolutePath();
    System.out.println(selectedFile);

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

    ProgressBarController pBarController = loader.getController();


    Stage stage = new Stage();
    stage.setScene(new Scene(root));
    stage.show();
    image.imageProperty().bind(pBarController.loadImage2(selectedFile));
}

But I think you probably want to refactor this, so that it properly separates concerns (single responsibility principle). Essentially, your problem arises because you don't have access to the task at the point where you have access to the image view; this is because the task is (incorrectly) encapsualted by the progress bar controller. Your progress bar controller shouldn't really be responsible for loading the image (again: single responsibility principle); you can just let it expose the progress property from the progress bar. Something like:

public class ProgressBarController {

    @FXML
    private ProgressBar pBar;
    @FXML
    private Label task;

    public DoubleProperty progressProperty() {
        return pBar.progressProperty();
    }

    public StringProperty textProperty() {
        return task.textProperty();
    }

}

Promote the UploadTask to a standalone class:

public class UploadTask extends Task<Image> {

    private File file ;
    private BufferedImage bufferedImage ;

    public UploadTask(File file){
        this.file = file;
    }

    @Override
    protected Image call() throws Exception {
        updateMessage("Loading file into memory");
        RandomAccessFile raf = generateRaf(file);
        updateProgress(10, 100);

        updateMessage("Decoding image format");
        TiffDecoder decoder = decodeTiff(raf);
        updateProgress(30, 100);

        updateMessage("Buffering image to stream");
        BufferedImage bufferedImage = bufferImage(decoder);
        updateProgress(600, 100);

        updateMessage("Converting to image");
        Image image = convertImageToFXImage(bufferedImage);
        updateProgress(90, 100);

        updateMessage("Finished");
        updateProgress(100, 100);

        return image;
    }

    private RandomAccessFile generateRaf(File file) throws FileNotFoundException{
        return new RandomAccessFile(file, "r");
    }

    private TiffDecoder decodeTiff(RandomAccessFile raf) throws Exception{
        return new TiffDecoder(raf);
    }

    private BufferedImage bufferImage(TiffDecoder decoder) throws Exception{
       return decoder.read();
    }

    private Image convertImageToFXImage(BufferedImage bufferedImage){
        return SwingFXUtils.toFXImage(bufferedImage, null);
    }

    @Override
    protected void failed() {
        System.out.println("Upload failed");
    }

    @Override
    protected void succeeded() {
        System.out.println("Upload succeeded");
    }
}

And now do

public class JavaCVTestController {

    @FXML
    private ImageView image;
    @FXML
    private Button btnUpload;

    private ExecutorService exec = Executors.newCachedThreadPool();

    private FileChooser fileChooser = new FileChooser();


    // can't you do this in the FXML?
    public void initialize(URL location, ResourceBundle resources) {
        this.image.setPreserveRatio(true);
    }

    @FXML
    private void uploadImage(ActionEvent Event) throws IOException, Exception{



        File selectedFile = fileChooser.showOpenDialog(image.getScene().getWindow());

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

        ProgressBarController pBarController = loader.getController();

        Task<Image> uploadTask = new UploadTask(selectedFile);
        pBarController.progressProperty().bind(uploadTask.progressProperty());
        pBarController.textProperty().bind(uploadTask.messageProperty());

        uploadTask.setOnSucceeded(e -> image.setImage(uploadTask.getValue()));

        Stage stage = new Stage();
        stage.setScene(new Scene(root));
        stage.show();

        exec.execute(uploadTask);
    }
}

Note that I cleaned up various aspects of the code for common-or-garden best practice.