MyPhotoViewer.java

package com.test.main;

import java.io.File;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.geometry.Pos;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ProgressIndicator;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.input.DragEvent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.FlowPane;
import javafx.stage.Stage;

public class MyPhotoViewer extends Application{

    private ArrayList<String> imgFiles = new ArrayList<String>();
    private ImageView imgViewer;
    private int currentImage;
    private Task loadImage;
    private ProgressIndicator loadingPie;

    @Override
    public void start(Stage stage) {
        try {
            Group root = new Group();
            Scene scene = new Scene(root, 480, 400);
            loadingPie = new ProgressIndicator(0);

            this.enableDragSupport(scene);

            BorderPane bp = new BorderPane();

            File fileImg = new File("C:\\Users\\User\\Pictures\\test1.jpg"); // Initial image

            Image myImg = new Image(fileImg.toURI().toURL().toString());
            currentImage = 0;
            imgViewer = new ImageView(myImg);
            imgViewer.setFitHeight(580);
            imgViewer.setFitWidth(470);
            imgViewer.setPreserveRatio(true);

            Button btnPrev = new Button("<");
            Button btnNext = new Button(">");
            this.applyHandler(btnPrev);
            this.applyHandler(btnNext);

            FlowPane buttons = new FlowPane();
            buttons.setAlignment(Pos.CENTER);
            buttons.getChildren().addAll(btnPrev, btnNext);

            loadingPie.setVisible(false);
            //this.loadImgManual(); // in case drag n drop does not work.
            bp.setTop(loadingPie);
            bp.setCenter(imgViewer);
            bp.setBottom(buttons);

            root.getChildren().add(bp);

            stage.setScene(scene);
            stage.show();
        } catch (MalformedURLException ex) {
            Logger.getLogger(MyPhotoViewer.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

    private void applyHandler(Button prmBtn){
        prmBtn.setOnAction((t) -> {
           switch(prmBtn.getText()){
               case ">":
                   System.out.println(">");
                   loadingPie.setVisible(true);
                   loadImage = loadImgTask(prmBtn.getText());
                   loadingPie.progressProperty().unbind();
                   loadingPie.progressProperty().bind(loadImage.progressProperty());
                   new Thread(loadImage).start();
                   break;
               case "<":
                   System.out.println("<");
                   loadImage = loadImgTask(prmBtn.getText());
                   loadingPie.setVisible(true);
                   loadImage = loadImgTask(prmBtn.getText());
                   loadingPie.progressProperty().unbind();
                   loadingPie.progressProperty().bind(loadImage.progressProperty());
                   new Thread(loadImage).start();
                   break;
               default:
                   System.err.println("Cannot process that.");
           }
        });
    }

    private Task loadImgTask(String prmCommand){
    return new Task() {
        @Override
        protected Object call() throws Exception {
            showImage(prmCommand);
            loadingPie.setVisible(false);

            return true;
        }
    };
    }

    private void loadImgManual(){

        try {
            imgFiles.add(new File("C:\\Users\\User\\Pictures\\test1.jpg").toURI().toURL().toString());
            imgFiles.add(new File("‪C:\\Users\\User\\Pictures\\test2.jpg").toURI().toURL().toString());
            imgFiles.add(new File("C:\\Users\\User\\Pictures\\test3.jpg").toURI().toURL().toString());
            imgFiles.add(new File("C:\\Users\\User\\Pictures\\test4.jpg").toURI().toURL().toString());
            imgFiles.add(new File("C:\\Users\\User\\Pictures\\test5.jpg").toURI().toURL().toString());
        } catch (MalformedURLException ex) {
            Logger.getLogger(MyPhotoViewer.class.getName()).log(Level.SEVERE, null, ex);
        }

    }


    private void enableDragSupport(Scene prmScene){ // does not work

        prmScene.setOnDragOver((DragEvent event) -> {
            System.out.println("Drop detected");
            Dragboard db = event.getDragboard();
            if (db.hasFiles() || (db.hasUrl())) {
                event.acceptTransferModes(TransferMode.LINK);
            } else {
                event.consume();
            }
        });

        prmScene.setOnDragDropped((DragEvent event) -> {
            Dragboard db = event.getDragboard();
            System.out.println("Drop detected");
            if(db.hasFiles()){
                db.getFiles().stream().forEach(file -> {
                    try {
                        imgFiles.add(file.toURI().toURL().toString());
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                });
            }
            event.setDropCompleted(true);
            event.consume();
        });
    }

    private void showImage(String prmCommand){ // works but blanks the whole scene.
        switch(prmCommand){
            case ">":
                if (currentImage+1 <= imgFiles.size()) {
                    currentImage += 1;
                    imgViewer.setImage(new Image(imgFiles.get(currentImage)));
                }else{
                    System.err.println("End reached: No more images to load.");
                }
                break;

            case "<":
                if (currentImage-1 >= 0) {
                    currentImage -= 1;
                    imgViewer.setImage(new Image(imgFiles.get(currentImage)));
                }else{
                    System.err.println("End reached: No more images to load.");
                }
                break;
            default:
                System.err.println("Cannot load that!");
                break;
        }

    }

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



}