JavaFX - 如何控制和显示进度事件

import javafx.application.Application;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ProgressBar;
import javafx.scene.control.ProgressIndicator;
import javafx.scene.control.TextArea;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.ColumnConstraints;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

public class Main extends Application {

  private Task createWorker(final int numFiles) {
    return new Task() {
      @Override
      protected Object call() throws Exception {
        for (int i = 0; i < numFiles; i++) {
          long elapsedTime = System.currentTimeMillis();

          Thread.sleep(1 * 1000);

          elapsedTime = System.currentTimeMillis() - elapsedTime;
          String status = elapsedTime + " milliseconds";

          updateMessage(status);
          updateProgress(i + 1, numFiles);
        }
        return true;
      }
    };
  }

  private Task copyWorker;
  private int numFiles = 20;

  @Override
  public void start(Stage primaryStage) {
    final Label label = new Label("Progress:");
    final ProgressBar progressBar = new ProgressBar(0);
    final ProgressIndicator progressIndicator = new ProgressIndicator(0);

    final Button startButton = new Button("Start");
    final Button cancelButton = new Button("Cancel");
    final TextArea textArea = new TextArea();

    startButton.setOnAction((ActionEvent event) -> {
      startButton.setDisable(true);

      progressBar.setProgress(0);
      progressIndicator.setProgress(0);

      textArea.setText("");
      cancelButton.setDisable(false);

      copyWorker = createWorker(numFiles);

      progressBar.progressProperty().unbind();
      progressBar.progressProperty().bind(copyWorker.progressProperty());
      progressIndicator.progressProperty().unbind();
      progressIndicator.progressProperty().bind(copyWorker.progressProperty());

      copyWorker.messageProperty().addListener(
          (ObservableValue<? extends String> observable, String oldValue,
              String newValue) -> {
            textArea.appendText(newValue + "\n");
          });

      new Thread(copyWorker).start();
    });

    cancelButton.setOnAction((ActionEvent event) -> {
      startButton.setDisable(false);
      cancelButton.setDisable(true);
      copyWorker.cancel(true);

      progressBar.progressProperty().unbind();
      progressBar.setProgress(0);
      progressIndicator.progressProperty().unbind();
      progressIndicator.setProgress(0);
      textArea.appendText("File transfer was cancelled.");
    });

    BorderPane root = new BorderPane();
    Scene scene = new Scene(root, 500, 250, javafx.scene.paint.Color.WHITE);

    FlowPane topPane = new FlowPane(5, 5);
    topPane.setPadding(new Insets(5));
    topPane.setAlignment(Pos.CENTER);
    topPane.getChildren().addAll(label, progressBar, progressIndicator);

    GridPane middlePane = new GridPane();
    middlePane.setPadding(new Insets(5));
    middlePane.setHgap(20);
    middlePane.setVgap(20);
    ColumnConstraints column1 = new ColumnConstraints(300, 400,
        Double.MAX_VALUE);
    middlePane.getColumnConstraints().addAll(column1);
    middlePane.setAlignment(Pos.CENTER);
    middlePane.add(textArea, 0, 0);

    FlowPane bottomPane = new FlowPane(5, 5);
    bottomPane.setPadding(new Insets(5));
    bottomPane.setAlignment(Pos.CENTER);
    bottomPane.getChildren().addAll(startButton, cancelButton);

    root.setTop(topPane);
    root.setCenter(middlePane);
    root.setBottom(bottomPane);

    primaryStage.setScene(scene);
    primaryStage.show();
  }

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