Textarea scrollpane hold in text append

Question

It is my test code of textarea append text,

 public class TextAreaScrollHold extends Application {

    TextArea area = new TextArea();

    @Override
    public void start(Stage primaryStage) {
        StackPane root = new StackPane();
        root.getChildren().add(area);

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
        addTextInTextArea();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }

    public void addTextInTextArea() {
        for (int i = 0; i < 15; i++) {
            area.appendText("Hello World " + i + "\n");
        }

        Task<Void> task = new Task() {
            @Override
            protected Void call() throws Exception {
                for (int i = 15; i < 100; i++) {
                    area.appendText("Hello World " + i + "\n");
                    Thread.sleep(1000);
                }

                return null;
            }
        };
        new Thread(task).start();
    }

}

It my code data will update in thread. i need how to hold in scroll bar when data update in textarea. I have ref JavaFX TextArea and autoscroll and Access to TextArea's Scroll Pane or Scroll Bars but how solve this problems.

I need

• When data update in textarea, i will scroll the text area scrollbar the bar will hold.

  textArea.scrollTopProperty().addListener(new ChangeListener<Number>() {
              @Override
      public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
                      textArea.setScrollTop(100);
              }
          });
  

I have used this code but scroll bar in not moved bar will fixed in pixel 100 positions

Answer 1

You can use getCaretPostion and postionCaret (yes, that setter's method name is awkward for Java).

I quickly drafted up some code for you, use the scroll lock button to enable/disable scrolling:

import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.control.ToggleButton;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class ConsoleDemo extends Application {

    Console console = new Console();

    @Override
    public void start(Stage primaryStage) {

        StackPane root = new StackPane();
        root.getChildren().add(console);

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Console Demo");
        primaryStage.setScene(scene);
        primaryStage.show();

        addTextInTextArea();
    }

    /**
     * @param args
     *            the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }

    public void addTextInTextArea() {
        for (int i = 0; i < 15; i++) {
            console.log("Hello World " + i);
        }

        Task<Void> task = new Task() {
            @Override
            protected Void call() throws Exception {
                for (int i = 15; i < 100; i++) {
                    console.log("Hello World " + i);
                    Thread.sleep(1000);
                }

                return null;
            }
        };
        new Thread(task).start();

    }

    public class Console extends BorderPane {

        TextArea textArea = new TextArea();
        int scrollLockPos = -1;

        public Console() {

            HBox toolbar = new HBox();

            ToggleButton scrollLockButton = new ToggleButton("Scroll Lock");

            scrollLockButton.setOnAction(e -> {
                if (scrollLockButton.isSelected()) {
                    scrollLockPos = textArea.getCaretPosition();
                } else {
                    scrollLockPos = -1;
                }
            });

            HBox.setMargin(scrollLockButton, new Insets(5, 5, 5, 5));
            toolbar.getChildren().add(scrollLockButton);

            setCenter(textArea);
            setTop(toolbar);

        }

        public void log(String text) {

            textArea.appendText(text + "\n");

            if (scrollLockPos != -1) {
                textArea.positionCaret(scrollLockPos);
            }
        }
    }
}

Not the nicest solution, but unless you want to use selection in the textarea while it's scrolling is locked, this one works. For a proper solution you'd need access to the skin / scrollpane / scrollbars and with the upcoming Java 9 version and its modularization you don't know what you will have access to since access to them is currently flagged as "restricted".

---

Edit:

Here's an alternate solution which uses the Range, console component only. With this version you can select text and keep the selection while the Scroll Lock button is down:

import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.control.Button;
import javafx.scene.control.IndexRange;
import javafx.scene.control.TextArea;
import javafx.scene.control.ToggleButton;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;

/**
 * Console which provides a mechanism to lock scrolling. Selecting text and copying it works while scrolling is locked.
 */
public class Console extends BorderPane {

    TextArea textArea = new TextArea();
    ToggleButton scrollLockButton;
    IndexRange range;

    public Console() {

        initComponents();

    }

    private void initComponents() {

        // toolbar
        HBox toolbar = new HBox();
        toolbar.setAlignment(Pos.CENTER_RIGHT);

        // clear
        Button clearButton = new Button("Clear");
        clearButton.setOnAction(e -> {
            textArea.clear();
        });

        // scroll lock
        scrollLockButton = new ToggleButton("Scroll Lock");

        // button positions & layout
        Insets insets = new Insets(5, 5, 5, 5);
        HBox.setMargin(clearButton, insets);
        HBox.setMargin(scrollLockButton, insets);

        toolbar.getChildren().addAll(clearButton,scrollLockButton);

        // component layout
        setCenter(textArea);
        setTop(toolbar);

    }


    public void log(String text) {

        if (scrollLockButton.isSelected()) {
            range = textArea.getSelection();
        }

        textArea.appendText(text + "\n");

        if (scrollLockButton.isSelected()) {
            textArea.selectRange(range.getStart(), range.getEnd());
        }
    }
}