Swing：如何让JFrame滚动流畅？

Question

I'm creating a very simple Swing GUI consisting of a scrollable text area. However, I'm having some problems with the responsiveness of the UI. Here is the class I am using to try some different configurations:

public class ComponentSample {
  public void createWindow() {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    TextArea textArea = new TextArea(getFillerText(), 40, 120);

    setViews(frame, textArea);

    frame.pack();
    frame.setVisible(true);
  }

  private void setViews(JFrame frame, TextArea textArea) {
    ...
  }

  private String getFillerText() {
    String threeLines = "Why isn't scrolling smooth? \nSteve Jobs would not approve\n\n";
    StringBuilder stringBuilder = new StringBuilder();
    for (int i = 0; i < 100; i++) {
      stringBuilder.append(threeLines);
    }
    return stringBuilder.toString();
  }

  public static void main(String[] args) throws Exception {
    SwingUtilities.invokeLater(
      () -> new ComponentSample().createWindow()
    );
  }
}

Here I have tried several different method bodies for the setViews() method with the following results:

Adding textArea in a JPanel

    JPanel panel = new JPanel();
    panel.add(textArea);
    frame.add(panel);

Scrolls by 1 or 2 rows instead of by pixel (not smooth). Also flashes white when scrolling quickly (repainting issue?).

Adding textArea in a Viewport

    JViewport viewport = new JViewport();
    viewport.setView(textArea);
    frame.add(viewport);

Same results as JPanel.

Adding textArea directly

    frame.add(textArea);

Same results as JPanel.

Adding textArea in a ScrollPane

    JScrollPane scrollPane = new JScrollPane(textArea);
    scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED);
    frame.add(scrollPane);

Doesn't seem to handle scrolling properly - it doesn't respond to the scrollwheel (only clicking the scrollbar). Scrolls by ~0.5 row instead of by pixel.

Also, in each of the above cases, when the scrollbar is dragged with the mouse it prints the following (error? IDEA shows it in red) to the stdout:

2016-03-17 09:45:33.413 java[40977:2845515] inOptions: {
    JavaCUIThumbStartKey = 0;
    "is.flipped" = 0;
    kCUIOrientationKey = kCUIOrientVertical;
    kCUIThumbProportionKey = "0.1328903585672379";
    max = 0;
    pressedpart = 0;
    state = normal;
    value = 0;
    widget = scrollbar;
}
2016-03-17 09:45:33.413 java[40977:2845515] inOptions: {
    JavaCUIThumbStartKey = 0;
    "is.flipped" = 0;
    kCUIOrientationKey = kCUIOrientVertical;
    kCUIThumbProportionKey = "0.1328903585672379";
    max = 0;
    pressedpart = 0;
    state = normal;
    value = 0;
    widget = scrollbar;
}
2016-03-17 09:45:33.414 java[40977:2845515] outHitPart = 0

If it matters, I'm on OS X.

My question is how can I make it scroll smoothly (pixel by pixel) without flashing white and without printing errors?

Answer 1

Don't use a TextArea that is an AWT component.

Instead you should be using a JTextArea which is the Swing component.

The basic code is:

JTextArea textArea = new JTextArea(5, 20);
JScrollPane scrollPane = new JScrollPane( textArea );
frame.add( scrollPane );

Edit:

it still scrolls by full rows instead of by pixel

A scroll pane support the concept of unit scrolling and block scrolling. Unit scrolling for a JTextArea is one row of text and block scrolling is the size of the viewport window. When using a mouse the scrolling (in windows) is based on a multiple of the unit scrolling which on my component is 3 * the unit scrolling.

If your concern is the amount of scrolling done by the mouse wheel then maybe you can use the Mouse Wheel Controller which allows you to change the multiplier to a different value. So you could set it to 1.

If you concern is the actual unit increment amount then you can change the default by using:

scrollPane.getVerticalScrollBar().setUnitIncrement(1);

Answer 2

As camickr pointed out, I should have been using a JTextArea instead of a TextArea . That fixed the white flashes which I assume were repaint issues.

To make scrolling smooth without being laggy, I had to adjust the unit increment, which is the number of pixels the view will move by when one of the scrollbar arrows is pressed:

scrollPane.getVerticalScrollBar().setUnitIncrement(1);

This ended up causing a bunch of lag because when I scrolled the program had to continuously calculate and redraw the screen at 1px intervals. To fix this, I had to change the viewport scroll mode:

scrollPane.getViewport().setScrollMode(JViewport.BACKINGSTORE_SCROLL_MODE);

It turns out it was using BLIT_SCROLL_MODE by default.

What I have now is an app that scrolls smoothly (doesn't jump pixels), doesn't lag and doesn't flash white when I scroll too fast. That's pretty good progress. The one thing I haven't managed to figure out is that now scrolling is fairly slow - eg giving the mouse wheel a good spin doesn't get me too far down the page. This is obviously because I'm only moving one pixel per notch (that's what setUnitIncrement() did). What I want is to go a good distance down the page when I scroll agressively, just like in other apps like Chrome or Intellij. But for now I'm pretty happy with where I've got it.