Scrollbar Events in JDK 1.0.x
Uses of a Scrollbar
- As a slider
- As a way of scrolling a window
Scrollbar Events
| SCROLL_LINE_UP | Scrolled a "line" up | |
| SCROLL_LINE_DOWN | Scrolled a "line" down | |
| SCROLL_PAGE_UP | Scrolled a "page" up | |
| SCROLL_PAGE_DOWN | Scrolled a "page" down | |
| SCROLL_ABSOLUTE | Scrolled to an absolute position |
Using a Scrollbar as a Slider
package Slider; import java.awt.Frame; import java.awt.Canvas; import java.awt.Label; import java.awt.Scrollbar; import java.awt.TextField; import java.awt.Event; import java.awt.Panel; import java.awt.GridLayout; import java.awt.Color; public class Slider extends Frame { public static void main(String[] args) { Frame f = new Slider(); f.resize(300, 200); f.show(); } public Slider() { setTitle("Slider Example"); Panel p = new Panel(new GridLayout(3, 3)); p.add(m_redCanvas); m_redCanvas.setBackground(Color.red); p.add(m_redText); p.add(m_redScroll); m_redScroll.setPageIncrement(16); p.add(m_greenCanvas); m_greenCanvas.setBackground(Color.green); p.add(m_greenText); p.add(m_greenScroll); m_greenScroll.setPageIncrement(16); p.add(m_blueCanvas); m_blueCanvas.setBackground(Color.blue); p.add(m_blueText); p.add(m_blueScroll); m_blueScroll.setPageIncrement(16); add("South", p); m_targetCanvas.setBackground(new Color(0, 0, 0)); add("Center", m_targetCanvas); } public boolean handleEvent(Event evt) { if (evt.id == Event.WINDOW_DESTROY) System.exit(0); else if (evt.id == Event.LOST_FOCUS) { int value; if (evt.target == m_redText) { value = Integer.parseInt(m_redText.getText()); m_redScroll.setValue(value); } else if (evt.target == m_greenText) { value = Integer.parseInt(m_greenText.getText()); m_greenScroll.setValue(value); } else if (evt.target == m_blueText) { value = Integer.parseInt(m_blueText.getText()); m_blueScroll.setValue(value); } } else if (evt.id == Event.SCROLL_ABSOLUTE || evt.id == Event.SCROLL_LINE_DOWN || evt.id == Event.SCROLL_LINE_UP || evt.id == Event.SCROLL_PAGE_DOWN || evt.id == Event.SCROLL_PAGE_UP ) { int red = m_redScroll.getValue(); int green = m_greenScroll.getValue(); int blue = m_blueScroll.getValue(); m_redText.setText("" + red); m_greenText.setText("" + green); m_blueText.setText("" + blue); m_targetCanvas.setBackground(new Color(red, green, blue)); m_targetCanvas.repaint(); return true; } return super.handleEvent(evt); } //////////// Data ////////////// private Canvas m_redCanvas = new Canvas(); private Canvas m_greenCanvas = new Canvas(); private Canvas m_blueCanvas = new Canvas(); private TextField m_redText = new TextField("0"); private TextField m_greenText = new TextField("0"); private TextField m_blueText = new TextField("0"); private Scrollbar m_redScroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 0, 0, 255); private Scrollbar m_greenScroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 0, 0, 255); private Scrollbar m_blueScroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 0, 0, 255); private Canvas m_targetCanvas = new Canvas(); }
Using a Scrollbar to Scroll a Window
Beware! The scrolling behavior is quite flaky!
package Scroller; import java.awt.Scrollbar; import java.awt.Canvas; import java.awt.Frame; import java.awt.Event; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Point; import java.awt.Label; import java.awt.Color; public class Scroller extends Frame { public static void main(String[] args) { Frame f = new Scroller(); f.resize(300, 200); f.show(); } public Scroller() { setTitle("Scroller Example"); add("North", m_position); m_position.setBackground(Color.lightGray); add("East", m_verScroll); add("South", m_horScroll); add("Center", m_canvas); } public void show() { super.show(); reScale(0, 0); reportPosition(); } public boolean handleEvent(Event evt) { if (evt.id == Event.WINDOW_DESTROY) System.exit(0); else if (evt.id == Event.WINDOW_MOVED || evt.id == Event.WINDOW_EXPOSE ) { reScale(m_horScroll.getValue(), m_verScroll.getValue()); reportPosition(); } else if (evt.id == Event.SCROLL_ABSOLUTE || evt.id == Event.SCROLL_LINE_DOWN || evt.id == Event.SCROLL_LINE_UP || evt.id == Event.SCROLL_PAGE_DOWN || evt.id == Event.SCROLL_PAGE_UP ) { m_canvas.translate(m_horScroll.getValue(), m_verScroll.getValue()); reportPosition(); return true; } return super.handleEvent(evt); } private void reScale(int x, int y) { Dimension d = m_canvas.size(); m_horScroll.setValues(x, d.width, 0, m_canvas.WIDTH); m_horScroll.setVisible(d.width < m_canvas.WIDTH); m_verScroll.setValues(y, d.height, 0, m_canvas.HEIGHT); m_verScroll.setVisible(d.height < m_canvas.HEIGHT); } private void reportPosition() { int hMax = m_horScroll.getMaximum(); int vMax = m_verScroll.getMaximum(); int hVis = m_horScroll.getVisible(); int vVis = m_verScroll.getVisible(); int hPos = m_horScroll.getValue(); int vPos = m_verScroll.getValue(); m_position.setText("Max = [" + hMax + "," + vMax + "] Visible = [" + hVis + "," + vVis + "] Position = [" + hPos + "," + vPos + "]"); } /////////// Data /////////// private Label m_position = new Label(""); private Scrollbar m_verScroll = new Scrollbar(Scrollbar.VERTICAL); private Scrollbar m_horScroll = new Scrollbar(Scrollbar.HORIZONTAL); private CanvasOfSquares m_canvas = new CanvasOfSquares(); } class CanvasOfSquares extends Canvas { public static final int HEIGHT = 400; public static final int WIDTH = 600; public CanvasOfSquares() { for (int i = 0; i < m_square.length; i++) { int x = (int)(Math.random() * WIDTH); int y = (int)(Math.random() * HEIGHT); m_square[i] = new Point(x, y); } } public void translate(int x, int y) { m_dx = x; m_dy = y; repaint(); } public void paint(Graphics g) { g.translate(-m_dx, -m_dy); for (int i = 0; i < m_square.length; i++) draw(g, i); } public void draw(Graphics g, int i) { g.drawRect(m_square[i].x, m_square[i].y, SQUARESIZE, SQUARESIZE); } /////////////// Data /////////////// private static final int SQUARESIZE = 10; private static final int MAXSQUARECOUNT = 100; private int m_dx = 0; private int m_dy = 0; private int m_squareCount = 0; private Point[] m_square = new Point[MAXSQUARECOUNT]; private int m_current = -1; }
