JProgressBar显示含小数百分比
在原生的JProgressBar中，并没提供详细控制百分比的途径。
计算百分比是由其内部维护的BoundedRangeModel所决定，而且其侦听器是重要所在。
通常情况，必须通过setValue来触发侦听器，使JProgressBar重绘百分比区域的图形。
一开始我以为此侦听器是由BoundedRangeModel内部自动绑定的，事实并非如此，毫无踪影。偶然在网上看见根据百分比而改变背景颜色，才醒悟BoundedRangeModel是数据模型，而处理图形应是ProgressBarUI。
果然，在BasicProgressBarUI里找到了此侦听器。
private class Handler implements ChangeListener, PropertyChangeListener, HierarchyListener {
// ChangeListener
public void stateChanged(ChangeEvent e) {
BoundedRangeModel model = progressBar.getModel();
int newRange = model.getMaximum() - model.getMinimum();
int newPercent;
int oldPercent = getCachedPercent();
if (newRange > 0) {
newPercent = (int)((100 * (long)model.getValue()) / newRange);
} else {
newPercent = 0;
}
if (newPercent != oldPercent) {
setCachedPercent(newPercent);
progressBar.repaint();
}
}
progressBar.repaint()将会发送一个PaintEvent通知描绘。其后接受到，便自动跳回至BasicProgressBarUI调用paint(Graphics g, JComponent c)实现描绘。
该实现描绘包含了描绘百分比方法paintString(Graphics g, int x, int y...)，核心内容如下。
private void paintString(Graphics g, int x, int y, int width, int height,
int fillStart, int amountFull, Insets b) {
if (!(g instanceof Graphics2D)) {
return;
}
Graphics2D g2 = (Graphics2D)g;
String progressString = progressBar.getString();
g2.setFont(progressBar.getFont());
Point renderLocation = getStringPlacement(g2, progressString,
x, y, width, height);
Rectangle oldClip = g2.getClipBounds();
if (progressBar.getOrientation() == JProgressBar.HORIZONTAL) {
g2.setColor(getSelectionBackground());
SwingUtilities2.drawString(progressBar, g2, progressString,
renderLocation.x, renderLocation.y);
g2.setColor(getSelectionForeground());
g2.clipRect(fillStart, y, amountFull, height);
SwingUtilities2.drawString(progressBar, g2, progressString,
renderLocation.x, renderLocation.y);
} else { // VERTICAL
g2.setColor(getSelectionBackground());
AffineTransform rotate =
AffineTransform.getRotateInstance(Math.PI/2);
g2.setFont(progressBar.getFont().deriveFont(rotate));
renderLocation = getStringPlacement(g2, progressString,
x, y, width, height);
SwingUtilities2.drawString(progressBar, g2, progressString,
renderLocation.x, renderLocation.y);
g2.setColor(getSelectionForeground());
g2.clipRect(x, fillStart, width, amountFull);
SwingUtilities2.drawString(progressBar, g2, progressString,
renderLocation.x, renderLocation.y);
}
g2.setClip(oldClip);
}
progressBar.getString()便是获取百分比字符串化的途径，但这是一个私有方法，并且多次调用了sun.swing私有类包，硬生生地耦合了JProgressBar。
大概流程：
- JProgressBar#setValue(int)
- BasicProgressBarUI.Handler#stateChanged(ChangeEvent)
- JProgressBar#repaint()
- BasicProgressBarUI#paint(Graphics,JComponent)
- BasicProgressBarUI#paintString(Graphics,int,int,int,int,int,int,Insets)
- JProgressBar#getString()
当然，如果你敢善用sun.swing私有类包，即可解决这些耦合问题，否则……
public class PercentProgressBar extends JProgressBar {
private transient NumberFormat numberFormat;
private NumberFormat createPercentFormat(){
NumberFormat nf = NumberFormat.getPercentInstance();
nf.setMinimumFractionDigits(minFractionDigits()); // also affect MaximumFractionDigits
nf.setMaximumFractionDigits(maxFractionDigits());
return nf;
}
protected int minFractionDigits() {
return 0;
}
protected int maxFractionDigits() {
return 3;
}
@Override
public String getString() {
if (progressString != null) return progressString;
if (numberFormat == null) {
numberFormat = this.createPercentFormat();
}
return numberFormat.format( getPercentComplete() );
}
@Override
public void updateUI() {
super.setUI(new BasicProgressBarUI() {
@Override
protected void installListeners() {
super.installListeners();
super.progressBar.removeChangeListener(super.changeListener);
super.changeListener = new ChangeListener() {
private final double fd = Math.pow(10, 2+maxFractionDigits());
private int cachedPercent = 0;
/**
* @see BasicProgressBarUI.Handler#stateChanged(ChangeEvent)
*/
@Override
public void stateChanged(ChangeEvent e) {
final int percent = (int) (getPercentComplete()*fd +0.5);
if(cachedPercent == percent) return; // ignore
cachedPercent = percent; // update newPercent
progressBar.repaint();
}
};
super.progressBar.addChangeListener(super.changeListener);
}
});
}
/**
* Test
*/
public static void main(String[] args) {
final JProgressBar progressBar = new PercentProgressBar();
progressBar.setFont(new java.awt.Font("Dialog", java.awt.Font.PLAIN, 20));
progressBar.setStringPainted(true);
progressBar.setMaximum( 1234567890 );
javax.swing.JFrame frame = new javax.swing.JFrame();
frame.getContentPane().add( progressBar );
frame.setSize(100, 100);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
frame.setVisible(true);
javax.swing.SwingUtilities.invokeLater(new Runnable() {
private java.util.Random random = new java.util.Random();
@Override public void run() {
int value = progressBar.getValue();
if(value >= progressBar.getMaximum()){ System.out.println("100%"); return; }
int rd = random.nextInt(1000000);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
progressBar.setValue( value+(1+rd) );
javax.swing.SwingUtilities.invokeLater(this);
}
});
}
}
附带简易测试，见截图。
