JSlider 个性化

然后用鼠标随便调整下窗口大小，那个设置的图片就出来了：

其中的关键代码是：

如果把null改成JComponent c：

则会抛出异常：

这个ImageObserver在作怪！而我于是去查new Painter<JComponent>() {
public void paint(Graphics2D g, JComponent c, int w, int h)的API，对于JComponent c里面说到：
Generally, to enhance reusability, most standard Painters ignore this parameter. They can thus be reused in any context. The object may be null. Implementations must not throw a NullPointerException if the object parameter is null.
也就是说JComponent c可以为null。所以这种情况该如何是好啊，怎么才能正常的显示drawImage画出的图片啊！！！！
后查明，是Toolkit的getImage的原因。使用 ImageIO的read方法就正常：

package com.han;import java.awt.BasicStroke;import java.awt.BorderLayout;import java.awt.Color;import java.awt.Container;import java.awt.Graphics2D;import java.awt.GridLayout;import java.awt.RenderingHints;import java.awt.image.BufferedImage;import java.io.IOException;import javax.imageio.ImageIO;import javax.swing.BorderFactory;import javax.swing.JComponent;import javax.swing.JFrame;import javax.swing.JPanel;import javax.swing.JSlider;import javax.swing.Painter;import javax.swing.UIDefaults;import javax.swing.UIManager;import javax.swing.UnsupportedLookAndFeelException;import javax.swing.UIManager.LookAndFeelInfo;@SuppressWarnings("serial")public class JSlider_customized extends JFrame {public JSlider_customized() {// TODO Auto-generated constructor stubfor (LookAndFeelInfo laf : UIManager.getInstalledLookAndFeels()) {if (laf.getName().equals("Nimbus")) {try {UIManager.setLookAndFeel(laf.getClassName());} catch (ClassNotFoundException | InstantiationException| IllegalAccessException| UnsupportedLookAndFeelException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}JPanel panel = new JPanel(new GridLayout(0, 1, 20, 20));JSlider slider = new JSlider(0, 100, 50);Container c = getContentPane();c.add(panel, BorderLayout.CENTER);panel.setBackground(Color.DARK_GRAY);panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));panel.add(slider);UIDefaults sliderDefaults = new UIDefaults();sliderDefaults.put("Slider.thumbWidth", 20);sliderDefaults.put("Slider.thumbHeight", 20);sliderDefaults.put("Slider:SliderThumb.backgroundPainter",new Painter<JComponent>() {public void paint(Graphics2D g, JComponent c, int w, int h) {g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);g.setStroke(new BasicStroke(2f));g.setColor(Color.RED);g.fillOval(1, 1, w - 3, h - 3);g.setColor(Color.WHITE);g.drawOval(1, 1, w - 3, h - 3); BufferedImage img;try {img = ImageIO.read(this.getClass() // this --> new Painter()内部类但是也与JSlider_customized在同一文件夹 .getResource("/images/Luxun.jpg"));g.drawImage(img, 0, 0, w, h, c); // the same for the BufferedImage when using g.drawImage(img, 0, 0, w, h, null);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();} }});sliderDefaults.put("Slider:SliderTrack.backgroundPainter",new Painter<JComponent>() {public void paint(Graphics2D g, JComponent c, int w, int h) {g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);g.setStroke(new BasicStroke(2f));g.setColor(Color.GRAY);g.fillRoundRect(0, 6, w - 1, 8, 8, 8);g.setColor(Color.WHITE);g.drawRoundRect(0, 6, w - 1, 8, 8, 8);}});slider.putClientProperty("Nimbus.Overrides", sliderDefaults);slider.putClientProperty("Nimbus.Overrides.InheritDefaults", false);JSlider slider2 = new JSlider(0, 100, 50);panel.add(slider2);}/** * @param args */public static void main(String[] args) {// JFrame.setDefaultLookAndFeelDecorated(true);JSlider_customized frame = new JSlider_customized();// frame.setUndecorated(true);// frame.getRootPane().setWindowDecorationStyle(JRootPane.FRAME);frame.pack();// leaves the frame layout manager in charge of the frame// size, so that all its contents are at or above their// preferred sizes// frame.setLocation(100, 100); // set the frame locationframe.setLocationRelativeTo(null); // centers a frame onscreenframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setVisible(true);}}

Toolkit 的getImage 都要和MediaTracker搭配使用。BufferedImage在drawImage时是全部Loaded的，此时指定ImageObserver以及设置为null是一样的效果。