我正在尝试使用以下代码将图标（javax.swing.Icon）转换为图片（java.awt.Image）：
private Image iconToImage(Icon icon)
{
if(icon instanceof ImageIcon)
{
return ((ImageIcon) icon).getImage();
}
else
{
BufferedImage image = new BufferedImage(icon.getIconWidth(), icon.getIconHeight(), BufferedImage.TYPE_INT_RGB);
icon.paintIcon(null, image.getGraphics(), 0, 0);
return image;
}
}
问题是，paintIcon函数会在NullPointerException上抛出image.getGraphics()。
对于记录，icon值是默认的CheckBox图标（通过UIManager.getIcon("CheckBox.icon")获得）
以下是抛出异常的详细信息：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.sun.java.swing.plaf.windows.WindowsIconFactory$CheckBoxIcon.paintIcon(WindowsIconFactory.java:306)
at utils.WarningRenderer.iconToImage(WarningRenderer.java:50)
at utils.WarningRenderer.<init>(WarningRenderer.java:38)
at deliveryexpress.DeliveryExpressView.setWarnings(DeliveryExpressView.java:278)
at deliveryexpress.DeliveryExpressView.updateLists(DeliveryExpressView.java:218)
at deliveryexpress.DeliveryExpressView.access$1100(DeliveryExpressView.java:47)
at deliveryexpress.DeliveryExpressView$5.addCheck(DeliveryExpressView.java:183)
at org.japura.gui.model.DefaultListCheckModel.fireCheckListModelListeners(Unknown Source)
at org.japura.gui.model.DefaultListCheckModel.fireAddCheckListModelListeners(Unknown Source)
at org.japura.gui.model.DefaultListCheckModel.addCheck(Unknown Source)
at org.japura.gui.CheckList$1.mouseClicked(Unknown Source)
at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:253)
at java.awt.Component.processMouseEvent(Component.java:6292)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6054)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4652)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4482)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4247)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4482)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:644)
at java.awt.EventQueue.access$000(EventQueue.java:85)
at java.awt.EventQueue$1.run(EventQueue.java:603)
at java.awt.EventQueue$1.run(EventQueue.java:601)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:617)
at java.awt.EventQueue$2.run(EventQueue.java:615)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:614)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
如果您需要更多详细信息，请告诉我，我会编辑我的帖子以添加它们。
谢谢！
答案 0 :(得分：15)
刚刚找到一个代码片段，如果你想更频繁地包装那些行为不端的LAF提供的图标，那么它可能会有所帮助：
/**
* Some ui-icons misbehave in that they unconditionally class-cast to the
* component type they are mostly painted on. Consequently they blow up if
* we are trying to paint them anywhere else (f.i. in a renderer).
*
* This Icon is an adaption of a cool trick by Darryl Burke/Rob Camick found at
* http://tips4java.wordpress.com/2008/12/18/icon-table-cell-renderer/#comment-120
*
* The base idea is to instantiate a component of the type expected by the icon,
* let it paint into the graphics of a bufferedImage and create an ImageIcon from it.
* In subsequent calls the ImageIcon is used.
*
*/
public static class SafeIcon implements Icon {
private Icon wrappee;
private Icon standIn;
public SafeIcon(Icon wrappee) {
this.wrappee = wrappee;
}
@Override
public int getIconHeight() {
return wrappee.getIconHeight();
}
@Override
public int getIconWidth() {
return wrappee.getIconWidth();
}
@Override
public void paintIcon(Component c, Graphics g, int x, int y) {
if (standIn == this) {
paintFallback(c, g, x, y);
} else if (standIn != null) {
standIn.paintIcon(c, g, x, y);
} else {
try {
wrappee.paintIcon(c, g, x, y);
} catch (ClassCastException e) {
createStandIn(e, x, y);
standIn.paintIcon(c, g, x, y);
}
}
}
/**
* @param e
*/
private void createStandIn(ClassCastException e, int x, int y) {
try {
Class<?> clazz = getClass(e);
JComponent standInComponent = getSubstitute(clazz);
standIn = createImageIcon(standInComponent, x, y);
} catch (Exception e1) {
// something went wrong - fallback to this painting
standIn = this;
}
}
private Icon createImageIcon(JComponent standInComponent, int x, int y) {
BufferedImage image = new BufferedImage(getIconWidth(),
getIconHeight(), BufferedImage.TYPE_INT_ARGB);
Graphics g = image.createGraphics();
try {
wrappee.paintIcon(standInComponent, g, 0, 0);
return new ImageIcon(image);
} finally {
g.dispose();
}
}
/**
* @param clazz
* @throws IllegalAccessException
*/
private JComponent getSubstitute(Class<?> clazz) throws IllegalAccessException {
JComponent standInComponent;
try {
standInComponent = (JComponent) clazz.newInstance();
} catch (InstantiationException e) {
standInComponent = new AbstractButton() {
};
((AbstractButton) standInComponent).setModel(new DefaultButtonModel());
}
return standInComponent;
}
private Class<?> getClass(ClassCastException e) throws ClassNotFoundException {
String className = e.getMessage();
className = className.substring(className.lastIndexOf(" ") + 1);
return Class.forName(className);
}
private void paintFallback(Component c, Graphics g, int x, int y) {
g.drawRect(x, y, getIconWidth(), getIconHeight());
g.drawLine(x, y, x + getIconWidth(), y + getIconHeight());
g.drawLine(x + getIconWidth(), y, x, y + getIconHeight());
}
}
要在您的代码段中使用，只需传入一个任意组件：
icon = new SafeIcon(icon);
BufferedImage image = new BufferedImage(icon.getIconWidth(), icon.getIconHeight(), BufferedImage.TYPE_INT_RGB);
icon.paintIcon(new JPanel(), image.getGraphics(), 0, 0);
答案 1 :(得分：8)
试试这个：
static Image iconToImage(Icon icon) {
if (icon instanceof ImageIcon) {
return ((ImageIcon)icon).getImage();
}
else {
int w = icon.getIconWidth();
int h = icon.getIconHeight();
GraphicsEnvironment ge =
GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gd = ge.getDefaultScreenDevice();
GraphicsConfiguration gc = gd.getDefaultConfiguration();
BufferedImage image = gc.createCompatibleImage(w, h);
Graphics2D g = image.createGraphics();
icon.paintIcon(null, g, 0, 0);
g.dispose();
return image;
}
}
一个完整的示例，我们使用laf提供的图标，将其转换为图像并在Windows系统托盘上使用它。
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import javax.swing.*;
public class SysTrayDemo {
protected static TrayIcon trayIcon;
private static PopupMenu createTrayMenu() {
ActionListener exitListener = new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("Bye from the tray");
System.exit(0);
}
};
ActionListener executeListener = new ActionListener() {
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog
(null, "Popup from the action on the systray!",
"User action", JOptionPane.INFORMATION_MESSAGE);
trayIcon.displayMessage
("Done", "You can do it again if you want!",
TrayIcon.MessageType.INFO);
}
};
PopupMenu menu = new PopupMenu();
MenuItem execItem = new MenuItem("Action...");
execItem.addActionListener(executeListener);
menu.add(execItem);
MenuItem exitItem = new MenuItem("Exit");
exitItem.addActionListener(exitListener);
menu.add(exitItem);
return menu;
}
/**
* using a built-in icon
* we need to convert the icon to an Image
*/
private static TrayIcon createTrayIconFromBuiltInIcon() {
Icon icon = UIManager.getIcon("OptionPane.warningIcon");
PopupMenu popup = createTrayMenu();
Image image = iconToImage(icon);
TrayIcon ti = new TrayIcon(image, "Java System Tray Demo", popup);
ti.setImageAutoSize(true);
return ti;
}
static Image iconToImage(Icon icon) {
if (icon instanceof ImageIcon) {
return ((ImageIcon)icon).getImage();
} else {
int w = icon.getIconWidth();
int h = icon.getIconHeight();
GraphicsEnvironment ge =
GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gd = ge.getDefaultScreenDevice();
GraphicsConfiguration gc = gd.getDefaultConfiguration();
BufferedImage image = gc.createCompatibleImage(w, h);
Graphics2D g = image.createGraphics();
icon.paintIcon(null, g, 0, 0);
g.dispose();
return image;
}
}
public static void main(String[] args) throws Exception {
if (!SystemTray.isSupported()) {
System.out.println
("System tray not supported on this platform");
System.exit(1);
}
try {
SystemTray sysTray = SystemTray.getSystemTray();
trayIcon = createTrayIconFromBuiltInIcon();
sysTray.add(trayIcon);
trayIcon.displayMessage("Ready",
"Tray icon started and tready", TrayIcon.MessageType.INFO);
}
catch (AWTException e) {
System.out.println("Unable to add icon to the system tray");
System.exit(1);
}
}
}
答案 2 :(得分：2)
试试这个：
icon.paintIcon(new JCheckBox(), image.getGraphics(), 0, 0);
我无法准确解释为什么它需要JCheckBox。也许这个图标有所不同？ NullPointerException来自MetalIconFactory "CheckBox.icon"中的这一行：
ButtonModel model = ((JCheckBox)c).getModel();