Question

我正在制作一个游戏引擎而且一度陷入困境。

g.drawImage(BPaint.g2dToImage(bgo.render()), 100, 100, null);

执行NullPointerException，即使我检查连接到Image参数的所有内容。该代码用于paintComponent（Graphics）方法，如下所示。

@Override
public void paintComponent(Graphics g){
    g2d = (Graphics2D) g;
    g2d.setColor(Color.BLACK);
    g2d.fillRect(0, 0, getWidth(), getHeight());
    BWindow current = BWindow.getCurrentBWindow();
    if (current != null) {
        for (BGO bgo : current.getBGOs().getBgos()) {
            g.drawImage(BPaint.g2dToImage(bgo.render()), 100, 100, null);
        }
    }
}

这是非常向前的，但是在阅读2种方法时你可能会陷入困境--bgo.render（）和BPaint.g2dToImage。

BGO是游戏对象，具有Graphics2d方法

public Graphics2D render(){
    if (bgsu == null) {
        return sprite.getGraphics();
    } else {
        return bgsu.getRule();
    }
}

忽略BGSU，因为它是null，并且没有使用，sprite是一个包含我想要获得的Graphics2D的对象。现在转到BPaint.g2dToImage（Graphics2D），这是一种将Graphics2D转换为Image的方法。

public static Image g2dToImage(Graphics2D g){
    JLabel j = new JLabel();
    j.paintAll(g);
    return j.createImage(null);
}

在检查了所有不应该为空的内容之后，我真的不知道原因。我希望你能告诉我。下面是NPE的完整堆栈跟踪。（第34行是开头的方法行）

java.lang.NullPointerException
at sun.awt.image.ImageRepresentation.startProduction(ImageRepresentation.java:732)
at sun.awt.image.ImageRepresentation.drawToBufImage(ImageRepresentation.java:807)
at sun.java2d.pipe.DrawImage.copyImage(DrawImage.java:1021)
at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:3318)
at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:3296)
at bdk.bjgl.components.BGraphics.paintComponent(BGraphics.java:34)
at javax.swing.JComponent.paint(JComponent.java:1056)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1572)
at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1495)
at javax.swing.RepaintManager.paint(RepaintManager.java:1265)
at javax.swing.JComponent._paintImmediately(JComponent.java:5167)
at javax.swing.JComponent.paintImmediately(JComponent.java:4978)
at javax.swing.RepaintManager$4.run(RepaintManager.java:824)
at javax.swing.RepaintManager$4.run(RepaintManager.java:807)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:807)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:782)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:731)
at javax.swing.RepaintManager.access$1300(RepaintManager.java:64)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1720)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

没有null对象的Graphics2d.drawImage（）的NullPointerException

0 个答案: