添加Swing菜单栏时会出现大量错误

Question

我正在使用NetBeans创建一个Java应用程序，所以我利用了GUI，但是每当我尝试添加一个swing菜单栏时，我就会得到大量的错误。你能帮我解决这个问题吗？

当在GUI构建器菜单下的"Swing菜单“中，我将”菜单栏“拖到我的JFrame的顶部(我有足够的空间用于它和所有东西)，它在GUI生成器中看起来很好(下面是屏幕截图的视图链接)。

GUI生成器菜单栏选择

​

添加菜单栏之前在GUI生成器中的JFrame

​

添加菜单栏后图形用户界面生成器中的JFrame

​

添加菜单栏后运行应用程序后的JFrame

​

在添加菜单栏之前运行应用程序后的JFrame

​

这些是我在运行带有菜单栏的应用程序时遇到的所有错误

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at java.desktop/com.apple.laf.AquaMenuPainter.paintMenuBarBackground(AquaMenuPainter.java:149)
    at java.desktop/com.apple.laf.AquaMenuBarUI.paint(AquaMenuBarUI.java:82)
    at java.desktop/javax.swing.plaf.ComponentUI.update(ComponentUI.java:161)
    at java.desktop/javax.swing.JComponent.paintComponent(JComponent.java:797)
    at java.desktop/javax.swing.JComponent.paint(JComponent.java:1074)
    at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
    at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
    at java.desktop/javax.swing.JLayeredPane.paint(JLayeredPane.java:590)
    at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
    at java.desktop/javax.swing.JComponent.paintToOffscreen(JComponent.java:5262)
    at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBufferedImpl(RepaintManager.java:1643)
    at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1618)
    at java.desktop/javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1556)
    at java.desktop/javax.swing.RepaintManager.paint(RepaintManager.java:1323)
    at java.desktop/javax.swing.JComponent.paint(JComponent.java:1060)
    at java.desktop/java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
    at java.desktop/sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:78)
    at java.desktop/sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:115)
    at java.desktop/java.awt.Container.paint(Container.java:2002)
    at java.desktop/java.awt.Window.paint(Window.java:3926)
    at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:876)
    at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:848)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
    at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:848)
    at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:823)
    at java.desktop/javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:772)
    at java.desktop/javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1884)
    at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:313)
    at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
    at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
    at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

有人知道为什么会这样吗？

Answer 1

我搜索了一下，发现(基于异常)它是由外观和感觉引起的。不知道为什么它只在添加了一个菜单的时候才会失败.

请尝试将主方法中的外观和感觉设置为如下所示。对于我来说，netbeans总是生成使用nimbus l&f的主要方法。

public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Exception e) {
            e.printStackTrace();
        }

        ...//all other stuff which was there earlier...e.g. java.awt.EventQueue.invokeLater(new Runnable()...

    }

或者，您可以尝试一下，而不是Nimbus：

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());