Question

我的意思是drawImage（）方法对我不起作用。人们说要做的事情

g.drawImage(image, 0, 0, null);

但是日食实际上否认了它。它说：

Graphics类型中的drawImage（Image，int，int，ImageObserver）方法不适用于参数（Image，int，int，null）

这实际上让我很困惑，我已经从其他人那里读到了一些答案，他们总是说这些答案是空的。我试图运行它，它给了我这个：

Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem: 
The method drawImage(Image, int, int, ImageObserver) in the type Graphics is not applicable for the arguments (Image, int, int, null)

at me.danielshe.graphics.DrawComponent.paintComponent(DrawComponent.java:29)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent._paintImmediately(Unknown Source)
at javax.swing.JComponent.paintImmediately(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.access$1200(Unknown Source)
at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

任何人都可以帮助我，或者这是一种放置东西而不是“null”的方法吗？我试图把“这个”，甚至实现ImageObserver。但它们都不起作用。

感谢。

Answer 1

您需要一个实现ImageObserver接口的对象。一般这将是与图形对象相关联的组件。

Answer 2

使用null作为ImageObserver没错。等效于此：

ImageObserver obs = null;

drawImage（img，x，y，obs）;

在可以使用引用（对象）的任何地方都可以使用Null。当您需要使用此引用/对象时，就会出现问题，因为对象为空，因此您将获得运行时异常。在您的示例中，只要您在调用drawImage（）时图像已完全加载，就不会有问题，因此，如果您确定图像已完全加载，则只应在drawImage（）上使用null。现在我在编译器上还没有遇到这个问题，但是我没有使用eclipse，只是使用了文本编辑器和命令行。尝试使用命令行进行编译，或者在Eclipse上使用上面两行代码。仅当您使用drawImage的类实现了ImageObserver接口或扩展了实现该类的类（例如，例如Jcomponent）时，“ this”才起作用。

致谢

Java中的“null”drawImage（）

2 个答案: