DefaultListCellRenderer 工作正常但无法让 ListCellRenderer 工作

Question

我已经尝试扩展 DefaultListCellRenderer 以更改文本颜色，它工作正常 be.But 我无法显示 JList 我是 rendering.Then 我尝试实施 ListCellRenderer，但我什至无法显示 JList 的内容。我已经在鼠标点击 JList 时设置了渲染器，在 ListCellRenderer 的情况下，列表在鼠标点击时消失，但在 DefaultListCellRenderer 的情况下它工作正常。

我的第一个问题是为什么 JList 的内容在单击鼠标时消失，第二个问题是为什么我无法通过添加以下代码来添加图标 DefaultListCellRenderer。

ImageIcon imageIcon = new ImageIcon(getClass().getResource("/images/im.png"));
setIcon(imageIcon);

以下是渲染器的全部代码。

public class RCellRenderer extends JLabel implements ListCellRenderer {

    String runm = "";

    public RCellRenderer(String runm) {
        this.runm = runm;

    }

    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
    //    Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);

        if (value.equals(runm)) {
            Color fg = Color.BLACK;
            setForeground(fg);
        }

     //   return c;
     return this;
    }

}

DefaultListCellRenderer的代码如下：

public class RCellRenderer extends DefaultListCellRenderer {

    String runm = "";

    public RCellRenderer(String runm) {
        this.runm = runm;

    }

    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
        Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
        ImageIcon imageIcon = new ImageIcon(getClass().getResource("images/in.png"));

        setIcon(imageIcon);
        if (value.equals(runm)) {
            Color fg = Color.BLACK;
            setForeground(fg);
        }

        return c;
    }

}

在我的程序中执行此操作时的堆栈跟踪如下：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.ImageIcon.<init>(ImageIcon.java:217)
    at services.RCellRenderer.getListCellRendererComponent(RCellRenderer.java:29)
    at javax.swing.plaf.basic.BasicListUI.updateLayoutState(BasicListUI.java:1361)
    at javax.swing.plaf.basic.BasicListUI.maybeUpdateLayoutState(BasicListUI.java:1311)
    at javax.swing.plaf.basic.BasicListUI.getCellBounds(BasicListUI.java:952)
    at javax.swing.plaf.basic.BasicListUI$Handler.repaintCellFocus(BasicListUI.java:2807)
    at javax.swing.plaf.basic.BasicListUI$Handler.focusLost(BasicListUI.java:2823)
    at java.awt.Component.processFocusEvent(Component.java:6425)
    at java.awt.Component.processEvent(Component.java:6289)
    at java.awt.Container.processEvent(Container.java:2237)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2295)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1954)
    at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:1024)
    at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:690)
    at java.awt.Component.dispatchEventImpl(Component.java:4760)
    at java.awt.Container.dispatchEventImpl(Container.java:2295)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at sun.awt.SunToolkit.run(SunToolkit.java:518)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
    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)

Answer 1

您试图通过从 JLabel 扩展来从头开始实现 ListCellRenderer 接口（而不是从 DefaultListCellRenderer 又从 JLabel).

延伸

因此你需要实现所有的方法 DefaultListCellRenderer.getListCellRendererComponent 确实如此，最重要的是，这涉及将 value 传递给此方法并将其放入 JLabel.setText 调用中。

简而言之，我建议您从 DefaultListCellRenderer:

扩展您的渲染器

public class RCellRenderer extends DefaultListCellRenderer {

    String runm = "";

    public RCellRenderer2(String runm) {
        this.runm = runm;
    }

    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
        Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);

        if (value.equals(runm)) {
            Color fg = Color.BLACK;
            c.setForeground(fg);
        }

        return c;
    }
}

Answer 2

我刚刚删除了 getClass().getResource(...)，它工作得很好。我不知道为什么，但就是这样。工作代码如下

public class RCellRenderer extends DefaultListCellRenderer {

    String runm = "";

    public RCellRenderer(String runm) {
        this.runm = runm;

    }

    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
        Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
        ImageIcon imageIcon = new ImageIcon("images/in.png");
        setIcon(imageIcon);
        if (value.equals(runm)) {
            Color fg = Color.BLACK;
            setForeground(fg);
        }

        return c;
    }

}

在这个问题解决后我还有一个问题，这张图片可以添加到JList的最右边吗？

DefaultListCellRenderer 工作正常但无法让 ListCellRenderer 工作

DefaultListCellRenderer working fine but could not get ListCellRenderer to work

java

icons

swing

renderer