java - 从内部 Action 类调用外部类的方法 getContentPane()

Question

我想从内部 Action 类调用外部类的方法 getContentPane()。我不明白为什么我的代码不起作用。

public class MainFrame extends JFrame {
    public MainFrame() {
        super("My app");
        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);

        JMenu myMenu = new JMenu("File");
        menuBar.add(myMenu);
        Action myAction = new AbstractAction("Do everything") {
            public void actionPerformed(ActionEvent e) {
                JPanel panel = new JPanel();
                panel.setBackground(Color.CYAN);
                getContentPane().add(panel, BorderLayout.CENTER);
            }
        };
        myMenu.add(myAction);
    }
}

Answer 1

您必须在 getContentPane().add(...); 之后调用 validate(); 方法。

The validate method is used to cause a container to lay out its subcomponents again. It should be invoked when this container's subcomponents are modified (added to or removed from the container, or layout-related information changed) after the container has been displayed.