Question

以下代码呈现JButton没有文字：

public abstract class Test {

    public static void main(String... args) {

        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        }

        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame();
            JPanel panel = new JPanel();

            String text = "Invisible";
            JButton button = new JButton(text); // blank button rendered ???

            System.out.println(button.getText()); // prints Invisible

            button.setAction(new AbstractAction() {     
                @Override
                public void actionPerformed(ActionEvent arg0) {
                    // do nothing
                }
            });

            System.out.println(button.getText()); // prints null ???

            button.setFocusable(false);

            button.setPreferredSize(new Dimension(100, 40));

            panel.add(button);

            frame.setResizable(false);
            frame.getContentPane().add(panel);

            frame.pack();
            frame.setVisible(true);

        });

    }

}

如果我删除了对button.setAction(...)的调用，则会显示包含文字的按钮。

可替换地：

public abstract class Test {

    public static void main(String... args) {

        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        }

        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame();
            JPanel panel = new JPanel();

            String text = "Invisible";
            JButton button = null;
            button = new JButton(new AbstractAction() {     
                @Override
                public void actionPerformed(ActionEvent arg0) {
                    // do nothing
                }
            });

            button.setText(text); // renders the button with text
            System.out.println(button.getText()); // prints Invisible obviously

            button.setFocusable(false);

            button.setPreferredSize(new Dimension(100, 40));

            panel.add(button);

            frame.setResizable(false);
            frame.getContentPane().add(panel);

            frame.pack();
            frame.setVisible(true);

        });

    }

}

工作正常但有一些令人讨厌的含义，例如无法更改按钮操作而不会在之后重置其文本。

为什么？！

Answer 1

@Dima Maligin

不是答案，将被删除
应声明Swing Action（也可以覆盖isEnabled，它可以是重要的）

 private class SwingAction extends AbstractAction {

   //or public Action SwingAction() {
   //       return new AbstractAction("Invisible") {
   //           here to override AbstractAction   
   //       } 
   //    } 

    public SwingAction() {
        putValue(NAME, "Invisible"); // bounds properties
        putValue(SHORT_DESCRIPTION, "Invisible");
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // do nothing
    }
}

Answer 2

最好在JButton构造函数中输入文本，因为JButton构造函数具有字符串而不是字符串变量的参数。

JButton button = new JButton("Invisible");

Java JButton.setAction（...）null的按钮文本

2 个答案: