java - 按钮不显示文本区域中的文本

Question

我正在设计一个简单的 GUI(在 Eclipse 中使用 WindowBuilder Pro)，仅在按下按钮后在 textArea 中显示“Hello World”(测试)。

但是，当我按下按钮时，它没有显示在文本区域中!有人可以调整代码或者至少告诉我该怎么做吗？

public class TextA {

private JFrame frame;


/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                TextA window = new TextA();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public TextA() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);

    JTextArea textArea = new JTextArea();
    textArea.setBounds(113, 44, 226, 96);
    frame.getContentPane().add(textArea);

    JButton btnTesting = new JButton("Testing");
    btnTesting.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {

            JTextArea textArea = new JTextArea();
            textArea.setText("Hello World!");


        }
    });
    btnTesting.setBounds(168, 167, 117, 29);
    frame.getContentPane().add(btnTesting);
}
}

Answer 1

将您的代码更改为类似这样的内容。

 final JTextArea textArea = new JTextArea();
 frame.getContentPane().add(textArea);
 btnTesting.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            textArea.setText("Hello World!");
        }
    });

您正在 actionListener 内创建一个新实例，您希望引用要添加到框架中的对象。正如 @AndrewThompson 总是建议不要使用 null 布局原因:

Java GUIs might have to work on a number of platforms, on different screen resolutions & using different PLAFs. As such they are not conducive to exact placement of components. To organize the components for a robust GUI, instead use layout managers, or combinations of them, along with layout padding & borders for white space.