java - JTextField - setColumns() 方法对我不起作用

Question

我的问题是我的 JTextField -setColumns(int)

“field1.setColumns(5);”

...不起作用。我猜这是一个布局管理器问题。但是，我正在从一本练习册中学习。我知道的唯一布局是 flowLayout、borderLayout 和 gridlayout。

简而言之，只要“field2”触发 ActionEvent(通过按回车键)，“field1”就应该改变大小。

我在“actionPerformed”中放置了一个“System.out.println(”ActionEvent detected”) 以证明正在触发一个 Action 事件，所以这不是问题。我什至打印了“field1.getColumn "并且它显示了正确的更改值 5，但是......它不仅在运行时没有明显改变大小。

我希望有人能解释这个问题，而不是解决问题。变通并不能帮助我学习，而这正是解决这些书本练习的全部目的。

如果它很重要，我将使用 netbeans 进行编码。预先感谢您的帮助。

public class Exercise13_11 extends JFrame implements ActionListener
{
    private JTextField textField1, textField2;
    private JLabel label1, label2;
    private JRadioButton rButton1, rButton2, rButton3;

    public static void main(String[] args)
    {
        JFrame frame = new Exercise13_11();
        frame.setTitle("Exercise 13.11");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(450, 200);
        frame.setVisible(true);
    }

public Exercise13_11()
{
    // North Panel aligned and filled.
    JPanel northPanel = new JPanel();
    northPanel.setLayout(new FlowLayout(FlowLayout.CENTER));
    northPanel.add(label1 = new JLabel("Text Field"));
    northPanel.add(textField1 = new JTextField(20));
    northPanel.setToolTipText("Demonstrate JTextField");
    getContentPane().add(northPanel, BorderLayout.CENTER);

    // South panel now being filled...
    JPanel southPanel = new JPanel();
        southPanel.setLayout(new FlowLayout());

    JPanel alignmentPanel = new JPanel();
    alignmentPanel.setBorder(
                new javax.swing.border.TitledBorder("Horizontal Alignment"));
    alignmentPanel.add(rButton1 = new JRadioButton("Left"));
    alignmentPanel.add(rButton2 = new JRadioButton("Center"));
    alignmentPanel.add(rButton3 = new JRadioButton("Right"));

    ButtonGroup buttonGroup = new ButtonGroup();
    buttonGroup.add(rButton1);
    buttonGroup.add(rButton2);
    buttonGroup.add(rButton3);

    JPanel columnPanel = new JPanel();
    columnPanel.setBorder(new javax.swing.border.EtchedBorder());
    columnPanel.setLayout(new FlowLayout());
    columnPanel.add(label2 = new JLabel("Column Size"));
    columnPanel.add(textField2 = new JTextField(10));

    southPanel.add(alignmentPanel);
    southPanel.add(columnPanel);
    getContentPane().add(southPanel, BorderLayout.SOUTH);

    textField1.addActionListener(this);
    rButton1.addActionListener(this);
    rButton2.addActionListener(this);
    rButton3.addActionListener(this);        
}

public void actionPerformed(ActionEvent e)
{
    if (e.getSource() == textField1)
    {
        textField1.setColumns(5);
    }
    else if (e.getSource() == rButton1)
            textField1.setHorizontalAlignment(textField1.LEFT);
    else if (e.getSource() == rButton2)
            textField1.setHorizontalAlignment(textField1.CENTER);
    else if (e.getSource() == rButton3)
            textField1.setHorizontalAlignment(textField1.RIGHT);
 }

Answer 1

它的工作，你只需要强制容器重新布局它的组件。这可以通过调用 revalidate 来实现。然后发出 repaint 请求(以移除任何视觉伪像)。