java - 如何在运行时设置 JTextField 的宽度？

Question

有人可以帮我如何在运行时设置 JTextField 的宽度吗？我希望我的文本字段在运行时调整大小。它会询问用户的长度，然后输入会改变文本字段的宽度。

if(selectedComponent instanceof javax.swing.JTextField){
    javax.swing.JTextField txtField = (javax.swing.JTextField) selectedComponent;
    //txtField.setColumns(numInput); //tried this but it doesn't work
    //txtField.setPreferredSize(new Dimension(numInput, txtField.getHeight())); //also this
    //txtField.setBounds(txtField.getX(), txtField.getY(), numInput, txtField.getHeight()); 
    //and this
    txtField.revalidate();
}

我为此使用了 null 布局，因为我处于编辑模式。

Answer 1

您只需要使用 jTextFieldObject.setColumns(int columnSize) .这将使您可以在运行时增加它的大小。你最后不能这样做的原因是 null 布局。这是不鼓励使用 null Layout/Absolute Positioning 的主要原因之一。这是一个小例子，您可以亲自尝试一下:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class JTextFieldExample
{
    private JFrame frame;
    private JPanel contentPane;
    private JTextField tfield;
    private JButton button;
    private int size = 10;

    private ActionListener action = new ActionListener()
    {
        public void actionPerformed(ActionEvent ae)
        {
            String input = JOptionPane.showInputDialog(
                                frame, "Please Enter Columns : "
                                                , String.valueOf(++size));
            tfield.setColumns(Integer.parseInt(input));                 
            contentPane.revalidate();
            contentPane.repaint();
        }
    };

    private void createAndDisplayGUI()
    {
        frame = new JFrame("JTextField Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);           

        contentPane = new JPanel();
        contentPane.setLayout(new FlowLayout(FlowLayout.LEFT, 5, 5));

        tfield = new JTextField();
        tfield.setColumns(size); 

        JButton  button = new JButton("INC Size");
        button.addActionListener(action);

        contentPane.add(tfield);
        contentPane.add(button);

        frame.getContentPane().add(contentPane);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new JTextFieldExample().createAndDisplayGUI();
            }
        });
    }
}

对于绝对定位你需要调用setSize()在 JTextField 上以获得结果，但您应该始终牢记不鼓励使用此方法的原因，如 Java Doc's 中给出的那样第一段:

Although it is possible to do without a layout manager, you should use a layout manager if at all possible. A layout manager makes it easier to adjust to look-and-feel-dependent component appearances, to different font sizes, to a container's changing size, and to different locales. Layout managers also can be reused easily by other containers, as well as other programs.