BorderLayout不工作

Question

我无法让BorderLayout工作.我希望取消按钮位于底部,但它不起作用.码:

import java.awt.BorderLayout;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ButtonModel;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

class Test {
    public static JFrame owner;
    public static void main(String[] args) {
        final JDialog frame = new JDialog(owner, "Test");
        frame.setLayout(new BorderLayout());
        frame.setSize(500, 300);
        final JPanel panel = new JPanel();
        final ButtonGroup group = new ButtonGroup();
        String[] options = {"1", "2", "3"};
        for (String text : options) {
            JRadioButton option = new JRadioButton(text);
            option.setActionCommand(text);
            group.add(option);
            panel.add(option);
        }
        JButton okButton = new JButton("OK");
        okButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                ButtonModel selectedModel = group.getSelection();
                if (selectedModel != null) {
                    System.err.println(selectedModel.getActionCommand());
                }
            }
        });
        panel.add(okButton);
        JButton cancelButton = new JButton("Cancel");
        cancelButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                frame.setVisible(false);
                frame.dispose();
            }
        });
        panel.add(cancelButton, BorderLayout.SOUTH);
        frame.add(panel);
        frame.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        frame.setVisible(true);
    }
}

Answer 1

使用BorderLayout.SOUTH常量将cancelButton添加到面板:

  panel.add(cancelButton, BorderLayout.SOUTH);

但是在哪里将面板的布局设置为BorderLayout？由于您从未设置此容器的布局,因此它将使用JPanel的默认布局,即FlowLayout.

解决方案:将面板JPanel的布局设置为BorderLayout以获取BorderLayout行为.

一旦你解决了这个问题,你会遇到另一个问题:

  for (String text : options) {
     JRadioButton option = new JRadioButton(text);
     option.setActionCommand(text);
     group.add(option);
     panel.add(option);
  }

您将JRadioButton添加到同一面板JPanel而不考虑布局.我怀疑你想要将JRadioButtons添加到他们自己的JPanel,可能是一个使用GridLayout(1, 0)或GridLayout(0, 1)取决于所需的方向,然后你想将这个JPanel添加到面板,可能在BorderLayout.CENTER位置.

你的okButton也有类似的问题,因为你将它添加到面板而不考虑布局.

Answer 2

你可以尝试改变

panel.add(cancelButton, BorderLayout.SOUTH);

至

frame.add(cancelButton, BorderLayout.SOUTH);

结果: