Question

我正在尝试使用JFilechooser打开文本文件并将字符串放在JList中。我认为所有字符串都会进入列表但我不知道为什么字符串不会出现在JScrollPane上。 grouplayout有什么问题吗？我不知道该改变什么......

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.io.*;
import java.util.*;
import java.util.List; 

public class WordFinder extends JFrame implements ActionListener {

    private WordList words = new WordList();

    private JScrollPane scroll;
    private JLabel label;
    private JLabel word;
    private JTextField textArea;
    private JButton button;

    private JMenuBar menuBar;
    private JMenu menu;
    private JMenuItem menuItem, menuItem2;

    private JFileChooser fc;

    private JList list;


    static private final String newline = "\n";

    private int lineCount;



    public WordFinder() {
        super("Word Finder");

        fc = new JFileChooser();
        fc.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);

        menuBar = new JMenuBar();
        menu = new JMenu("File");
        menuBar.add(menu);

        menuItem = new JMenuItem("Open...");
        menuItem.addActionListener(this);

        menuItem2 = new JMenuItem("Exit");
        menuItem2.addActionListener(this);

        menu.add(menuItem);
        menu.add(menuItem2);
        setJMenuBar(menuBar);

        label = new JLabel("Find: ");

        word = new JLabel(lineCount + " words total");

        textArea = new JTextField();
        textArea.setEditable(true);
        textArea.setPreferredSize(new Dimension(200, 20));


        button = new JButton("Clear");
        button.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        textArea.setText("");
                    }
                });

        scroll = makeListView();
        scroll.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scroll.setPreferredSize(new Dimension(200, 230));

        GroupLayout layout = new GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setAutoCreateGaps(true);
        layout.setAutoCreateContainerGaps(true);

        layout.setHorizontalGroup(layout.createSequentialGroup()
                .addComponent(label)
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                        .addComponent(textArea)
                        .addComponent(word)
                        .addComponent(scroll))
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                        .addComponent(button)));

        layout.setVerticalGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                        .addComponent(label)
                        .addComponent(textArea)
                        .addComponent(button))
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                        .addComponent(word))
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING))
                        .addComponent(scroll));

        setVisible(true);
        pack();
        // call System.exit() when user closes the window
        setDefaultCloseOperation(EXIT_ON_CLOSE);

    }


    private JScrollPane makeListView() {
    //      String[] labels = {"1", "2", "3"};
    //      list = new JList(labels);

        JScrollPane listScroller = new JScrollPane(list);
        return listScroller;
    }

    private void updateListView(DefaultListModel listModel) {
        list = new JList(listModel);
        scroll = new JScrollPane(list);
    }

    public void actionPerformed(ActionEvent e) {

        DefaultListModel listModel = new DefaultListModel();

        if (e.getSource() == menuItem) {
            int returnVal = fc.showOpenDialog(WordFinder.this);

            if (returnVal == JFileChooser.APPROVE_OPTION) {
                File file = fc.getSelectedFile();
                String fileName = file.getAbsolutePath();

                try {
                    FileReader files = new FileReader(fileName);
                    BufferedReader br = new BufferedReader(files);

                    String str;                 
                    while((str = br.readLine()) != null) {
                        listModel.addElement(str);
                        //System.out.println(str);
                        lineCount++;
                    }
                    System.out.println(lineCount);

                    updateListView(listModel);
                    br.close();
                } catch (Exception ex) {
                    ex.printStackTrace(System.out);
                    System.out.println("can't read file");
                }

                System.out.println("Opening: " + file.getName() + newline);
            }
        } else if (e.getSource() == menuItem2) {
            setVisible(false);
            dispose();
        }
    }


    /**
     * Main method.  Makes and displays a WordFinder window.
     * @param args Command-line arguments.  Ignored.
     */
    public static void main(String[] args) {
        // In general, Swing objects should only be accessed from
        // the event-handling thread -- not from the main thread
        // or other threads you create yourself.  SwingUtilities.invokeLater()
        // is a standard idiom for switching to the event-handling thread.
        SwingUtilities.invokeLater(new Runnable() {
            public void run () {
                // Make and display the WordFinder window.
                new WordFinder();
            }
        });
    }    
}

Answer 1

当您致电makeListView时，JList为null因为尚未初始化...因此，您基本上是在说scroll = new JScrollPane(null); ...这不是特别有帮助......

接下来，当您致电updateListView时，您会创建JList和JScrollPane的新实例，并且不对它们执行任何操作......

private void updateListView(DefaultListModel listModel) {
    list = new JList(listModel);
    scroll = new JScrollPane(list);
}

因此它们永远不会显示在屏幕上......

要纠正此问题，您需要进行一些修改......

在创建JList

list

JScrollPane

而不是创建list和scroll的新实例，只需使用JList#setModel

您可能还想查看Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?

使用JList，您可以通过使用JList#setVisibleRowCount和JList#setPrototypeCellValue

JScrollPane

JList没有显示在JScrollPane上

1 个答案: