java - JFileChooser 不将文件名返回到主方法

Question

我对 Swing 和 AWT 还很陌生。虽然我有Java开发经验。我正在尝试使用 JFileChooser 读取文件并获取主方法中的内容。所有 Swing 和 AWT 的大师请帮助我确定我缺少什么。

这是我的代码:

package com.ui;

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;

public class HomeScreen extends JFrame
{
    private static final long serialVersionUID = -7604272718213756686L;

    String fileContent;
    final JFileChooser fc = new JFileChooser();
    public HomeScreen()
    {
        super("Home Screen");
        setLayout(new FlowLayout());
        setSize(500,500);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setResizable(false);

        // Button to open file
        final JButton button = new JButton("Select File");
        button.addActionListener
        (
            new ActionListener()
            {
                public void actionPerformed(ActionEvent e)
                {
                    int ret = fc.showDialog(button.getParent(), "Open");
                    if(ret == JFileChooser.APPROVE_OPTION)
                    {
                        File f = fc.getSelectedFile();
                         BufferedReader br;
                        try {
                            br = new BufferedReader(new FileReader(f));
                            String st ="";
                            StringBuilder sb = new StringBuilder();
                            while((st=br.readLine())!=null)
                            {
                                sb.append(st);
                            }
                            fileContent = sb.toString();

                        } catch (FileNotFoundException e1) {
                            // TODO Auto-generated catch block
                            e1.printStackTrace();
                        } catch (IOException e1) {
                            // TODO Auto-generated catch block
                            e1.printStackTrace();
                        }
                    }
                }
            }
        );

        System.out.println(fc.getSelectedFile()+" _____________________");
        add(button);
    }
    public static void main(String[] args)
    {
        HomeScreen screen = new HomeScreen();
    }
}

即使我选择了包含大量内容的文件，也会打印 null___________________________。

Answer 1

您的System.out.println()语句不在适当的代码块中。您将其放入 UI 初始化方法(这里是构造函数)中，而不是放在 actionPerformed 方法中。

现在，还有一些额外的事情需要考虑:

• 所有与 Swing 相关的操作都必须在 EDT 中完成(例如使用 SwingUtilities.invokeLater)
• JFrame.setVisible(true) 应该是 UI 初始化代码的最后一个语句
• 如果加载大文件，则应考虑将文件的加载移至 EDT(事件调度线程)以外的另一个线程，以避免 GUI 卡住(SwingWorker 通常对此很有帮助) )

这是代码的更新版本(我添加了一个文本区域来显示加载的内容):

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class HomeScreen extends JFrame {
    private static final long serialVersionUID = -7604272718213756686L;

    String fileContent;
    final JFileChooser fc = new JFileChooser();

    private JTextArea textArea;

    public HomeScreen() {
        super("Home Screen");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setResizable(false);

        // Button to open file
        final JButton button = new JButton("Select File");
        button.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                int ret = fc.showDialog(button.getParent(), "Open");
                if (ret == JFileChooser.APPROVE_OPTION) {
                    File f = fc.getSelectedFile();
                    System.out.println(fc.getSelectedFile() + " _____________________");
                    BufferedReader br;
                    try {
                        br = new BufferedReader(new FileReader(f));
                        String st = "";
                        StringBuilder sb = new StringBuilder();
                        while ((st = br.readLine()) != null) {
                            sb.append(st);
                        }
                        fileContent = sb.toString();
                        textArea.setText(fileContent);
                    } catch (FileNotFoundException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    } catch (IOException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    }

                }
            }
        });
        textArea = new JTextArea(24, 40);
        textArea.setLineWrap(true);
        textArea.setEditable(false);
        add(new JScrollPane(textArea));
        add(button, BorderLayout.SOUTH);
        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                HomeScreen screen = new HomeScreen();
            }
        });

    }
}