java - JProgressBar 无法从 ActionEvent 正确显示

Question

在下面的代码中，当从 main() 中调用 doSomething() 时，JProgressBar 会正确显示，但当作为ActionEvent 的结果 - 界面似乎卡住了。有什么问题？

import java.awt.BorderLayout; 

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


public class ThreadedDialog  extends JFrame implements ActionListener{                
    private JDialog dlg;
    private JButton button;

    private void buildInterface(){
        button = new JButton("do stuff;");
        button.addActionListener(this);
        this.getContentPane().setLayout(new BorderLayout()); 
        this.getContentPane().add(BorderLayout.CENTER, button); 


        dlg = new JDialog(this, "Progress Dialog", true); 
        JProgressBar dpb = new JProgressBar(0, 500); 
        dlg.getContentPane().setLayout(new BorderLayout()); 
        dlg.getContentPane().add(BorderLayout.CENTER, dpb); 
        dlg.getContentPane().add(BorderLayout.NORTH, new JLabel("Progress..."));         
        dlg.setDefaultCloseOperation(JDialog.DO_NOTHING_ON_CLOSE); 
        dlg.setSize(300, 75); 
        dlg.setLocationRelativeTo(this);
        dpb.setIndeterminate(true);        
    }

    public void doSomething(){
        Thread t = new Thread(new Runnable(){ 
            public void run() { 
                dlg.show(); 
            } 
        });                          
        t.start();     
        try { 
            for (int i=0; i<100; i++){
                System.out.println("wtf is going on here?");
                Thread.sleep(5000);
            }
        } catch (InterruptedException e) { 
            e.printStackTrace(); 
        }
        dlg.hide();         
    }

    public static void main(String[] args) { 
        ThreadedDialog me = new ThreadedDialog();

        me.buildInterface();        
        me.pack();
        me.setVisible(true);
        me.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        //me.doSomething();
    }

    public void actionPerformed(ActionEvent event) {
        doSomething();
    }
} 

谢谢

Answer 1

您对 Swing 组件所做的一切都应该在事件分派(dispatch)线程 (EDT) 上完成(即 Swing 用来调用您的事件的线程)。您应该启动线程以执行冗长的后台操作。

在您的代码中，您执行相反的操作:您尝试在另一个线程中显示对话框，并在 EDT 中执行长操作。

这是固定代码:

package fr.free.jnizet.stackoverflow;

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

import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JProgressBar;
import javax.swing.SwingUtilities;


public class ThreadedDialog  extends JFrame implements ActionListener{
    private JDialog dlg;
    private JButton button;

    private void buildInterface(){
        button = new JButton("do stuff;");
        button.addActionListener(this);
        this.getContentPane().setLayout(new BorderLayout());
        this.getContentPane().add(BorderLayout.CENTER, button);


        dlg = new JDialog(this, "Progress Dialog", true);
        JProgressBar dpb = new JProgressBar(0, 500);
        dlg.getContentPane().setLayout(new BorderLayout());
        dlg.getContentPane().add(BorderLayout.CENTER, dpb);
        dlg.getContentPane().add(BorderLayout.NORTH, new JLabel("Progress..."));
        dlg.setDefaultCloseOperation(JDialog.DO_NOTHING_ON_CLOSE);
        dlg.setSize(300, 75);
        dlg.setLocationRelativeTo(this);
        dpb.setIndeterminate(true);
    }

    public void doSomething(){
        // create a thread for the background task
        Thread t = new Thread(new Runnable(){
            public void run() {
                try {
                    for (int i=0; i<100; i++){
                        System.out.println("wtf is going on here?");
                        Thread.sleep(5000);
                    }
                }
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
                // when the background task is finished, hide the dialog in the EDT.
                SwingUtilities.invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        dlg.setVisible(false);
                    }

                });
            }
        });
        t.start();

        // show the dialog in the EDT
        dlg.setVisible(true);
    }

    public static void main(String[] args) {
        // create the GUI in the EDT
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                ThreadedDialog me = new ThreadedDialog();

                me.buildInterface();
                me.pack();
                me.setVisible(true);
                me.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            }
        });

    }

    public void actionPerformed(ActionEvent event) {
        doSomething();
    }
}

你应该阅读 this tutorial ，并学习使用 SwingWorker 执行后台任务。