java - 显示图像

Question

我想通过单击按钮将来自 Web 的图像显示到另一个 JFrame 中的面板。每当我单击按钮时，首先加载图像；在此期间，当前表单可能会卡住。加载图像后，表单将与图像一起显示。我怎样才能避免我的表格卡住的情况，因为它非常烦人。在我的代码中:

我现在的类(class):

private void btn_TrackbusActionPerformed(java.awt.event.ActionEvent evt) {                                             
        try {
            sendMessage("Query,map,$,start,211,Arsenal,!");
            System.out.println(receiveMessage());
        } catch (UnknownHostException ex) {
            Logger.getLogger(client_Trackbus.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(client_Trackbus.class.getName()).log(Level.SEVERE, null, ex);
        }
        catch (Exception ex) {
            Logger.getLogger(client_Trackbus.class.getName()).log(Level.SEVERE, null, ex);
        }
        client_trackedbus nextform=new client_trackedbus(planform,connection,packet_receive,packet_send);
        this.setVisible(false);
        this.dispose();
        nextform.setVisible(true);
        // TODO add your handling code here:
    }                                            

我的下一个显示图像的类:

public class client_trackedbus extends javax.swing.JFrame {
    client_planform planform=null;
    DatagramSocket connection=null;
    DatagramPacket packet_receive=null;
    DatagramPacket packet_send=null;
    JLabel label=null;
    /** Creates new form client_trackedbus */
    public client_trackedbus(client_planform planform,DatagramSocket connection,DatagramPacket packet_receive,DatagramPacket packet_send) {
        initComponents();
        this.planform=planform;
        this.connection=connection;
        this.packet_receive=packet_receive;
        this.packet_send=packet_send;
        try {
            displayMap("http://www.huddletogether.com/projects/lightbox2/images/image-2.jpg", jPanel1, new JLabel());
        } catch (MalformedURLException ex) {
            Logger.getLogger(client_trackedbus.class.getName()).log(Level.SEVERE, null, ex);
        }

    }


    private void displayMap(String url,JPanel panel,JLabel label) throws MalformedURLException{
        URL imageurl=new URL(url);
        Image image=(Toolkit.getDefaultToolkit().createImage(imageurl));
        ImageIcon icon = new ImageIcon(image);
        label.setIcon(icon);
        panel.add(label);
       // System.out.println(panel.getSize().width);
        this.getContentPane().add(panel);
    }


    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();
        btn_Exit = new javax.swing.JButton();
        btn_Plan = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Public Transport Journey Planner");

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 368, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 172, Short.MAX_VALUE)
        );

        jLabel1.setFont(new java.awt.Font("Arial", 1, 18));
        jLabel1.setText("Your tracked bus");

        btn_Exit.setText("Exit");
        btn_Exit.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn_ExitActionPerformed(evt);
            }
        });

        btn_Plan.setText("Plan journey");
        btn_Plan.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn_PlanActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(104, 104, 104)
                        .addComponent(jLabel1))
                    .addGroup(layout.createSequentialGroup()
                        .addContainerGap()
                        .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(65, 65, 65)
                        .addComponent(btn_Plan)
                        .addGap(65, 65, 65)
                        .addComponent(btn_Exit, javax.swing.GroupLayout.PREFERRED_SIZE, 87, javax.swing.GroupLayout.PREFERRED_SIZE)))
                .addContainerGap(20, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(35, 35, 35)
                .addComponent(jLabel1)
                .addGap(18, 18, 18)
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(btn_Exit)
                    .addComponent(btn_Plan))
                .addContainerGap(12, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        

    private void btn_ExitActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        Exitform();
    }                                        

    private void btn_PlanActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        this.setVisible(false);
        this.dispose();
         this.planform.setVisible(true);
    }                                        


    private void Exitform(){
        this.setVisible(false);
        this.dispose();

    }
    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
               // new client_trackedbus().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btn_Exit;
    private javax.swing.JButton btn_Plan;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JPanel jPanel1;
    // End of variables declaration                   

}

Answer 1

如文章 Concurrency in Swing 中所建议，您的按钮处理程序的查询可能会阻塞事件调度线程。使用javax.swing.SwingWorker是一种在后台加载图像，同时显示进度并保持 GUI 线程 Activity 的方法。

附录:这是一个 sscce加载 SO 标志；它已更新以处理异常并调整封闭容器的大小以适应加载的图像:

import java.awt.*;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.ExecutionException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.*;

/**
 * @see http://stackoverflow.com/questions/4530659
 */
public final class WorkerTest extends JFrame {

    private final JLabel label = new JLabel("Loading...");

    public WorkerTest() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        label.setHorizontalTextPosition(JLabel.CENTER);
        label.setVerticalTextPosition(JLabel.BOTTOM);
        this.add(label);
        this.pack();
        this.setLocationRelativeTo(null);
    }

    private void start() {
        new ImageWorker().execute();
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                WorkerTest wt = new WorkerTest();
                wt.setVisible(true);
                wt.start();
            }
        });
    }

    class ImageWorker extends SwingWorker<Image, Void> {

        private static final String TEST
            = "http://cdn.sstatic.net/stackexchange/img/logos/so/so-logo.png";

        @Override
        protected Image doInBackground() throws IOException {
            Image image = ImageIO.read(new URL(TEST));
            return image.getScaledInstance(640, -1, Image.SCALE_SMOOTH);
        }

        @Override
        protected void done() {
            try {
                ImageIcon icon = new ImageIcon(get());
                label.setIcon(icon);
                label.setText("Done");
                WorkerTest.this.pack();
                WorkerTest.this.setLocationRelativeTo(null);
            } catch (InterruptedException | ExecutionException e) {
                e.printStackTrace();
            }
        }
    }
}