我第一次使用属性更改侦听器，所以我对它在几个类之间的使用方式不太熟悉。
我在java中编写了一个下载管理器，在类下载有downloadSize和sizeOfFile等字段。还有类DownloadPanel，它是一个GUI，是一个jpanel，包含一个JProgressbar和几个JLabel来显示文件的数量。下载或文件大小（使用下载字段）
Download类扩展了SwingWorker并使用HttpURLConnection从特定URL下载给定文件
在下载文件以更新其下载面板时，我已经实现了属性更改侦听器。问题是JProgressbar正在正确更新，但JLabel显示的downloadsSize和sizeOfFile不会通过下载文件来改变。
请注意，类中不相关的部分和getter / setter被省略，只包含与问题相关的部分。
Property Change Listener的实现：
public class DownloadPanelPropertyListener implements PropertyChangeListener {
Download download;
public DownloadPanelPropertyListener(Download download) {
this.download = download;
}
@Override
public void propertyChange(PropertyChangeEvent evt) {
if ("progress".equals(evt.getPropertyName()))
download.getDownloadPanel().getJpb().setValue((Integer) evt.getNewValue());
else if ("downloadPanel".equals(evt.getPropertyName())) {
DownloadPanel temp = (DownloadPanel) evt.getNewValue();
int ds = temp.download.getDownloadedSize();
int sof = temp.download.getSizeOfFile();
download.getDownloadPanel().setDownloadedSizeLabel(ds, sof);
}
}
DownloadPanel类代码：
public class DownloadPanel extends JPanel {
Download download;
JProgressBar jpb = new JProgressBar(0,100);
JLabel downloadSpeedLabel;
JLabel downloadedSizeLabel;
public DownloadPanel (Download d) {
download = d;
this.addPropertyChangeListener("downloadPanel",new DownloadPanelPropertyListener(download));
jpb.setValue( (int) (( (double) download.getDownloadedSize() / (double) download.getSizeOfFile()) * 100)) ;
jpb.setBounds(100,25,400,10);
jpb.setIndeterminate(false);
JLabel progressBarValue = new JLabel("%" + jpb.getValue() + "");
progressBarValue.setBounds(510,18,25,20);
add(progressBarValue);
downloadSpeedLabel = new JLabel (String.format ("%dKbs",download.getDownloadSpeed()));
downloadedSizeLabel = new JLabel (String.format ("%d MG / %d MG",download.getDownloadedSize(),download.getSizeOfFile()));
add(downloadSpeedLabel); add(downloadedSizeLabel);
}
和课程下载：
public class Download extends SwingWorker<Void,Void> implements Serializable,Runnable {
private transient DownloadPanel downloadPanel = null;
private transient MainPage mp;
private String fileName;
private String hostName;
private int downloadSpeed;
private int downloadedSize;
private int sizeOfFile;
private int queueIndex;
private URL url;
public Download (MainPage c,URL url,File f,int index) {
addPropertyChangeListener(new DownloadPanelPropertyListener(this));
mp = c;
this.url = url;
queueIndex = index;
downloadTime = time;
fileName = url.getFile();
hostName = url.getHost();
sizeOfFile = -1;
downloadSpeed = 0;
downloadedSize = 0;
}
public Void doInBackground () {
RandomAccessFile file = null;
InputStream stream = null;
try {
// Open connection to URL.
HttpURLConnection connection =
(HttpURLConnection) url.openConnection();
// Specify what portion of file to download.
connection.setRequestProperty("Range",
"bytes=" + downloadedSize + "-");
// Connect to server.
connection.connect();
// Make sure response code is in the 200 range.
if (connection.getResponseCode() / 100 != 2) {
System.out.println("0");
}
// Check for valid content length.
int contentLength = connection.getContentLength();
if (contentLength < 1) {
System.out.println("1");
}
/* Set the size for this download if it
hasn't been already set. */
if (sizeOfFile == -1) {
sizeOfFile = contentLength;
}
// Open file and seek to the end of it.
file = new RandomAccessFile(new File(s.getCurrentDirectory(),getFileName(url)),
"rw");
file.seek(downloadedSize);
stream = connection.getInputStream();
while (status == CURRENT) {
/* Size buffer according to how much of the
file is left to download. */
byte buffer[];
if (sizeOfFile - downloadedSize > MAX_BUFFER_SIZE) {
buffer = new byte[MAX_BUFFER_SIZE];
} else {
buffer = new byte[sizeOfFile - downloadedSize];
}
// Read from server into buffer.
int read = stream.read(buffer);
if (read == -1)
break;
// Write buffer to file.
file.write(buffer, 0, read);
downloadedSize += read;
setProgress ( (int) (( (double) getDownloadedSize() / (double) getSizeOfFile()) * 100));
}
/* Change status to complete if this point was
reached because downloading has finished. */
if (status == CURRENT) {
status = COMPLETE;
}
} catch (Exception e) {
System.out.println("2");
e.printStackTrace();
} finally {
// Close file.
if (file != null) {
try {
file.close();
} catch (Exception e) {}
}
// Close connection to server.
if (stream != null) {
try {
stream.close();
} catch (Exception e) {}
}
}
return null;
}
private String getFileName(URL url) {
String fileName = url.getFile();
return fileName.substring(fileName.lastIndexOf('/') + 1);
}
答案 0 :(得分：2)
我没有看到你在你的财产变更监听器中设置了JLabel的文本，但是说过，你不应该这样做，因为它违反了OOP封装。更确切地说：
DownloadPanel课程提供public void setPercentDownload(int value)方法，并在此方法中，通过setText(...) 和 JLabel的文字LI>
get()，以便捕获后台线程中可能发生的任何异常。null布局和setBounds。它们使得僵硬的GUI不能在所有平台上运行，并且是一个可以调试和增强的熊。使用布局管理器。例如，我的Minimal, Complete, and Verifiable example（MCVE）：
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.beans.*;
import java.io.Serializable;
import java.util.concurrent.ExecutionException;
import javax.swing.*;
public class FooProgress {
private static void createAndShowGui() {
JFrame frame = new JFrame("FooProgress");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new DownloadPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}
class DownloadListener implements PropertyChangeListener {
private DownloadPanel downloadPanel;
public DownloadListener(DownloadPanel downloadPanel) {
this.downloadPanel = downloadPanel;
}
@Override
public void propertyChange(PropertyChangeEvent evt) {
if ("progress".equals(evt.getPropertyName())) {
int value = (int) evt.getNewValue();
downloadPanel.setPercentDownload(value);
} else if ("state".equals(evt.getPropertyName())) {
if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
Download download = (Download) evt.getSource();
try {
download.get();
} catch (InterruptedException | ExecutionException e) {
// TODO: handle exceptions here
e.printStackTrace();
}
}
}
}
}
@SuppressWarnings("serial")
class DownloadPanel extends JPanel {
private static final String PROGRESS_FORMAT = "%03d%%";
private JProgressBar jpb = new JProgressBar(0, 100);
private JLabel downloadedSizeLabel = new JLabel(String.format(PROGRESS_FORMAT, 0));
private DownLoadAction downLoadAction = new DownLoadAction();
public DownloadPanel() {
JPanel topPanel = new JPanel();
topPanel.add(new JLabel("Download Progress:"));
topPanel.add(downloadedSizeLabel);
JPanel bottomPanel = new JPanel();
bottomPanel.add(new JButton(downLoadAction));
setLayout(new BorderLayout());
add(topPanel, BorderLayout.PAGE_START);
add(jpb);
add(bottomPanel, BorderLayout.PAGE_END);
}
public void setPercentDownload(int value) {
downloadedSizeLabel.setText(String.format(PROGRESS_FORMAT, value));
jpb.setValue(value);
if (value == 100) {
downLoadAction.setEnabled(true);
}
}
private class DownLoadAction extends AbstractAction {
public DownLoadAction() {
super("Download");
putValue(MNEMONIC_KEY, KeyEvent.VK_D);
}
@Override
public void actionPerformed(ActionEvent e) {
setEnabled(false);
setPercentDownload(0);
Download download = new Download();
DownloadListener listener = new DownloadListener(DownloadPanel.this);
download.addPropertyChangeListener(listener);
download.execute();
}
}
}
class Download extends SwingWorker<Void, Void> implements Serializable, Runnable {
private static final long SLEEP_TIME = 200;
public Void doInBackground() throws Exception {
int myProgress = 0;
while (myProgress < 100) {
myProgress += (int) (10 * Math.random());
myProgress = Math.min(myProgress, 100);
setProgress(myProgress);
Thread.sleep(SLEEP_TIME);
}
return null;
}
}
将来，您希望使用您的代码创建和发布MCVE，以便我们可以毫不费力地编译，运行和测试它。你的代码中有太多的文件处理，我们目前无法测试。我已经用90％的代码替换了Thread.sleep。