从 SwingWorker 线程返回数组到主线程

Question

I have a Swing GUI that when it open it performs aa thread in the background. For that I used SwingWorker thread. the problem is that I have an Array of String declare in main thread that is expected to collect information from swing worker thread and return that but after the thread is finishes the array is still empty. I guess once the thread is finished the array looses its values even though the array is declare in the main thread.

How can I return the values of the array to the main thread?

ArrayList<String> allnets = new ArrayList();
new SwingWorker<Object, Void>() {           
    @Override
    public Object doInBackground() throws SocketException, UnknownHostException {
        System.out.println("interfaces");
        netAdapter = new NetInterface();
        System.out.println(Thread.currentThread().getName());
        for(int i = 0; i < allnets.length; i++) {
            allnets.add("interface number");
        }
        return null;
    }

    @Override
    public void done() {                

    }   
}.execute();
System.out.println(Thread.currentThread().getName());
//      String[] inetfaces = {"eth0", "eth1", "wlan1", "wlan2", "wlan3"};
JComboBox comboBox = new JComboBox(allnets);
comboBox.setToolTipText("Interfaces");
comboBox.setBounds(444, 51, 137, 22);
frame.getContentPane().add(comboBox); 

Answer 1

To get the list of all interface names, call [static] method getNetworkInterfaces() of class java.net.NetworkInterface . And I assume you want to call that method from inside a SwingWorker . Also, from the code you posted, I assume you want to populate the JComboBox in the done() method of class SwingWorker . And since all the work is being done in the SwingWorker class, method doInBackground() doesn't need to return anything.

When it comes to using SwingWorker , I prefer to make a completely separate class that extends SwingWorker and not an anonymous inner class.

Here is the code for a Swing application. The JFrame displays a JLabel and a JComboBox . The JcomboBox contains the list of the names of all the network interfaces.

Note that on my Windows 10 (64 bit) machine running JDK 13, populating the JComboBox takes hardly any time at all, so the SwingWorker is not really needed. I guess you just want to practice using SwingWorker , correct?

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.net.NetworkInterface;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;

import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingWorker;
import javax.swing.WindowConstants;

public class SwngWrkr implements Runnable {
    private JComboBox<Object> combo;
    private JFrame frame;

    public void run() {
        showGui();
    }

    private JPanel createMainPanel() {
        JPanel mainPanel = new JPanel();
        mainPanel.add(new JLabel("Interfaces"));
        DefaultComboBoxModel<Object> model = new DefaultComboBoxModel<Object>();
        model.addElement("Loading...");
        combo = new JComboBox<Object>(model);
        mainPanel.add(combo);
        return mainPanel;
    }

    private void showGui() {
        frame = new JFrame("SW");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.add(createMainPanel(), BorderLayout.CENTER);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        new GetIfTsk(combo).execute();
    }

    public static void main(String[] args) {
        SwngWrkr instance = new SwngWrkr();
        EventQueue.invokeLater(instance);
    }
}

class GetIfTsk extends SwingWorker<Void, Void> {
    private JComboBox<Object> combo;
    private List<Object> netIfNames;

    public GetIfTsk(JComboBox<Object> combo) {
        this.combo = combo;
        netIfNames = new ArrayList<>();
    }

    protected Void doInBackground() throws Exception {
        Enumeration<NetworkInterface> ifs = NetworkInterface.getNetworkInterfaces();
        int ndx = 0;
        while (ifs.hasMoreElements()) {
            NetworkInterface ni = ifs.nextElement();
            String name = ni.getName();
            System.out.printf("%2d. %s%n", ++ndx, name);
            netIfNames.add(name);
        }
        return null;
    }

    protected void done() {
        DefaultComboBoxModel<Object> model = (DefaultComboBoxModel<Object>) combo.getModel();
        model.removeAllElements();
        model.addAll(netIfNames);
        model.setSelectedItem(netIfNames.get(0));
    }
}