Jframe中未显示两个Jpanel

Question

I don't understand why mediaPanel and selectedMediaPanel are not shown in the JFrame . What is the reason?

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Arrays;
import java.util.List;
import java.util.Vector;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListSelectionModel;


public class MediaSelectionGUI {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        new MediaSelectionGUI();

    }

    public MediaSelectionGUI(){

        final Situation situation = new Situation();

        JFrame guiFrame = new JFrame();

        //make sure the program exits when the frame closes
        guiFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        guiFrame.setTitle("Communications Support Tool version 0.1");
        guiFrame.setSize(1000,500);
        guiFrame.setLayout(new FlowLayout());


      //This will center the JFrame in the middle of the screen
        guiFrame.setLocationRelativeTo(null);

        Vector<Media> media_option = new Vector<Media>(Arrays.asList(new Media[]{Media.Chat,Media.E_mail,Media.Intranet,Media.Meeting,Media.Social_Media, Media.Telefon, Media.Video}));
        Vector<Media> selected_media_option = new Vector<Media>();

        Zweck[] zweck_option = {Zweck.Anweisung, Zweck.Austausch, Zweck.Informieren, Zweck.Koordination};
        Ort[] ort_option = {Ort.Gleicher_Ort, Ort.Unterschiedlicher_Ort, Ort.Andere_Zeitzone};
        Anzahl[] anzahl_option = {Anzahl.Zwei_Personen, Anzahl.Klein_Gruppe, Anzahl.Publikum};

      //Create the second JPanel. Add a JLabel and JList and
        final JPanel mediaPanel = new JPanel(null);
        JLabel mediaLabel = new JLabel("All Media:");
        final JList<Media> media = new JList<Media>(media_option);
        media.setLayoutOrientation(JList.HORIZONTAL_WRAP);
        media.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);

        mediaPanel.add(mediaLabel);
        mediaPanel.add(media);
        mediaPanel.setVisible(true);

        final JPanel selectedMediaPanel = new JPanel(null);
        JLabel selectedmediaLabel = new JLabel("Selected Media:");
        final JList<Media> selected_media = new JList<Media>(selected_media_option);
        selected_media.setLayoutOrientation(JList.HORIZONTAL_WRAP);
        selected_media.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);

        selectedMediaPanel.add(selectedmediaLabel);
        selectedMediaPanel.add(selected_media);
        selectedMediaPanel.setVisible(true);

        JButton select_button = new JButton("select");
        JButton deselect_button = new JButton("deselect");

        select_button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                // TODO Auto-generated method stub
                List<Media> selected_media_option = media.getSelectedValuesList();
                for (Media medium: selected_media_option){
                    selected_media.getSelectedValuesList().add(medium);
                }
            }
        });


        deselect_button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                // TODO Auto-generated method stub
                List<Media> selected_media_option = selected_media.getSelectedValuesList();
                for (Media medium: selected_media_option){
                    media.getSelectedValuesList().add(medium);
                }
            }
        });

        select_button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                // TODO Auto-generated method stub
                List<Media> selected_media_option = media.getSelectedValuesList();
                for (Media medium: selected_media_option){
                    situation.media_collection.add(medium);
                    System.out.println(medium);
                }
            }
        });


      // Zweck Panel
        final JPanel zweckPanel = new JPanel();
        JLabel zweckLabel = new JLabel("Zweck:");
        JComboBox<Zweck> zweck = new JComboBox<Zweck>(zweck_option);
        zweckPanel.add(zweckLabel);
        zweckPanel.add(zweck);

     // Ort Panel
        final JPanel ortPanel = new JPanel();
        JLabel ortLabel = new JLabel("Ort:");
        JComboBox<Ort> ort = new JComboBox<Ort>(ort_option);    
        ortPanel.add(ortLabel);
        ortPanel.add(ort);

     // Anzahl Panel
        final JPanel anzahlPanel = new JPanel();
        JLabel anzahlLabel = new JLabel("Anzahl:");
        JComboBox<Anzahl> anzahl = new JComboBox<Anzahl>(anzahl_option);
        ortPanel.add(anzahlLabel);
        ortPanel.add(anzahl);


        guiFrame.add(mediaPanel);
        guiFrame.add(select_button);
        guiFrame.add(deselect_button);
        guiFrame.add(selectedMediaPanel);
        guiFrame.add(zweckPanel);
        guiFrame.add(ortPanel);
        guiFrame.add(anzahlPanel);

        guiFrame.setVisible(true);
    }

}

Answer 1

The main reason your having problems is your adding two panels with null layouts to the frame that is using a layout manager.

The frames layout manager is checking these panels preferred sizes and they are returning 0x0. So you panels are showing, they've just be sized to 0x0

Try using appropriate layout managers for the panels as well

Answer 2

In the JPanel constructor, you are setting a null LayoutManager, then the components will be without size.

Just remove the null from JPanel constructor.