Question

When I press the button in the program below I want the popup menu from the JComboBox to appear and remain up.

However it only does that when on the second push when the Combobox is already visible. Is there any way I can make it appear on the first push?

public class Problem extends JPanel 
implements ActionListener{

private static String SEARCH = "start search";
private static String SELECTED = "Selected";

private JTextField field2;
private JTextField field1;

private JComboBox list = new JComboBox();

public Problem() {
    super(new GridBagLayout());

    //Construct the panel
    field2=new JTextField("");
    field1=new JTextField("7564");
    JButton search=new JButton("Search");
    search.addActionListener(this);
    search.setActionCommand(SEARCH);

    list.addActionListener(this);
    list.setActionCommand(SELECTED);


    //Add everything to this panel.
    GridBagConstraints c = new GridBagConstraints();

    c.gridx = 0;
    c.gridy = 0;
    c.gridwidth = 8;
    c.gridheight = 3;
    c.fill = GridBagConstraints.BOTH;
    c.weightx = 1;
    c.weighty = 0;
    c.anchor = GridBagConstraints.NORTH;

    add(field2,c);

    list.setVisible(false);
    add(list,c);

    c.gridx = 8;
    c.gridy = 0;
    c.gridwidth = 8;
    c.gridheight = 3;
    c.fill = GridBagConstraints.BOTH;
    c.weightx = 1;
    c.weighty = 0;
    c.anchor = GridBagConstraints.NORTH;

    add(field1,c);

    c.gridx = 16;
    c.gridy = 0;
    c.gridwidth = 4;
    c.gridheight = 3;
    c.fill = GridBagConstraints.BOTH;
    c.weightx = 1;
    c.weighty = 0;
    c.anchor = GridBagConstraints.NORTH;

    add(search,c);


}

public void actionPerformed(ActionEvent ae) {



    if (ae.getActionCommand()==SEARCH){
        String f2=field2.getText();
        String f1=field1.getText();
        if(f2.equals("")){

            f2=selection(f1);
            f2=null;
        }
        if(f2!=null){
            field2.setText(f2);
        }
        else{
            System.out.println("setPopupVisible runs");
            field2.setVisible(false);
            list.setVisible(true);
            field2.setText("");
            list.setPopupVisible(true);
        }
    }
    else if(ae.getActionCommand().equals(SELECTED)){
        System.out.println("select");
        String listtext=(String) list.getSelectedItem();
        list.removeAllItems();
        if(listtext==null||!listtext.contains(": ")){
            return;
        }
        String f2=listtext.split(": ")[0];
        list.setVisible(false);
        field2.setVisible(true);
        field2.setText(f2);
    }
}

private String selection(String sn) {
    System.out.println("selection runs");

    String name="7";
    list.removeActionListener(this);
    list.removeAllItems();
        list.addItem(name);
    list.addActionListener(this);
    return null;
}

private static void createAndShowGUI() {
    //Create and set up the window.
    JFrame frame = new JFrame("Stuff");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    Problem newContentPane = new Problem();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    frame.pack();
    frame.setVisible(true);
    frame.setSize(800, 600);
}

public static void main(String[] args) throws FileNotFoundException {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            createAndShowGUI();
        }
    });
}
}

Answer 1

When toggling visibility of components, make sure the component has completed its internal update before doing custom stuff, that is f.i. delay the call to showing a combo’s popup relative to showing the combo itself:

            list.setVisible(true);
            SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    list.setPopupVisible(true);
                }
            });