Switching panels with MenuBar

Question

I have written some code which is designed to create a table and display the clipboard data (which will be copied from excel) in that table.

So i have one menu item in the menu bar "Import from Excel", which when clicked will take whatever excel data is in the clipboard and display a table in the panel below.

Also, I've written it so that the panel (in which the table is displayed) is capable of being switched depending on any future menu buttons which could lead to a completely different panel being displayed below.

So I have this DisplayExcelData class which implements a MainPage interface (which contains an init method). When the menu item is clicked, it fires an action event in the extended menubar class, which feeds the content pane the MainPage interface associated with that menu item (in this case DisplayExcelData is fed to the content pane when "Import from Excel is clicked), then init is called and it is added to the content pane.

When the program launches and nothing has been selected, it defaults to a InitialScreen class.

The DisplayExcelData class looks like this:

public class DisplayExcelData implements MainPageIF
{
    private ExcelTableModel tm = null;
    private Table table = new Table();
    private JPanel thisPanel = new Panel();

    public DisplayExcelData () 
    {
        super();
        thisPanel.setLayout(new BorderLayout());
    }

    @Override
    public void init()
    {
                //the test data I have been using is only 2 columns, so I'm just using
                //these as test columns at the moment
        tm = new ExcelTableModel("First, Second");
        table.setModel(tm);

        thisPanel.add(table, BorderLayout.CENTER);
    }

    @Override
    public JPanel getPanel()
    {
        return thisPanel;
    }
}

the ExcelTableModel takes the data in the clipboard and turns it into a TableModel

Then, in the contentPane, I have

public MainFrame()
{
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(50, 50, 800, 500);
    compInit();
}

private void compInit() 
{
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    contentPane.setLayout(new BorderLayout(0, 0));
    contentPane.setBackground(new Color(0,0,0));
    setContentPane(contentPane);

            //mf is the menu bar which is a class variable
    MenuBar menuBar = mf.getMenuBar();

    setPanelFromMenuBar();

    setMenuBar(menuBar);
}

private void setPanelFromMenuBar()
{
    MainPageIF page = mf.getPage();
    if (page == null)
    {
        page = new InitialScreen();
    }
    page.init();
            //mainPanel is a class variable
    mainPanel = page.getPanel();

    mainPanel.setVisible(true);
    contentPane.add(mainPanel, BorderLayout.CENTER);
}

@Override
public void actionPerformed(ActionEvent evt)
{
    Object source = evt.getSource();
    if (source instanceof MenuItem)
    {
        contentPane.removeAll();
        setPanelFromMenuBar();
        getContentPane().doLayout();
            update(getGraphics());
    }
}

If I change the code so I boot the program with the DisplayExcelData class as the initial screen, it works...it takes the excel data in the clipboard and displays it wonderfully in a table on the screen...if however, i insist that this table be displayed when i click on the MenuItem, it just displays a blank screen. When I debug, and check what mainPanel has in it...it contains the correct TableModel with the Excel data, contained in a JTable...but it wont display...I'm ripping my hair out as to why...

Can anyone help?

Answer 1

• I would not recommend extending JFrame class
• Use Anonymous inner class listeners instead of implementing ActionListener (unless the ActionListener must be accessible by other classes)

As for your actual problem:

Try calling revalidate() and repaint() on your JFrame instance after removing components and adding the new component:

 contentPane.removeAll();//remove
 setPanelFromMenuBar();//add

 revalidate();//refresh ui and layout
 repaint();

Or alternatively have a look at the CardLayout which allows flipping between JComponents like JPanels via CardLayout#show(...)