Question

I’m having trouble with a contentPane. Here’s the code in question:

public void graph() {
    JFrame frame = new JFrame("Graph");
    Graph[] graphs = new Graph[timeSlices];
    int k = 0;

    for (TreeMap<MyPoint, BigDecimal> prevU : prevUs) {
        graphs[k] = new Graph(prevU);
        k++;
    }

    // The KeyList handles switching between graphs.
    frame.addKeyListener(new KeyList(frame.getContentPane(), graphs));

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(810, 500);
    frame.setVisible(true);
}

private class KeyList extends KeyAdapter {
    private Container contentPane;
    private Graph[] graphs;
    private int index;

    public KeyList(Container contentPane, Graph[] graphs) {
        this.contentPane = contentPane;
        this.graphs = graphs;
        this.index = 0;

        this.contentPane.add(this.graphs[0]);
    }

    public void keyPressed(KeyEvent e) {
        // Go back a time step
        if (e.getKeyCode() == KeyEvent.VK_LEFT && index > 0) {
            contentPane.remove(graphs[index]);
            contentPane.add(graphs[--index]);
            contentPane.validate();
            System.out.println(index);
        }
        // Go forward a time step
        else if (e.getKeyCode() == KeyEvent.VK_RIGHT && index < timeSlices - 1) {
            contentPane.remove(graphs[index]);
            contentPane.add(graphs[++index]);
            contentPane.validate();
            System.out.println(index);
        }
        // Exit if Esc is hit
        else if (e.getKeyCode() == KeyEvent.VK_ESCAPE)
            System.exit(0);
    }
}

Graph is just a Component, easy peasy. When I hit the right arrow, I want to replace the currently displayed Graph with the next one in the array, and when I hit the left arrow, I want to replace the Graph with the previous one in the array.

The weird thing is that when I hit right, it works just fine. However, when I hit left, the Graph doesn’t change. The index changes, thus I know the code is being reached, but the GUI doesn’t change.

Now get ready for this. When I comment out the right key’s validate line, the left one will work about half the time. What is going on there? Here’s the rest of the code if you want to run and see for your self (just one file) : http://pastebin.com/qWxWrypK. The starting paramemters I’m currently using are T=1, dt=.01, L=1, h=.05.

I was looking into it, I thought it might be because the contentPane of a JFrame is really a JPanel, but that line of thinking didn’t get anywhere…

Thanks for any help

Edit:

So I’m still working with it. Here’s another weird thing. If I set the index in the KeyList class to timeSlices-1 (basically getting the last Graph in graphs array), and I hit left, it works! But, now the right doesn’t! Something weird has to be going on with the array or something because the index changes just fine. Hmm.

Edit:

Something’s going on with the array. For some reason, the Graph can only be used once. Perhaps it’s being destroyed on removal? Or something like that…

Answer 1

Instead of trying to remove/add panels to a container use a CardLayout which was designed for this purpose.

Also, don’t use KeyListeners. Instead you should be using Key Bindings. Then you simply bind the next/previous keys to the next/previous methods of the card layout.