Question

I’m having more “I’m hopeless at programming” problems.

I have a piece of code which uses StringBuilder to display elements of an array in a text panel of a GUI when the program starts. Here’s the StringBuilder code:

// memory tab
    StringBuilder mList = new StringBuilder();
    memLocList = new Memory[MEM_LOCATIONS];
    mem = new Memory();
    for (int i = 0; i < memLocList.length; i++) {
        memLocList[i] = mem;
        memLocList[i].setOpCode(00);
        mList.append(String.format("%10s %04x %10s %6s", "Address:   ", i,
                "Value:  ", memLocList[i].getOpCode()));
        mList.append("\n");
    }

JComponent memTab = makeTextPanel(mList.toString());
    tabs.addTab("Memory", new JScrollPane(memTab));

}

protected JComponent makeTextPanel(String t) {
    text = t;
    JPanel panel = new JPanel(false);
    JTextPane filler = new JTextPane();
    filler.setFont(new Font("Courier", Font.PLAIN, 14));
    filler.setText(text);
    filler.setAlignmentX(LEFT_ALIGNMENT);
    panel.setLayout(new GridLayout(1, 1));
    panel.add(filler);
    return panel;
}

The GUI also has a text entry panel where a String of hex values can be entered.

On clicking a button, the user is prompted for another value, which corresponds to the position in the array where the first hex value should be inserted.

Once these values have been entered, I’d like the display to be updated / refreshed to reflect this but am unsure of how to go about it.

I found this question here, which is similar but I’m not sure if implementing Observer/Observable pattern is the right way to proceed, and even if it is, how I’d go about it:
Best Way to Constantly Update GUI Elements

My initial approach was to add an “updateDisplay()” method, which I could call after processing the button click and re-call the makeTextPanel method:

public void updateDisplay() {

    makeTextPanel(text);
}

I thought this might refresh it but it has no effect of the display.

Any help appreciated.

Answer 1

You hold your array in a model class, and you allow other classes to “listen” to this by giving this class a SwingPropertyChangeSupport object as well as an addPropertyChangeListener(…) method. Then give the array a setXXX(…) method, and in that method fire the SwingPropertyChangeSupport object after updating the array. There are examples of just this sort of thing on this site, some written by me.

For example: here, here, here, …

By the way, I’m not surprised that your call to makeTextPanel(text) doesn’t work. It creates a JPanel, but you don’t appear to do anything with the JPanel that is returned from the method. But nor should you. I don’t think that creating new JPanels is the solution you want, but rather updating the Strings displayed by a component of some sort such as a JList or JTextArea using the listener framework that I’ve described above.

If any of this is confusing, please ask for clarification.