How to Drill Down to a JList within a JScrollPane from another function

Question

I am creating a JList like so:

JScrollPane scrollPane = new JScrollPane();
scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
GridBagConstraints gbc_scrollPane = new GridBagConstraints();
gbc_scrollPane.insets = new Insets(0, 0, 5, 5);
gbc_scrollPane.fill = GridBagConstraints.BOTH;
gbc_scrollPane.gridx = 0;
gbc_scrollPane.gridy = 1;
contentPanel.add(scrollPane, gbc_scrollPane);
{
    JList listAvail = new JList();
    listAvail.setBorder(new TitledBorder(null, "", TitledBorder.LEADING, TitledBorder.TOP, null, null));    
    scrollPane.setViewportView(listAvail);
}

and I'm trying to access it when a button is clicked:

JButton btnAdd = new JButton("Add ->");
btnAdd.addMouseListener(new MouseAdapter()
{
    @Override
    public void mouseClicked(MouseEvent arg0)
    {
        if (!listAvail.isSelectionEmpty())
        {
            int[] selects = listAvail.getSelectedIndices();
            for (int i = selects.length - 1; i >= 0; i--)
            {
                appliedM.add(0, availM.getElementAt(selects[i]));
                appliedFeatures.add(0, availFeatures.get(selects[i]));
                availFeatures.remove(availFeatures.get(selects[i]));
                availM.remove(selects[i]);
            }
        }
    }
});

Of course, I'm getting an error saying "listAvail cannot be resolved" since it's out of the button's scope. Is there a getter method or a way to drill down to a specific component? I'm thinking something along the lines of:

contentPanel.scrollPane.listAvail

There must be something I'm missing but I haven't seen anything like this in the docs.

Edit: I am asking specifically about drilling down to a swing component. This is not a generic variable scoping question and not an exact duplicate of the referenced question. This question has yet to be answered at the time of this edit.

Hovercraft Full Of Eels · Answer 1 · 2017-06-07T02:35:01.733

2

Your question boils down to -- how do I access an object reference when it is assigned to a very locally scoped variable, here the object being the JList, and the variable it's being assigned to is listAvail, a variable buried within its own set of curly braces (why?) within a method or constructor.

The solution -- get the variable declaration out of the local scope and make it instead an instance field of the class. e.g.,

public class MyClass {
    private JList listAvail = new JList(); // should be generic btw

Another issue is here:

btnAdd.addMouseListener(new MouseAdapter() {....

Don't use a MouseListener with a JButton where an ActionListener is much more appropriate. This has ramifications if you want the button's actions to be disabled when the button itself is disabled.

edited Jun 07 '17 at 02:35

answered Jun 07 '17 at 02:27

Hovercraft Full Of Eels

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Answered as a community wiki until I could find a dupe – Hovercraft Full Of Eels Jun 07 '17 at 02:28
First, to answer your question about the curly braces: They were put there automatically by WindowBuilder and I'm afraid to delete something which might be important. – Z. Reticulan Jun 07 '17 at 02:30
@Chris: Don't use a window builder until you understand the language and the library. Seriously, else you will end up painting yourself into corners too often. – Hovercraft Full Of Eels Jun 07 '17 at 02:31
Your solution presented here was my initial idea. I made the variable an instance variable, but that caused all the UI components to move around the dialog and change positions on subsequent openings. – Z. Reticulan Jun 07 '17 at 02:34
@Chris: read the tutorials, learn the Java language and the Swing library is about all I can tell you at this point. .... Or move to JavaFX, a more modern Java GUI library. – Hovercraft Full Of Eels Jun 07 '17 at 02:35
Do you know if there is a way to drill down to a specific swing component? My question was marked as a duplicate so I doubt I will get an answer from anyone else. – Z. Reticulan Jun 07 '17 at 02:41
Yes, and the best answer -- don't do it it's ludicrous to try to base your model on the structure of the view as the GUI structure is brittle and likely to change. Really, don't go this route. – Hovercraft Full Of Eels Jun 07 '17 at 02:46
I don't understand. Respectfully, I'd rather leave personal opinions aside on a question and answer site. I'm simply asking for help on how to drill down to a nested swing component because I was unable to find it in the Java documentation. – Z. Reticulan Jun 07 '17 at 02:57
@Chris: Your documentation is here: [Component API](http://docs.oracle.com/javase/8/docs/api/java/awt/Component.html) and [Container API](http://docs.oracle.com/javase/8/docs/api/java/awt/Container.html). You would have to search containers for their components using `getComponents()`, check to see which components *are* containers, and then recursively search -- a holy mess. – Hovercraft Full Of Eels Jun 07 '17 at 03:04

How to Drill Down to a JList within a JScrollPane from another function

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