Cannot add to a JList when list is added to a JScrollPane

Question

I wrote a program which select files and adds them to a JList. The program works fine, and the code to add the files to the list is like this:

JPanel pane;
File newFile[];
static List<File> files = new ArrayList<File>();
static DefaultListModel<File> listModel = new DefaultListModel<>();
JList<File> fileList = new JList<>(listModel);

JPanel listPane = new JPanel();
pane.add(listPane, BorderLayout.CENTER);
listPane.setBackground(Color.LIGHT_GRAY);
listPane.setBorder(new EmptyBorder(0, 20, 0, 0));
listPane.setLayout(new BorderLayout());
listPane.add(fileList);
}
void getFile() {
    final JFileChooser fc = new JFileChooser();
    fc.setDialogTitle("Select File...");
    fc.setApproveButtonText("Select");
    fc.setMultiSelectionEnabled(true);
    int returnVal = fc.showOpenDialog(pane);
    if (returnVal == JFileChooser.APPROVE_OPTION) {
        newFile = fc.getSelectedFiles();
    }
}
void setFile() {
    int i = 0;
    while (i < newFile.length) {
        files.add(newFile[i]);
        listModel.addElement(newFile[i]);
        i++;
    }
}

This is the base code for selecting and adding the files. So now I want to have a scrollbar on the pane, so I modified it to a JScrollPane like this:

JScrollPane listPane = new JScrollPane();
pane.add(listPane, BorderLayout.CENTER);
listPane.setBackground(Color.LIGHT_GRAY);
listPane.setBorder(new EmptyBorder(0, 20, 0, 0));
listPane.setViewportView(fileList);
listPane.add(fileList);
}

So everything compiles without errors, but nothing is added to the JScrollPane. It is my understanding that a JScrollPane can be used like a regular JPanel, except it will have scrollbars when overflowed. Is there something about JScrollPanes that I am missing here?

Recommendations: 1) Add the list to the scroll pane when the scroll pane is created and added to the GUI. 2) Thereafter, only deal with (add items to or remove them from) the model. 3) Remove `static List files = new ArrayList();` and get any information or `File` direct from the model. 4) Remove the `static` prefix from `static DefaultListModel listModel = new DefaultListModel<>();`. Static is rarely the correct solution (to whatever the problem is). 5) For better help sooner, post a [MCVE] or [Short, Self Contained, Correct Example](http://www.sscce.org/). — Andrew Thompson, Mar 23 '16 at 07:11

score 3 · Accepted Answer · edited May 23 '17 at 12:23

3

try removing

listPane.add(fileList); //remove

you should use setViewportView() method to add a component to scrollpane.and you have done it.so you don't need to add again by calling listPane.add .

example

JScrollPane listPane = new JScrollPane();
pane.add(listPane, BorderLayout.CENTER);
listPane.setBackground(Color.LIGHT_GRAY);
listPane.setBorder(new EmptyBorder(0, 20, 0, 0));
listPane.setViewportView(fileList);
// removed add line

also you can pass component that you want to add to scrollpane by passing to scroll pane constructor as thompson said.

JScrollPane listPane = new JScrollPane(fileList);

also as thompson said you should avoid declaring listModel ,files .you should read more about static keyword and when you should use it .

edited May 23 '17 at 12:23

Community

1
1

answered Mar 23 '16 at 04:59

Madhawa Priyashantha

9,633
7
33
60

I prefer `JScrollPane listPane = new JScrollPane(fileList); // add the only component this scroll pane will ever show, at time of construction` (perhaps without the verbose comment). ;) – Andrew Thompson Mar 23 '16 at 07:16
That did it. Also, to streamline it a little more, I tried out Andrew's suggestion of adding it right to the `JScrollPane` constructor, which also worked. Both awesome solutions. Thanks guys. – user3226170 Mar 24 '16 at 20:40

Cannot add to a JList when list is added to a JScrollPane

1 Answers1