当框架太小而无法显示所有JList时，如何让滚动条出现在JList上？

Question

I want to make a scrollbar appear on a JList whenever the frame is resized to be too small for the List itself. So far, this is the code I have. Run it, resize the frame, and notice how no scrollbar ever appears on the JList.

import java.awt.Dimension;

import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;


public class JListScroll extends JPanel{

JScrollPane listScrollPane;

public JListScroll() {
    String[] stringArray = {"Testing","This","Stuff"};
    JList<String> rowList = new JList<String>(stringArray);
    listScrollPane = new JScrollPane();
    listScrollPane.getViewport().setView(rowList);
    this.setSize(new Dimension(75,200));
    this.add(listScrollPane);
    this.doLayout();
}

public static void main(String[] args){
    JFrame frame = new JFrame();
    JListScroll scrollPanel = new JListScroll();
    frame.add(scrollPanel);
    frame.setVisible(true);
    frame.setSize(new Dimension(75,300));
}

}

Notice how there is a JScrollPane added, but no scroll bar appears on the list when the window gets really small. This is what I want to fix.

Thanks in advance!

Answer 1

• JPanel has implemented FlowLayout

• FlowLayout accepting only PreferredSize (in your case hardcoded by setSize)

• FlowLayout isn't designated, not implemented any resize JComponents (layed by FlowLayout) together with container, JComponent isn't resizable, stays as it is

• don't want to commenting something about your code posted here, see differencies, quite good low level

import java.awt.BorderLayout;
import java.awt.Dimension;    
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class JListScroll {

    private JFrame frame = new JFrame();
    private JPanel panel = new JPanel();
    private JScrollPane listScrollPane = new JScrollPane();
    private String[] stringArray = {"Testing", "This", "Stuff"};
    private JList rowList = new JList(stringArray);

    public JListScroll() {
        rowList.setVisibleRowCount(2);
        listScrollPane.setViewportView(rowList);
        panel.setLayout(new BorderLayout());
        panel.add(listScrollPane);
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // EDIT 
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JListScroll jListScroll = new JListScroll();
            }
        });
    }
}

Answer 2

您可以使用方法listScrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS)强制（垂直）滚动条的可见性