我的JScrollPane不滚动

Question

I'm having some trouble with a JScrollPane . When the pane limits exceeds, it does not scroll. Any tips?

With this code, the ScrollBar is shown on the left, but it doesn't work...

package gui;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class MainPanel  extends JPanel implements ActionListener
{
   private JLabel welcome = new JLabel ("\n  Insert your search type: \n");
   private JPanel radioPanel = new JPanel (new GridLayout (0,4));
   private FieldPanel name = new FieldPanel ("Name: " , 50);
   private FieldPanel year = new FieldPanel ("Year: " , 3);
   private FieldPanel genre = new FieldPanel ("Genre: " , 10);
   private FieldPanel rating = new FieldPanel ("Users' rating (1-5): " , 2);
   private JButton search = new JButton ("Search");
   private JButton clear = new JButton ("Clear");
   private JScrollPane scroll;   
   private JFormattedTextField textField;

   public MainPanel () 
   {
       ButtonGroup RBGroup = new ButtonGroup ();

       // Cria radio buttons
       JRadioButton nameRB      = new JRadioButton ("Name");
       JRadioButton yearRB      = new JRadioButton ("Year");
       JRadioButton genreRB     = new JRadioButton ("Genre");
       JRadioButton ratingRB    = new JRadioButton ("Rating");

       // Seta comandos para os radio buttons
       nameRB.setActionCommand("nameOfMovie");
       yearRB.setActionCommand("dataReleaseOfMovie");
       genreRB.setActionCommand("genreOfMovie");
       ratingRB.setActionCommand("noteOfMovie");

       // Seta o nome como padrao inicial
       nameRB.setSelected(true);

       // Adicionar radio buttons em um grupo
       RBGroup.add (nameRB);
       RBGroup.add (yearRB);
       RBGroup.add (genreRB);
       RBGroup.add (ratingRB);

       // Adicionar action listeners ao radio buttons
       nameRB.addActionListener(this);
       yearRB.addActionListener(this);
       genreRB.addActionListener(this);
       ratingRB.addActionListener(this);

       radioPanel.add(nameRB);
       radioPanel.add(yearRB);
       radioPanel.add(genreRB);
       radioPanel.add(ratingRB);

       // Adicionar coisinhas
       add (welcome);
       add (radioPanel);
       add (name);
       add (year);
       add (genre);
       add (rating);
       add (search);
       add (clear);

       // Adicionar action listeners nos botoes
       search.addActionListener(this);
       clear.addActionListener(this);

       // Criar e adicionar painel para exibir informacoes do filme
       JPanel informations = new JPanel ();
       informations.setLayout (new BoxLayout(informations, BoxLayout.Y_AXIS));
       informations.setPreferredSize(new Dimension(767,461));

       scroll = new JScrollPane(informations);
       scroll.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);  
       scroll.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

       add (scroll);

       informations.add(new JLabel ("oi oi oi oi oi oio i\noioioioioi"));
       informations.add(new JLabel ("uhuuul"));
       informations.add(new JLabel ("uhuuul"));
       //repeats 100 times, just to test the scroll
       informations.add(new JLabel ("fim"));
       //setLayout (new FlowLayout (FlowLayout.LEFT));

   }


   public void actionPerformed (ActionEvent e)
   {
       Object obj = e.getSource ();

       if (obj == search)
       {
           // Pegar as coisas dos edit text pra salvar
       }
       else if (obj == clear)
       {
           name.setTextField ("");
           year.setTextField ("");
           genre.setTextField ("");
           rating.setTextField ("");
       }
   }
}

I added the informations.add just for testing the JScrollPane .

Answer 1

You have a problem here in the JPanel view that you add to your JScrollPane:

informations.setPreferredSize(new Dimension(767,461));

This limits the size of the JPanel, no matter what its contents are. Don't do this. Instead, let the JPanel get larger as you add more components to it.

If you need to set the preferred size of anything (kleo forgive me), it should be the JScrollPane or its viewport:

scroll.getViewport().setPreferredSize(new Dimension(767, 461));

Though myself, I'd consider using a JList and setting its visibleRowCount:

  DefaultListModel<String> listModel = new DefaultListModel<>();
  JList<String> infoList = new JList<>(listModel);

  infoList.setVisibleRowCount(20);

  listModel.addElement("oi oi oi oi oi oio i\noioioioioi");
  listModel.addElement("uhuuul");
  listModel.addElement("uhuuul");
  for (int i = 0; i < 100; i++) {
     listModel.addElement("uhuuul");
  }
  listModel.addElement("fim");

  JScrollPane scrollPane = new JScrollPane(infoList);
  scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

  add(scrollPane);