JScrollPane在鼠标滚动或调整框架大小之前不显示内容

Question

我也看过这个问题，但没有帮助：添加JPanel时JScrollPane不显示滚动条

使用空布局是有意的，我正在做我自己的格式化，而不是考虑多个大小的屏幕。提前感谢！

class FilesPanel extends JPanel
{
    public JScrollPane scroller;
    private FileHolderPanel holder;

    public FilesPanel()
    {
        //setLayout(null);
        setBackground(extraLight);

        holder = new FileHolderPanel();

        System.out.println(holder.getWidth() + " " + holder.getHeight() + " " + holder.getX() + " " + holder.getY() + " " + holder.getBounds());

        scroller = new JScrollPane();

        JViewport viewport = new JViewport();
        viewport.add(holder);
        scroller.setViewport(viewport);

        scroller.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        scroller.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);

        scroller.setBorder(BorderFactory.createEmptyBorder());
        scroller.setBackground(blue);
        add(scroller);
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        scroller.setLocation(0, 0);
        scroller.setSize(filesWidth, frame.getHeight() - 40);
    }

    class FileHolderPanel extends JPanel
    {
        public FileHolderPanel()
        {
            setBackground(extraLight);
            setLayout(null);
            setVisible(true);
        }

        public void paintComponent(Graphics g)
        {
            super.paintComponent(g);
        }
    }
}

Answer 1

“主要”问题是FileHolderPanel不知道它可能希望的大小，因此JScrollPane不知道它需要多大，也不知道它应该何时显示滚动条。这是一个猜测工作，因为您没有提供一个完全可运行的示例。

下面的例子很好...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new ContentPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class ContentPane extends JPanel {

        public ContentPane() {
            setLayout(new BorderLayout());
            JScrollPane scrollPane = new JScrollPane(new FileHolderPane());
            scrollPane.setBorder(BorderFactory.createEmptyBorder());
            scrollPane.setBackground(Color.BLUE);
            add(scrollPane);
        }

    }

    public class FileHolderPane extends JPanel {

        public FileHolderPane() {
            setBackground(Color.RED);
            setLayout(new GridBagLayout());
            add(new JLabel("All your content is belong to us"));
        }

        @Override
        public Dimension getPreferredSize() {
            // This will make the panel a fixed size, so beware of that
            return new Dimension(400, 400);
        }

    }
}

如果您需要更多的控制，那么您可能需要查看可滚动接口，但这是另一个复杂程度