添加JPanel时,JScrollPane不显示滚动条

Question

我尝试使用以下命令将JPanel添加到JScrollPane:

    panel1 Panel1 = new panel1(); 
    jScrollPane1.setViewportView(Panel1);

它起作用了.但问题是scrollPane不显示滚动条甚至Panel1更大.(我正在使用NetBeans&panel1是一个jpanel表单)

Answer 1

对于所述的覆盖,getPreferredSize()方法JScrollPane,您可能会看到滚动条.或者可以简单地调用setPreferredSize(),尽管如API中所述

设置此组件的首选大小.如果preferredSize为null,则将要求UI提供首选大小

压倒将是有益的,因为它倾向于定义一些适当的尺寸JComponent.

像这样的东西:

JScrollPane scroller = new JScrollPane() {
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 200);
    }
};
scroller.setViewportView(panelWithScroll);

一个例子:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class PanelScroller {

    private void displayGUI() {
        JFrame frame = new JFrame("Swing Worker Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        JPanel contentPane = new JPanel();
        JPanel panelWithScroll = new JPanel();
        panelWithScroll.setLayout(new GridLayout(0, 1, 5, 5));
        JScrollPane scroller = new JScrollPane() {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(300, 200);
            }
        };
        scroller.setViewportView(panelWithScroll);
        //scroller.setPreferredSize(new Dimension(300, 200));

        for (int i = 0; i < 20; i++) {
            panelWithScroll.add(new JLabel(Integer.toString(i + 1), JLabel.CENTER));
        }

        contentPane.add(scroller);

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                new PanelScroller().displayGUI();
            }
        };
        EventQueue.invokeLater(runnable);
    }
}