添加JPanel时，JScrollPane不显示滚动条 [英] JScrollPane doesn't show scroll bars when JPanel is added

问题描述

我尝试使用以下方法将JPanel添加到JScrollPane:

I'm tried to add a JPanel to a JScrollPane using:

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

，它奏效了.但是问题在于，即使Panel1较大，scrollPane也不显示滚动条. (我正在使用NetBeans，而panel1是jpanel形式)

and it worked. But the problem is scrollPane doesn't show scroll bars even the Panel1 is bigger. (I'm working with NetBeans & panel1 is a jpanel form)

推荐答案

覆盖， setPreferredSize()，尽管如API中所述

Override, getPreferredSize() method for the said JScrollPane, you might be able to see the Scroll Bar. Or one can simply call setPreferredSize(), though as stated in the API

设置此组件的首选大小.如果preferredSize为null，则会要求用户界面提供首选大小

Sets the preferred size of this component. If preferredSize is null, the UI will be asked for the preferred size

覆盖将是有益的，因为它倾向于为所述JComponent定义一些适当的尺寸.

overriding will be beneficial, as it tends to define some appropriate dimensions to the said JComponent.

类似这样的东西:

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);
    }
}

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