為什么JPanel沒有顯示在JScrollPane上？

Question

為什么JPanel panGraphics沒有顯示在JScrollPane ？ 但是，如果我將panGraphics直接放在JTabbedPane ，它將起作用： tabbedPaneData.addTab("Chart View", panGraphics);

JTabbedPane tabbedPaneData = new JTabbedPane();
JScrollPane paneScrollPane = new JScrollPane();

JPanel panGraphics = createGraphics();

paneScrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
paneScrollPane.setPreferredSize(new Dimension(550, 320));
paneScrollPane.setMinimumSize(new Dimension(10, 10));

paneScrollPane.add(panGraphics);

tabbedPaneData.addTab("Chart View", paneScrollPane);
tabbedPaneData.addTab("Table View", new JPanel());

Answer 1

使用方法JScrollPane.setViewportView添加面板。 因此，代替：

paneScrollPane.add(panGraphics);

采用：

paneScrollPane.setViewportView(panGraphics);

Answer 2

Here is My collection sample code:
-----------------------------------
package testing;

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;

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

public class TestScroller extends JPanel
{
    JPanel panel;
    JScrollPane scrollPane;

    public TestScroller() {
        // TODO Auto-generated constructor stub

//this is in the constructor of the mother object, JPanel
    panel = new JPanel();
    panel.setBorder(BorderFactory.createEtchedBorder());
    //panel.setBounds(0,0,415,420);

    panel.setPreferredSize(new Dimension(415,420));
    panel.setBackground(Color.BLACK);

    scrollPane = new JScrollPane(panel);
    scrollPane.setPreferredSize(new Dimension(415,400));
    add(scrollPane);
  //  add(scrollPane, 0, 40, 415, 400);
    }
/*  //method add defined in the mother object
      public void add(Component c, int x, int y, int sX, int sY)
      {
          add(c);
          c.setBounds(x,y,sX,sY);
      }*/




    public static void main( String args[] )
    {
        JPanel baseView = new TestScroller();
        baseView.setPreferredSize(new Dimension(500,500));
        baseView.setOpaque(false);
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(baseView);
        frame.setSize(500,500);

        frame.setVisible(true);
        frame.repaint();
    }
}