【javaSE】JPanel+FLowLayout加垂直滚动条...

[dosgege]

代码

class ModifiedFlowLayout extends FlowLayout {

    public ModifiedFlowLayout() {
        super();
    }

    public ModifiedFlowLayout(int align) {
        super(align);
    }

    public ModifiedFlowLayout(int align, int hgap, int vgap) {
        super(align, hgap, vgap);
    }

    public Dimension minimumLayoutSize(Container target) {
        return computeSize(target, false);
    }

    public Dimension preferredLayoutSize(Container target) {
        return computeSize(target, true);
    }

    private Dimension computeSize(Container target, boolean minimum) {
        synchronized (target.getTreeLock()) {
            int hgap = getHgap();
            int vgap = getVgap();
            int w = target.getWidth();

            if (w == 0) {
                w = Integer.MAX_VALUE;            	
            }

            Insets insets = target.getInsets();
            if (insets == null) {
                insets = new Insets(0, 0, 0, 0);
            }
            int reqdWidth = 0;

            int maxwidth = w - (insets.left + insets.right + hgap * 2);
            int n = target.getComponentCount();
            int x = 0;
            int y = insets.top;
            int rowHeight = 0;

            for (int i = 0; i < n; i++) {
                Component c = target.getComponent(i);
                if (c.isVisible()) {
                    Dimension d =
                            minimum ? c.getMinimumSize() : c.getPreferredSize();
                    if ((x == 0) || ((x + d.width) <= maxwidth)) {
                        if (x > 0) {
                            x += hgap;
                        }
                        x += d.width;
                        rowHeight = Math.max(rowHeight, d.height);
                    } else {
                        x = d.width;
                        y += vgap + rowHeight;
                        rowHeight = d.height;
                    }
                    reqdWidth = Math.max(reqdWidth, x);
                }
            }
            y += rowHeight;
            return new Dimension(reqdWidth + insets.left + insets.right, y);
        }
    }
}
  
public class SimpleTest extends JPanel{   
    private ImageIcon image;   
    private JLabel label;   
    private JButton button;   
    private JPanel buttonPanel, imagePanel;   
    private JScrollPane scrollPane;   
       
    public SimpleTest(){          
    	this.setLayout(new BorderLayout());
           
        button = new JButton("Add Image");   
        button.setPreferredSize(new Dimension(80, 25));   
        button.setMargin(new Insets(0, 5, 0, 5));   
           
        image = new ImageIcon("E:\\tobacco\\img\\folder.png");   
        imagePanel = new JPanel(new ModifiedFlowLayout(FlowLayout.LEFT, 5, 5));   
        for(int i=0;i<12;i++)
        {
		     label = new JLabel(image);
		     //label.setPreferredSize(new Dimension(100,100));//为什么添加此句，滚动条显示错误？
		     imagePanel.add(label);  		     
	    } 
        
        scrollPane = new JScrollPane(imagePanel); 
        
        button.addActionListener(new ActionListener(){   
            public void actionPerformed(ActionEvent e){ 
            	
                label = new JLabel(image);   
                imagePanel.add(label);   
                validate();   
            }   
        });   
  
        buttonPanel = new JPanel(new FlowLayout(FlowLayout.LEFT, 0, 0));   
        buttonPanel.add(button);
           
        add(buttonPanel, BorderLayout.NORTH);   
        add(scrollPane, BorderLayout.CENTER);  
    }   
       
    public static void main(String[] args) {  
    	JFrame jf =new JFrame();
    	jf.setDefaultCloseOperation(jf.EXIT_ON_CLOSE);
    	jf.setBounds(200,50,480,300);
    	
    	
    	jf.add(new SimpleTest());
    	
    	jf.setVisible(true);
    }   
}  

问题：当设置面板中组件的preferredSize后，滚动条显示就有问题？具体看第2个类的代码注释行。

求解释，求解决办法！