Name: jk109818 Date: 01/02/2002


java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-b24)
Java HotSpot(TM) Client VM (build 1.3.1-b24, mixed mode)


When Container.add(Component) is called, the Container's internal
addImpl method is called with a null constraints reference. If the
container's layout manager implements LayoutManager but not
LayoutManager2, the code in addImpl will only call
LayoutManager.addLayoutComponent(String, Component) if the constraints
reference refers to a String. If the constraints reference is
null, no call to addLayoutComponent occurs.

I encountered this problem when using the CardPanel code from an
article in The Swing Connection. The test program below illustrates
the problem.

  To fix the problem, I suggest the changing Container.addImpl from this:

} else if (constraints instanceof String) {
layoutMgr.addLayoutComponent((String)constraints, comp);
}
to:

} else if (constraints == null || constraints instanceof String)
{
layoutMgr.addLayoutComponent((String)constraints, comp);
}


import java.awt.*;
import java.awt.event.*;

import javax.swing.*;
import javax.swing.event.*;

public class ContainerAddProblem
{
public static void main(String[] args)
{
CardPanel cardPanel = new CardPanel();
JLabel label1 = new JLabel("One");
JLabel label2 = new JLabel("Two");
JLabel label3 = new JLabel("Three");

cardPanel.add(label1);
cardPanel.add(label2);
cardPanel.add(label3);

// Due to a bug in Container.addImpl, this
// shows card 2 instead of card 3.
cardPanel.showCard(label3);

JFrame frame = new JFrame();
frame.getContentPane().add(cardPanel);
frame.setSize(200, 100);
frame.setVisible(true);
}
}

/**
 * What follows is the CardPanel class from The Swing Connection, modified
 * only to make the class non-public for compiling as part of this file.
 * The source code was obtained from here:
 *
 * http://java.sun.com/products/jfc/tsc/articles/cardpanel/index.html
 * http://java.sun.com/products/jfc/tsc/articles/cardpanel/downloads/source.zip
 */

/**
 * A simpler alternative to a JPanel with a CardLayout. The AWT CardLayout
 * layout manager can be inconvenient to use because the special "stack of
 * cards" operations it supports require a cast to use. For example to show
 * the card named "myCard" given a JPanel with a CardLayout one would write:
 * <pre>
 * ((CardLayout)(myJPanel.getLayout())).show(myJPanel, "myCard");
 * </pre>
 * This doesn't work well with Swing - all of the CardLayout display operations,
 * like <code>show</code> call validate directly. Swing supports automatic
 * validation (see JComponent.revalidate()); this direct call to validate is
 * inefficient.
 * <p>
 * The CardPane JPanel subclass is intended to support a layout with a modest
number
 * of cards, on the order of 100 or less. A cards name is it's component
 * name, as in java.awt.Component.getName(), which is set when the component
 * is added to the CardPanel:
 * <pre>
 * myCardPanel.add(myChild, "MyChildName");
 * myChild.getName() <i>=> "MyChildName"</i>
 * </pre>
 * As with CardLayout, the first child added to a CardPanel is made visible
 * and there's only one child visible at a time. The <code>showCard</code>
 * method accepts either a childs name or the child itself:
 * <pre>
 * myCardPanel.show("MyChildName");
 * myCardPanel.show(myChild);
 * </pre>
 * <p>
 * The CardPanel class doesn't support the vgap/hgap CardLayout properties since
 * one can add a Border, see JComponent.setBorder().
 */

/*public*/ class CardPanel extends JPanel
{
    private static class Layout implements LayoutManager
    {
/**
* Set the childs name (if non-null) and and make it visible
* iff it's the only CardPanel child.
* @see java.awt.Component#setName
*/
public void addLayoutComponent(String name, Component child) {
if (name != null) {
child.setName(name);
}
child.setVisible(child.getParent().getComponentCount() == 1);
}

/**
* If this child was visible, then make the first remaining
* child visible.
*/
public void removeLayoutComponent(Component child) {
if (child.isVisible()) {
Container parent = child.getParent();
if (parent.getComponentCount() > 0) {
parent.getComponent(0).setVisible(true);
}
}
}

/**
* @return the maximum preferred width/height + the parents insets
*/
public Dimension preferredLayoutSize(Container parent) {
int nChildren = parent.getComponentCount();
Insets insets = parent.getInsets();
int width = insets.left + insets.right;
int height = insets.top + insets.bottom;

for (int i = 0; i < nChildren; i++) {
Dimension d = parent.getComponent(i).getPreferredSize();
if (d.width > width) {
width = d.width;
}
if (d.height > height) {
height = d.height;
}
}
return new Dimension(width, height);
}

/**
* @return the maximum minimum width/height + the parents insets
*/
public Dimension minimumLayoutSize(Container parent) {
int nChildren = parent.getComponentCount();
Insets insets = parent.getInsets();
int width = insets.left + insets.right;
int height = insets.top + insets.bottom;

for (int i = 0; i < nChildren; i++) {
Dimension d = parent.getComponent(i).getMinimumSize();
if (d.width > width) {
width = d.width;
}
if (d.height > height) {
height = d.height;
}
}
return new Dimension(width, height);
}

public void layoutContainer(Container parent) {
int nChildren = parent.getComponentCount();
Insets insets = parent.getInsets();
for (int i = 0; i < nChildren; i++) {
Component child = parent.getComponent(i);
if (child.isVisible()) {
Rectangle r = parent.getBounds();
int width = r.width - insets.left + insets.right;
int height = r.height - insets.top + insets.bottom;
child.setBounds(insets.left, insets.top, width, height);
break;
}
}
}
    }


    /**
     * Creates a CardPanel. Children, called "cards" in this API, should be
added
     * with add(). The first child we be made visible, subsequent children will
     * be hidden. To show a card, use one of the show*Card methods.
     */
    public CardPanel() {
super(new Layout());
    }

    
    /**
     * Return the index of the first (and one would hope - only)
     * visible child. If a visible child can't be found,
     * perhaps the caller has inexlicably hidden all of the
     * children, then return -1.
     */
    private int getVisibleChildIndex() {
int nChildren = getComponentCount();
for (int i = 0; i < nChildren; i++) {
Component child = getComponent(i);
if (child.isVisible()) {
return i;
}
}
return -1;
    }


    /**
     * Hide the currently visible child "card" and show the
     * specified card. If the specified card isn't a child
     * of the CardPanel then we add it here.
     */
    public void showCard(Component card) {
if (card.getParent() != this) {
add(card);
}
int index = getVisibleChildIndex();
if (index != -1) {
getComponent(index).setVisible(false);
}
card.setVisible(true);
revalidate();
repaint();
    }


    /**
     * Show the card with the specified name.
     * @see java.awt.Component#getName
     */
    public void showCard(String name) {
int nChildren = getComponentCount();
for (int i = 0; i < nChildren; i++) {
Component child = getComponent(i);
if (child.getName().equals(name)) {
showCard(child);
break;
}
}
    }


    /**
     * Show the card that was added to this CardPanel after the currently
     * visible card. If the currently visible card was added last, then
     * show the first card.
     */
    public void showNextCard() {
if (getComponentCount() <= 0) {
return;
}
int index = getVisibleChildIndex();
if (index == -1) {
showCard(getComponent(0));
}
else if (index == (getComponentCount() - 1)) {
showCard(getComponent(0));
}
else {
showCard(getComponent(index + 1));
}
    }


    /**
     * Show the card that was added to this CardPanel before the currently
     * visible card. If the currently visible card was added first, then
     * show the last card.
     */
    public void showPreviousCard() {
if (getComponentCount() <= 0) {
return;
}
int index = getVisibleChildIndex();
if (index == -1) {
showCard(getComponent(0));
}
else if (index == 0) {
showCard(getComponent(getComponentCount() - 1));
}
else {
showCard(getComponent(index -1));
}
    }


    /**
     * Show the first card that was added to this CardPanel.
     */
    public void showFirstCard() {
if (getComponentCount() <= 0) {
return;
}
showCard(getComponent(0));
    }


    /**
     * Show the last card that was added to this CardPanel.
     */
    public void showLastCard() {
if (getComponentCount() <= 0) {
return;
}
showCard(getComponent(getComponentCount() - 1));
    }
}
(Review ID: 136124)
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