Java Swing - 常识篇 之 LayoutManager 03

        这篇还是继续讲Swing的常识，主要是针对想成为Swing“高手”的新接触的朋友。在这里想说一下题外话，Swing这种技术虽然很“老旧”，但是又有几个人能完完全全熟透Swing呢，在很多人的眼里都认为Swing很复杂，但是如果把Swing弄懂了之后，其他的JavaFX、SWT、Android的界面开发，其实也不再话下。其实界面开发都是差不多的，一个样。在这里想告诉大家一个道理，别看到新技术就一头扎进去。如果熟练掌握Swing，而又熟悉JavaFX的朋友，可能会发现JDK下的com.sun.java.swing包下的很多东西都和JavaFX的特效相似.

      上两篇文章介绍完了两个非常好用的LayoutManager（MigLayout和TableLayout），今天在这里将会讲述一下CardLayout，介绍它如何使用，哪些地方存在不足。

      先看看API对CardLayout的描述：它将容器中的每个组件看作一张卡片。一次只能看到一张卡片，容器则充当卡片的堆栈。当容器第一次显示时，第一个添加到 CardLayout对象的组件为可见组件。然后我们再看看它的方法，不难发现，它的几个重要的方法如下：

first(Container) ：Flips to the first card of the container.

last(Container）： Flips to the last card of the container.

next(Container)：Flips to the next card of the specified container.

previous(Container)：Flips to the previous card of the specified container.

show(Container)：Flips to the component that was added to this layout with the specified name, using addLayoutComponent.

    下面先来看一个例子：

package org.dui.sample;

import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

import net.miginfocom.swing.MigLayout;


/**
 * <code>CardLayoutSample</code> demonstrates how to use the
 * <code>CardLayout</code>
 * 
 * @author Jimmy
 * @since <i> DUI v1.0.0 (Apr 1,2013)</i>
 */
public class CardLayoutSample extends JPanel {
	private static final long serialVersionUID = 1L;
	/**Cache the index of the current displaying component*/
	private int m_iCurrent = 0;
	{
		try {
			UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
			UIManager.put("Label.font", new Font("", Font.BOLD, 20));
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	/**
	 * Just create an instance.
	 * 
	 */
	public CardLayoutSample() {
		initGUI();
	}

	/**
	 * Init the UI
	 *
	 * @since <i>DUI v.1.0.0 (Apr 1, 2013)</i>
	 */
	public void initGUI() {
		this.setLayout(new MigLayout("ins 5", "grow,fill", "[grow,fill][fill]"));
		this.setPreferredSize(new Dimension(400,300));
		
		final CardLayout layoutCard = new CardLayout();
		final JPanel pnlCard = new JPanel(layoutCard);
		JButton btnPrev = new JButton("Prev");
		JButton btnNext = new JButton("Next");
		this.add(pnlCard, "cell 0 0")
		.add(btnPrev, "cell 0 1, gapleft push")
		.add(btnNext, "cell 0 1, gapright push");
		
		final String[] aNames = {"card1","card2", "card3", "card4"};
		pnlCard.add(new JLabel("Card1"), aNames[0]);
		pnlCard.add(new JLabel("Card2"), aNames[1]);
		pnlCard.add(new JLabel("Card3"), aNames[2]);
		pnlCard.add(new JLabel("Card4"), aNames[3]);
		
		btnPrev.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				m_iCurrent = m_iCurrent >= 1 ? --m_iCurrent : m_iCurrent;
				layoutCard.show(pnlCard, aNames[m_iCurrent]);
			}
		});
		
		btnNext.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				m_iCurrent = m_iCurrent < 3 ? ++m_iCurrent : m_iCurrent;
				layoutCard.show(pnlCard, aNames[m_iCurrent]);
			}
		});
	}
	
	/**
	 * Add a Component specify by <code>oComp</code> to the container <code>self</code>
	 * @param oComp
	 * @param oConstraints
	 * @return self
	 *
	 * @since <i>DUI v.1.0.0 (Apr 1, 2013)</i>
	 */
	public CardLayoutSample add(JComponent oComp, Object oConstraints){
		super.add(oComp, oConstraints);
		return this;
	}
	
	
	public static void main(String[] args) {
		SwingUtilities.invokeLater(new Runnable() {
			@Override
			public void run() {
				JFrame oFrame = new JFrame();
				oFrame.setTitle("CardLayoutSample");
				oFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				oFrame.setResizable(true);
				oFrame.setContentPane(new CardLayoutSample());
				oFrame.pack();
				oFrame.setVisible(true);
				oFrame.setLocationRelativeTo(null);
			}
		});
	}
	
}

           看了上面的例子，细心的你可能会发现，在程序中要用m_iCurrent来记录当前CarLayout所显示的组件，其实CardLayout有两个做得不够好的地方：

1）CardLayout没有提供方法去获取当前正在显示的组件。

2）当开始显示的整个Container的时候，CardLayout里面的组件没有得到聚焦。

为了解决上面两个问题，在这里提供一个增强版的CardLayout 命名为RCardLayout。例子在这里就不再写了，如果不会使用的朋友，可以留言。

package org.dui.sample;

import java.awt.CardLayout;
import java.awt.Component;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.HierarchyEvent;
import java.awt.event.HierarchyListener;
import java.util.ArrayList;

import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JComponent;

/**
 * The <code>RCardLayout</code> provides some extensions to the CardLayout
 * class. In particular adding support for:
 * 
 * a) setting focus on the card when it is displayed b) getting the currently
 * displayed Card c) Next and Previous Actions This added support will only work
 * when a JComponent is added as a Card.
 * 
 * @since <i> DUI v1.0.0 (Apr 1,2013)</i>
 * 
 */
public class RCardLayout extends CardLayout implements HierarchyListener {
	private static final long serialVersionUID = 1L;
	private ArrayList<JComponent> cards = new ArrayList<JComponent>();
	private JComponent firstCard;
	private JComponent lastCard;
	private JComponent currentCard;
	private boolean isRequestFocusOnCard = true;
	private Action nextAction;
	private Action previousAction;

	/**
	 * Creates a new card layout with gaps of size zero.
	 */
	public RCardLayout() {
		this(0, 0);
	}

	/**
	 * Creates a new card layout with the specified horizontal and vertical
	 * gaps. The horizontal gaps are placed at the left and right edges. The
	 * vertical gaps are placed at the top and bottom edges.
	 * 
	 * @param hgap
	 *            the horizontal gap.
	 * @param vgap
	 *            the vertical gap.
	 */
	public RCardLayout(int hgap, int vgap) {
		super(hgap, vgap);
	}

	// Overridden methods

	public void addLayoutComponent(Component comp, Object constraints) {
		super.addLayoutComponent(comp, constraints);

		if (!(comp instanceof JComponent))
			return;

		JComponent component = (JComponent) comp;
		cards.add(component);

		if (firstCard == null)
			firstCard = component;

		lastCard = component;

		component.addHierarchyListener(this);
	}

	public void removeLayoutComponent(Component comp) {
		super.removeLayoutComponent(comp);

		if (!(comp instanceof JComponent))
			return;

		JComponent component = (JComponent) comp;
		component.removeHierarchyListener(this);
		cards.remove(component);

		if (component.equals(firstCard) && cards.size() > 0) {
			firstCard = cards.get(0);
		}

		if (component.equals(lastCard) && cards.size() > 0) {
			lastCard = cards.get(cards.size() - 1);
		}

	}

	// New methods

	public JComponent getCurrentCard() {
		return currentCard;
	}

	public Action getNextAction() {
		return getNextAction("Next");
	}

	public Action getNextAction(String name) {
		if (nextAction == null) {
			nextAction = new CardAction(name, true);
			nextAction.putValue(Action.MNEMONIC_KEY, (int) name.charAt(0));
			nextAction.setEnabled(isNextCardAvailable());
		}

		return nextAction;
	}

	public Action getPreviousAction() {
		return getPreviousAction("Previous");
	}

	public Action getPreviousAction(String name) {
		if (previousAction == null) {
			previousAction = new CardAction(name, false);
			previousAction.putValue(Action.MNEMONIC_KEY, (int) name.charAt(0));
			previousAction.setEnabled(isNextCardAvailable());
		}

		return previousAction;
	}

	public boolean isNextCardAvailable() {
		return currentCard != lastCard;
	}

	public boolean isPreviousCardAvailable() {
		return currentCard != firstCard;
	}

	public boolean isRequestFocusOnCard() {
		return isRequestFocusOnCard;
	}

	public void setRequestFocusOnCard(boolean isRequestFocusOnCard) {
		this.isRequestFocusOnCard = isRequestFocusOnCard;
	}

	// Implement Hierarchy Listener

	@Override
	public void hierarchyChanged(HierarchyEvent e) {
		JComponent component = (JComponent) e.getSource();

		if ((HierarchyEvent.SHOWING_CHANGED & e.getChangeFlags()) != 0 && component.isShowing()) {
			currentCard = component;

			if (isRequestFocusOnCard)
				currentCard.transferFocus();

			if (nextAction != null)
				nextAction.setEnabled(isNextCardAvailable());

			if (previousAction != null)
				previousAction.setEnabled(isPreviousCardAvailable());
		}
	}

	class CardAction extends AbstractAction {
		private static final long serialVersionUID = 1L;
		private boolean isNext;

		public CardAction(String text, boolean isNext) {
			super(text);
			this.isNext = isNext;
			putValue(Action.SHORT_DESCRIPTION, getValue(Action.NAME));
		}

		public void actionPerformed(ActionEvent e) {
			Container parent = getCurrentCard().getParent();

			if (isNext)
				next(parent);
			else
				previous(parent);
		}
	}
}