利用Observer模式解决组件间通信问题

//LeftPanel.java
package com.jungleford.test;
import java.awt.BorderLayout;
import javax.swing.*;
import javax.swing.event.TreeSelectionListener;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.tree.DefaultMutableTreeNode;
import java.util.Observable;
import java.util.Observer;
public final class LeftPanel extends JPanel
{// 把树型选择视图布局在左边
private JTree tree;// 树型选择视图
private JScrollPane scroll;// 让视图可滚动
private DefaultMutableTreeNode root, node1, node2;// 根节点及两个叶子
private Sensor sensor;// sensor是一个Observable，由于只能单根继承，所以作为组合成员
private String file;// 图片文件名，与RightPanel通信的内容
public LeftPanel(Observer observer)
{
file = "";
sensor = new Sensor();
sensor.addObserver(observer);// 向Observable注册Observer
root = new DefaultMutableTreeNode("Images");
tree = new JTree(root);
node1 = new DefaultMutableTreeNode("Rabbit");
node2 = new DefaultMutableTreeNode("Devastator");
root.add(node1);
root.add(node2);
tree.addTreeSelectionListener(new TreeSelectionListener()
{// 树节点选择动作
public void valueChanged(TreeSelectionEvent e)
{
Object obj = e.getPath().getLastPathComponent();
if (obj instanceof DefaultMutableTreeNode)
{
DefaultMutableTreeNode node = (DefaultMutableTreeNode)obj;
if (node == root)
file = "";// 选择根
if (node == node1)
file = "rabbit.jpg";// 选择node1
if (node == node2)
file = "devastator.gif";// 选择node2
sensor.setData(file);// 改变Observable
sensor.notifyObservers();// 通知observer，对象已改变
}
}
});
scroll = new JScrollPane(tree);
add(scroll, BorderLayout.CENTER);
}
public Observable getSensor()
{// 返回Observable对象，使Observer可以获取
return sensor;
}
}
class Sensor extends Observable
{// 定义自己的Observable
private Object data;
public void setData(Object newData)
{
data = newData;
setChanged();// 改变Observable
System.out.println("Data changed!");
}
public Object getData()
{
return data;
}
}
//RightPanel.java
package com.jungleford.test;
import java.awt.*;
import javax.swing.JPanel;
import java.util.Observer;
import java.util.Observable;
public class RightPanel extends JPanel implements Observer
{// 把图片浏览视图布局在右边
private Image image;
public void update(Observable subject, Object obj)
{// 定义接收到Observable变化后的响应动作
String file = (String)((Sensor)subject).getData();
if (!file.equals(""))
{
image = Toolkit.getDefaultToolkit().getImage(file);
MediaTracker tracker = new MediaTracker(this);// 定义图像跟踪
tracker.addImage(image, 0);
try
{
tracker.waitForID(0);// 等待图像的完全加载
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
else
image = null;
repaint();// 重绘组件
}
public void paintComponent(Graphics g)
{
g.setColor(Color.LIGHT_GRAY);
g.fillRect(0, 0, getWidth() - 1, getHeight() - 1);// 先将组件上的画面清除
if (image != null)
g.drawImage(image, 0, 0, this);// 绘制新的图像
}
}
//MainFrame.java
package com.jungleford.test;
import java.awt.*;
import javax.swing.JFrame;
public class MainFrame extends JFrame
{// 演示窗口
public static void main(String[] args)
{
MainFrame frame = new MainFrame();
RightPanel right = new RightPanel();
LeftPanel left = new LeftPanel(right);// 注册Observer
frame.getContentPane().add(left, BorderLayout.WEST);
frame.getContentPane().add(right, BorderLayout.CENTER);
frame.setTitle("Observer Test");
frame.setSize(400, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

1. 问题的提出

2. Observer模式

3. Java中的Observer模式：Observer和Observable

4. Observer模式在Java GUI事件模型中应用

5. 简单的例子

附录：Observer模式概览

参考资料：