JavaME 开发体会:线程编程解决手机地图按住方向键不放地图移动问题

JavaME 开发体会:线程编程解决手机地图按住方向键不放地图移动问题
 
初从 JavaEE 开发转入 JavaME 开发,线程编程技术越发显得重要.作者以一个真实项目中的体会,演示了线程编程在 JavaME 开发中的使用,可以巧妙地解决一些看似疑难的问题.
背景:以下代码是作者写的一个 JavaMe 手机地图移动的代码.
ImageMIDlet.java 源码如下:
/**
 * 文件名：ImageMIDlet.java
 *
 * 版本信息：
 * 日期：2009-10-17
 * Copyright XXX Corporation 2009 
 * 版权所有
 *
 */
package image.downed.move;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
/**
 * 
 * 项目名称：Imagedownedmove
 * 类名称：ImageMIDlet
 * 类描述：This is the main class of the image downed move.
 * 创建人：Defonds
 * 创建时间：2009-10-17 上午11:02:17
 * 修改人：Defonds
 * 修改时间：2009-10-17 上午11:02:17
 * 修改备注：
 * @version 
 * 
 */
public class ImageMIDlet extends MIDlet implements CommandListener
{
  /**
   * The canvas is the region of the screen.
   */
  ImageCanvas myCanvas;
  
  /**
   * The command objects appears as buttons.
   */
  private Command exitCommand = new Command("退出",Command.EXIT,99);
  
  /**
   * Initialize the canvas and the commands.
   */
  public ImageMIDlet()
  {
    myCanvas = new ImageCanvas(Display.getDisplay(this));
    myCanvas.addCommand(exitCommand);
    myCanvas.setCommandListener(this);
  }
  //-------------------------------------
 //Implimentation of MIDlet.
  
  /**
   * If the MIDlet was usring resources,it should release them in this method.
   */
  /* (non-Javadoc)
   * @see javax.microedition.midlet.MIDlet#destroyApp(boolean)
   */
  protected void destroyApp(boolean arg0) throws MIDletStateChangeException {}
  
  /**
   * This method is called to notify the MIDlet to enter a paused state.
   * The MIDlet should use this opportunity to release shared resources.
   */
  /* (non-Javadoc)
   * @see javax.microedition.midlet.MIDlet#pauseApp()
   */
  protected void pauseApp() { }
  /**
   * Start the application.
   */
  /* (non-Javadoc)
   * @see javax.microedition.midlet.MIDlet#startApp()
   */
  protected void startApp() throws MIDletStateChangeException
  {
    myCanvas.start();
  }
  //---------------------------------
 // implimentation of CommandListener.
  
  /**
   * Respond to a command issued on the Canvas.
   * (either reset or exit).
   */
  /* (non-Javadoc)
   * @see javax.microedition.lcdui.CommandListener#commandAction(javax.microedition.lcdui.Command, javax.microedition.lcdui.Displayable)
   */
  public void commandAction(Command arg0, Displayable arg1)
  {
   if(arg0 == exitCommand)
   {
     try
    {
      destroyApp(false);
      notifyDestroyed();
    } catch (MIDletStateChangeException e) {} 
   }
  }
}

ImageCanvas.java 源代码如下:
/**
 * 文件名：ImageCanvas.java
 *
 * 版本信息：
 * 日期：2009-10-17
 * Copyright XXX Corporation 2009 
 * 版权所有
 *
 */
package image.downed.move;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;
/**
 * 
 * 项目名称：Imagedownedmove
 * 类名称：ImageCanvas
 * 类描述：This class represents the region of the screen.
 * 实现按住向下键不放,N 张图片一起下移的算法.
 * 创建人：Defonds
 * 创建时间：2009-10-17 上午11:32:14
 * 修改人：Defonds
 * 修改时间：2009-10-17 上午11:32:14
 * 修改备注：
 * @version 
 * 
 */
public class ImageCanvas extends Canvas
{
  //-------------------------------
  //fields
  /**
   * A handle to the screen of the device.
   */
  Display myDisplay;
  
  /**
   *  每按一下向下键，图片向上移动的距离
   */
  private final int distance = 5;
  
  /**
   *  每按一下向下键，还有多少距离显示空白
   */
  private int ydown = 0;
  
  /**
   *  手机屏幕中心点坐标
   */
  private final int x = getWidth()/2,y = getHeight()/2;
  
  /**
   *  下载图片的宽度
   */
  private final int imageWidth = 300;
  
  /**
   *  判断是否显示第5，6张，停止显示第1，2张
   */
  boolean showNew = false;
  
  /**
   *  6个图片的初始坐标
   */
  private int x1 = x - imageWidth,y1 = y - imageWidth;
  private int x2 = x,y2 = y - imageWidth;
  private int x3 = x - imageWidth,y3 = y;
  private int x4 = x,y4 = y;
  private int x5 = x - imageWidth,y5 = getHeight() - 1;
  private int x6 = x,y6 = getHeight() - 1;
  /**
   * 要画的图片
   */
  Image image1,image2,image3,image4,image5,image6;
  
  /**
   *  要下载的图片的URL(规格：全部是 300 X 300)
   */
  String url1 ="http://img1.mapbar.com/maplite/mapbank/baidu/8/116_39/4_7.png"; 
  String url2 ="http://img3.mapbar.com/maplite/mapbank/baidu/8/116_39/5_7.png"; 
  String url3 ="http://img.mapbar.com/maplite/mapbank/baidu/8/116_39/6_6.png"; 
  String url4 ="http://mappng.baidu.com/maplite/mapbank/baidu/5/11_4/3_3.png"; 
  String url5 = "http://img3.mapbar.com/maplite/mapbank/baidu/8/109_42/1_1.png";
  String url6 = "http://www.sunyn.com/kmtour/UploadFiles_7357/200706/20070625215831613.png";
      
  /**
   *  要下载图片的字节流
   */
  byte[] byteofimg1,byteofimg2,byteofimg3,byteofimg4,byteofimg5,byteofimg6;  
  
  //-------------------------
  //Initialization
  /**
   * Constructor merely sets the display.
   */
 public ImageCanvas(Display d)
  {
   super();
   myDisplay = d;
   ydown = imageWidth - getHeight()/2;
   try 
   {
       byteofimg1 = loadHttpFile(url1);
       System.out.println("byteofimg1.length="+byteofimg1.length);
       byteofimg2 = loadHttpFile(url2);
       System.out.println("byteofimg2.length="+byteofimg2.length);
       byteofimg3 = loadHttpFile(url3);
       System.out.println("byteofimg3.length="+byteofimg3.length);
       byteofimg4 = loadHttpFile(url4);
       System.out.println("byteofimg4.length="+byteofimg4.length);
   } 
   catch (IOException e) 
   {
       e.printStackTrace();
   }
}
  
 /**
  * This is called as soon as the application begins.
  */
 void start() 
 {
   myDisplay.setCurrent(this);
   repaint();
 }
 
 /**
  *     清屏
  */
 public void clearScreen(Graphics g)
 {
   //g.setColor(0, 0, 0);//要设置的底色-黑色
   g.setColor(255,255,255);   //要设置的底色-白色
   g.fillRect(0, 0, this.getWidth(), this.getHeight());
}
 
 /**
  *     键盘事件的重写
  */
 protected void keyPressed(int keyCode) 
 {
   ydown = ydown - distance;
   //如果出现空白，停止显示第1，2张图片，开始显示3，4以及5,6
   if(ydown < 0) 
   {
       try 
       {
           byteofimg5 = loadHttpFile(url5);
       } 
       catch (IOException e) 
       {
           e.printStackTrace();
       }
       System.out.println("byteofimg5.length="+byteofimg5.length);
       try 
       {
           byteofimg6 = loadHttpFile(url6);
       } catch (IOException e) 
       {
           e.printStackTrace();
       }
       System.out.println("byteofimg6.length="+byteofimg6.length);
       showNew = !showNew;
       //ydown重置
       ydown = imageWidth;
       System.out.println("byteofimg2.length="+byteofimg2.length);
   }
   int action = getGameAction(keyCode);
   switch(action) 
   {
   case Canvas.DOWN:
       y1 = y1 - distance;
       y2 = y2 - distance;
       y3 = y3 - distance;
       y4 = y4 - distance;
       if(showNew) 
       {
           y5 = y5 - distance;
           y6 = y6 - distance;
       }
       repaint();
   }
}
 /**
  *     下载图片函数
  */
 public byte[] loadHttpFile(String url) throws IOException 
 { 
   byte[] byteBuffer; 
   HttpConnection hc = (HttpConnection) Connector.open(url); 
   System.out.println("loadHttpFile:"+url);
   try 
   { 
       hc.setRequestMethod(HttpConnection.GET); 
       InputStream is = hc.openInputStream(); 
       try 
       { 
           int len = (int) hc.getLength(); 
           if (len > 0) 
           { 
               byteBuffer = new byte[len]; 
               int done = 0; 
               while (done < len) 
               { 
                   done += is.read(byteBuffer, done, len - done); 
               } 
           } else 
           { 
               ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
               byte[] buffer = new byte[512]; 
               int count; 
               while ( (count = is.read(buffer)) >= 0 ) 
               { 
                   bos.write(buffer, 0, count); 
               } 
               byteBuffer = bos.toByteArray(); 
           } 
       } finally 
       { 
           is.close(); 
       } 
   } finally 
   { 
       hc.close(); 
   } 
    
   return byteBuffer; 
} 
 
 //-------------------------------------------
 //Graphics methods
 
 /**
  * Clear the screen and display the image.
  */
 
  /* (non-Javadoc)
   * @see javax.microedition.lcdui.Canvas#paint(javax.microedition.lcdui.Graphics)
   */
 protected void paint(Graphics arg0) 
 {
     clearScreen(arg0);
     if(!showNew) 
     {
         image1 = Image.createImage(byteofimg1,0, byteofimg1.length);
         image2 = Image.createImage(byteofimg2,0, byteofimg2.length);
         image3 = Image.createImage(byteofimg3,0, byteofimg3.length);
         image4 = Image.createImage(byteofimg4,0, byteofimg4.length);
         arg0.drawImage(image1, x1, y1, Graphics.TOP|Graphics.LEFT);
         arg0.drawImage(image2, x2, y2, Graphics.TOP|Graphics.LEFT);
         arg0.drawImage(image3, x3, y3, Graphics.TOP|Graphics.LEFT);
         arg0.drawImage(image4, x4, y4, Graphics.TOP|Graphics.LEFT);
     }
     else 
     {
         image3 = Image.createImage(byteofimg3,0, byteofimg3.length);
         image4 = Image.createImage(byteofimg4,0, byteofimg4.length);
         image5 = Image.createImage(byteofimg5,0, byteofimg5.length);
         image6 = Image.createImage(byteofimg6,0, byteofimg6.length);
         arg0.drawImage(image3, x3, y3, Graphics.TOP|Graphics.LEFT);
         arg0.drawImage(image4, x4, y4, Graphics.TOP|Graphics.LEFT);
         arg0.drawImage(image3, x5, y5, Graphics.TOP|Graphics.LEFT);
         arg0.drawImage(image4, x6, y6, Graphics.TOP|Graphics.LEFT);
     }
 }
}


这段代码解决了:手机地图下载,手机地图随方向键的按下而移动.但是还是存在问题:如果用户只按一下方向键,地图移动 5 个象素,而按住住方向键不放同样也是移动 5 个象素.对于这种效果,用户肯定是不会满意的.然而按键事件只是通知按下和松开,仅仅改写按键事件方法,不能起到根据用户按键不放时间进行移动地图的效果.这个时间段怎么计算呢?作者想到了线程编程,问题迎刃而解.解决后的源码如下,读者可以把代码考到自己电脑上,运行一下,体会其中的奥妙.
ImageMIDlet.java 源码如下:
/**
 * 文件名：ImageMIDlet.java
 *
 * 版本信息：
 * 日期：2009-10-17
 * Copyright XXX Corporation 2009 
 * 版权所有
 *
 */
package image.downed.move;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
/**
 * 
 * 项目名称：Imagedownedmove
 * 类名称：ImageMIDlet
 * 类描述：This is the main class of the image downed move.
 * 创建人：Defonds
 * 创建时间：2009-10-17 上午11:02:17
 * 修改人：Defonds
 * 修改时间：2009-10-17 上午11:02:17
 * 修改备注：
 * @version 
 * 
 */
public class ImageMIDlet extends MIDlet implements CommandListener
{
  /**
   * The canvas is the region of the screen.
   */
  ImageCanvas3 myCanvas;
  
  /**
   * The command objects appears as buttons.
   */
  private Command exitCommand = new Command("退出",Command.EXIT,99);
  
  /**
   * Initialize the canvas and the commands.
   */
  public ImageMIDlet()
  {
    myCanvas = new ImageCanvas3(Display.getDisplay(this));
    myCanvas.addCommand(exitCommand);
    myCanvas.setCommandListener(this);
  }
  //-------------------------------------
 //Implimentation of MIDlet.
  
  /**
   * If the MIDlet was usring resources,it should release them in this method.
   */
  /* (non-Javadoc)
   * @see javax.microedition.midlet.MIDlet#destroyApp(boolean)
   */
  protected void destroyApp(boolean arg0) throws MIDletStateChangeException {}
  
  /**
   * This method is called to notify the MIDlet to enter a paused state.
   * The MIDlet should use this opportunity to release shared resources.
   */
  /* (non-Javadoc)
   * @see javax.microedition.midlet.MIDlet#pauseApp()
   */
  protected void pauseApp() { }
  /**
   * Start the application.
   */
  /* (non-Javadoc)
   * @see javax.microedition.midlet.MIDlet#startApp()
   */
  protected void startApp() throws MIDletStateChangeException
  {
    myCanvas.start();
  }
  //---------------------------------
 // implimentation of CommandListener.
  
  /**
   * Respond to a command issued on the Canvas.
   * (either reset or exit).
   */
  /* (non-Javadoc)
   * @see javax.microedition.lcdui.CommandListener#commandAction(javax.microedition.lcdui.Command, javax.microedition.lcdui.Displayable)
   */
  public void commandAction(Command arg0, Displayable arg1)
  {
   if(arg0 == exitCommand)
   {
     try
    {
      destroyApp(false);
      notifyDestroyed();
    } catch (MIDletStateChangeException e) {} 
   }
  }
}

ImageCanvas3.java 源代码如下:
/**
 * 文件名：ImageCanvas3.java
 *
 * 版本信息：
 * 日期：2009-10-18
 * Copyright XXX Corporation 2009 
 * 版权所有
 *
 */
package image.downed.move;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Date;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;
/**
 * 
 * 项目名称：Imagedownedmove
 * 类名称：ImageCanvas3
 * 类描述：This class represents the region of the screen.
 * 利用 按键方法重写 + 线程  + 计时器  解决按住向下键不放手机地图移动的距离问题.
 * 创建人：Defonds
 * 创建时间：2009-10-18 上午10:33:03
 * 修改人：Defonds
 * 修改时间：2009-10-18 上午10:33:03
 * 修改备注：
 * @version 
 * 
 */
public class ImageCanvas3 extends Canvas implements Runnable
{
  //----------------------------
  //fields
  
  /**
   * A handle to the screen of the device.
   */
  Display myDisplay;
  
  /**
   * A handle to the run method.
   */
  private Thread myThread = null;
  
  /**
   *    按住向下建的单位时间内,图片向上移动的距离.
   */
  private final int yspeed = 5;
  
  /**
   *    手机屏幕中心点坐标.
   */
  private final int x = getWidth()/2,y = getHeight()/2;
  
  /**
   *    下载图片的宽度(假想全部为正方形图片).
   */
  private final int imageWidth = 300;
  
  /**
   *    按键处理代码需要变量:
   *    keyDown:Canvas.DOWN 按下为 true,反之为 false;
   *    action:GameAction
   */
  private boolean keyDown = false;
  private int action = 0;
  
  /**
   *  6 个图片的初始坐标.
   */
  private int x1 = x - imageWidth,y1 = y - imageWidth;
  private int x2 = x,y2 = y - imageWidth;
  private int x3 = x - imageWidth,y3 = y;
  private int x4 = x,y4 = y;
  private int x5 = x - imageWidth,y5 = y + imageWidth;
  private int x6 = x,y6 = y + imageWidth;
  
  /**
   *    要画的图片.
   */
  Image image1,image2,image3,image4,image5,image6;
  
  /**
   *     要下载的图片的 URL(规格: 300 X 300).
   */
  String url1 = "http://img1.mapbar.com/maplite/mapbank/baidu/8/116_39/4_7.png";
  String url2 = "http://img3.mapbar.com/maplite/mapbank/baidu/8/116_39/5_7.png";
  String url3 = "http://img.mapbar.com/maplite/mapbank/baidu/8/116_39/6_6.png";
  String url4 = "http://mappng.baidu.com/maplite/mapbank/baidu/5/11_4/3_3.png";
  String url5 = "http://img3.mapbar.com/maplite/mapbank/baidu/8/109_42/1_1.png";
  String url6 = "http://www.sunyn.com/kmtour/UploadFiles_7357/200706/20070625215831613.png";
  
  /**
   *    要下载的图片的字节流.
   */
  byte[] byteofimg1,byteofimg2,byteofimg3,byteofimg4,byteofimg5,byteofimg6,byteofimg7;
  
  //---------------------------------------
  //Initialization.
  /**
   * Constructor merely sets the display.
   */
  public ImageCanvas3(Display d)
  {
    super();
    myDisplay = d;
    try
    {
      byteofimg1 = loadHttpFile(url1);
      System.out.println("byteofimg1.length="+byteofimg1.length);
      byteofimg2 = loadHttpFile(url2);
      System.out.println("byteofimg2.length="+byteofimg2.length);
      byteofimg3 = loadHttpFile(url3);
      System.out.println("byteofimg3.length="+byteofimg3.length);
      byteofimg4 = loadHttpFile(url4);
      System.out.println("byteofimg4.length="+byteofimg4.length);
      byteofimg5 = loadHttpFile(url5);
      System.out.println("byteofimg5.length="+byteofimg5.length);
      byteofimg6 = loadHttpFile(url6);
      System.out.println("byteofimg6.length="+byteofimg6.length);
    }
    catch (IOException e) 
    {
      e.printStackTrace();
    }
  }
  
  /**
   * This is called as soon as the application begins.
   */
  public void start() 
  {
    if(myThread == null) 
    {
      myThread = new Thread(this);
      myThread.start();
    }
    myDisplay.setCurrent(this);
    repaint();
  }
  
  /**
   * This is called as soon as the application ends.
   */
  public void stop()
  {
    if(myThread != null)
    {
      myThread = null;
    }
  }
  
  /**
   *    清屏.
   */
  public void clearScreen(Graphics g)
  {
    g.setColor(255,255,255);//要设置的底色:白色
    g.fillRect(0, 0, getWidth(), getHeight());
  }
  
  /**
   *    键盘事件函数 keyPressed 的重写
   */
  protected void keyPressed(int keyCode) 
  {
    action = getGameAction(keyCode);
    switch(action)
    {
    case Canvas.DOWN:keyDown = true;
    }
  }
  
  /**
   *    键盘事件函数 keyReleased 的重写
   */
  protected void keyReleased(int keyCode)
  {
    action = getGameAction(keyCode);
    switch(action)
    {
    case Canvas.DOWN:
      keyDown = false;//keyDown 复位.
    }
  }
  
  /**
   *    http 下载图片函数.
   */
  public byte[] loadHttpFile(String url) throws IOException 
  { 
    byte[] byteBuffer; 
    HttpConnection hc = (HttpConnection) Connector.open(url); 
    System.out.println("loadHttpFile:"+url);
    try 
    { 
        hc.setRequestMethod(HttpConnection.GET); 
        InputStream is = hc.openInputStream(); 
        try 
        { 
            int len = (int) hc.getLength(); 
            if (len > 0) 
            { 
                byteBuffer = new byte[len]; 
                int done = 0; 
                while (done < len) 
                { 
                    done += is.read(byteBuffer, done, len - done); 
                } 
            } else 
            { 
                ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
                byte[] buffer = new byte[512]; 
                int count; 
                while ( (count = is.read(buffer)) >= 0 ) 
                { 
                    bos.write(buffer, 0, count); 
                } 
                byteBuffer = bos.toByteArray(); 
            } 
        } finally 
        { 
            is.close(); 
        } 
    } finally 
    { 
        hc.close(); 
    } 
     
    return byteBuffer; 
 } 
  
//-----------------------
  //Graphics method.
  
  /**
   * Clear the screen and display the image.
   */
  /* (non-Javadoc)
   * @see javax.microedition.lcdui.Canvas#paint(javax.microedition.lcdui.Graphics)
   */
  protected void paint(Graphics arg0)
  {
    clearScreen(arg0);
    image1 = Image.createImage(byteofimg1,0, byteofimg1.length);
    image2 = Image.createImage(byteofimg2,0, byteofimg2.length);
    image3 = Image.createImage(byteofimg3,0, byteofimg3.length);
    image4 = Image.createImage(byteofimg4,0, byteofimg4.length);
    image5 = Image.createImage(byteofimg5,0, byteofimg5.length);
    image6 = Image.createImage(byteofimg6,0, byteofimg6.length);
    arg0.drawImage(image1, x1, y1, Graphics.TOP|Graphics.LEFT);
    arg0.drawImage(image2, x2, y2, Graphics.TOP|Graphics.LEFT);
    arg0.drawImage(image3, x3, y3, Graphics.TOP|Graphics.LEFT);
    arg0.drawImage(image4, x4, y4, Graphics.TOP|Graphics.LEFT);
    arg0.drawImage(image5, x5, y5, Graphics.TOP|Graphics.LEFT);
    arg0.drawImage(image6, x6, y6, Graphics.TOP|Graphics.LEFT);
  }
//---------------------------------
//implimentation of Runnable.
  
  /* (non-Javadoc)
   * @see java.lang.Runnable#run()
   */
  public void run()
  {
    while(true)
    {
      if(keyDown)
      {
        try
        {
          Thread.sleep(200);
        } catch (InterruptedException e)
        {
          e.printStackTrace();
        }
        System.out.println("向下键被按下,屏幕开始重绘!");
        y1 = y1 - yspeed;
        y2 = y2 - yspeed;
        y3 = y3 - yspeed;
        y4 = y4 - yspeed;
        y5 = y5 - yspeed;
        y6 = y6 - yspeed;
        repaint();
      }
    }
  }
}