原文：
http://javaeye.5d6d.com/thread-90-1-1.html
深入分析J2ME平臺MIDP低級事件處理機制
通常低級事件的處理是為了滿足游戲開發(fā)的需要，因為游戲開發(fā)相關(guān)的問題非常復(fù)雜。因此不在這里進行闡述，有興趣的朋友可以和我索要相關(guān)的游戲開發(fā)資料。MIDP定義了如下鍵值在Canvas類內(nèi)：
KEY_NUM0
KEY_NUM1
KEY_NUM2
KEY_NUM3
KEY_NUM4
KEY_NUM5
KEY_NUM6
KEY_NUM7
KEY_NUM8
KEY_NUM9
KEY_STAR
KEY_POUND
這些都是按鍵基本值，當(dāng)然有些手機是觸摸屏的。事件的傳遞是通過如下方法來實現(xiàn)的。
protected void keyPressed(int keyCode)
protected void keyReleased(int keyCode)
protected void keyRepeated(int keyCode)
protected void pointerPressed(int x, int y)
protected void pointerDragged(int x, int y)
protected void pointerReleased(int x, int y)
protected void showNotify()
protected void hideNotify()
protected abstract void paint(Graphics g)
commandAction() method of the CommandListener interface
開發(fā)者應(yīng)該繼承Canvas類的同時覆蓋相應(yīng)的方法來實現(xiàn)低級事件的處理，低級事件的處理是連續(xù)的、串行的，在前面的事件返回之前后面的事件不會執(zhí)行，
當(dāng)然也有例外，你可以參考API
doc得到答案。下面是一個例子，它的功能就是在屏幕上顯示出你按下鍵的鍵值，界面非常簡單因此沒有抓圖。代碼如下所示：
//LowLevelMIDlet.java
import javax.microedition.lcdui.Display;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
/*
* Created on 2004-6-24
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/
/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Style - Code Templates
*/
public class LowLevelMIDlet extends MIDlet
{
private Display display;
private KeyCanvas keyCanvas;
/*
* (non-Javadoc)
*
* @see javax.microedition.midlet.MIDlet#startApp()
*/
protected void startApp() throws MIDletStateChangeException
{
// TODO Auto-generated method stub
display = Display.getDisplay(this);
keyCanvas = new KeyCanvas();
display.setCurrent(keyCanvas);
}
/*
* (non-Javadoc)
*
* @see javax.microedition.midlet.MIDlet#pauseApp()
*/
protected void pauseApp()
{
// TODO Auto-generated method stub
}
/*
* (non-Javadoc)
*
* @see javax.microedition.midlet.MIDlet#destroyApp(boolean)
*/
protected void destroyApp(boolean arg0) throws MIDletStateChangeException
{
// TODO Auto-generated method stub
}
}
//KeyCanvas.java
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Graphics;
/*
* Created on 2004-6-25
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/
/**
* @author P2800
*
* TODO To change the template for this generated type comment go to Window -
* Preferences - Java - Code Style - Code Templates
*/
public class KeyCanvas extends Canvas implements CommandListener
{
private String key = "Press any key";
/*
* (non-Javadoc)
*
* @see javax.microedition.lcdui.Canvas#paint(javax.microedition.lcdui.Graphics)
*/
protected void paint(Graphics g)
{
// TODO Auto-generated method stub
g.setColor(255, 255, 255);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(0, 0, 0);
g.drawString(key, getWidth() / 2, getHeight() / 2, Graphics.TOP
| Graphics.HCENTER);
}
public void keyPressed(int keyCode)
{
key = keyCode + " is pressed";
repaint();
}
public void keyReleased(int keyCode)
{
key = keyCode + " is released";
repaint();
}
/*
* (non-Javadoc)
*
* @see javax.microedition.lcdui.CommandListener#commandAction(javax.microedition.lcdui.Command,
* javax.microedition.lcdui.Displayable)
*/
public void commandAction(Command arg0, Displayable arg1)
{
// TODO Auto-generated method stub
}
}