J2me中使用Canvas创建高级菜单总结

看了<<J2me中使用Canvas创建高级菜单>>后，将canvas创建高级菜单归结为两个问题：菜单的绘制和菜单事件的处理.设计了三个类：MenuMidlet，MenuScreen，Menu。
MenuMidlet是主类，该类继承了MIDlet类；
MenuScreen类负责事件处理；
Menu类负责菜单的绘制

2.菜单绘制
菜单有两种状态：激活状态和非激活状态.
在激活状态下，显示菜单项，并且可以接受用户的上下选择事件
在非激活状态下，隐藏菜单项，不接受用户的上下选择事件
菜单的绘制包括激活状态下的菜单绘制和非激活状态下的菜单绘制
非激活状态下的菜单绘制包括：左菜单(options)和右菜单(exit)绘制
激活状态下的菜单绘制包括：左菜单(options)和右菜单(cancel)绘制，左菜单项（新建，设定，记录，帮助，关于）绘制。如图：

3.菜单事件处理
Canvas提供了keyPressed(int key)来响应用户的按键 。
Canvas中的gameAction是将手机键盘映射成为游戏动作的机制。
需要响应UP，DOWN，FIRE，左菜单键，右菜单键事件
以下是源代码，在WTK2.5.2下编译通过

1)MenuMidlet类

import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
import javax.microedition.lcdui.*;
public class MenuMidlet extends MIDlet  {
    private   MenuScreen menuScreen;
    Display display;
 public MenuMidlet() {
  display= Display.getDisplay(this);
  menuScreen = new MenuScreen(this);
 }

 protected void startApp() throws MIDletStateChangeException {
 }

 protected void pauseApp() {
 }

 protected void destroyApp(boolean unconditional)
   throws MIDletStateChangeException {
 }
}

2）MenuScreen类

import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.GameCanvas;
import javax.microedition.media.*;
public class MenuScreen  extends GameCanvas {
 static int width; // screen width
 static int height; // screen height
 private int LEFT_SOFTKEY_CODE = -6;
 private int RIGHT_SOFTKEY_CODE = -7;
 // Menu Item Labels
 static final String[] menuOptions = { "新建", "设置",
   "记录", "帮助", "关于" };
 static int menuIdx;// 记录是在第几个菜单处按下的确定键。
 private int currentlySelectedIndex = 0;
 private boolean menuIsActive = false;
 private MenuMidlet midlet;
 private String leftOption;
 private String rightOption;
 private Graphics g;
 private Menu menu;

 // Constructor
 public MenuScreen(MenuMidlet midlet) {
  super(false);
  this.midlet = midlet;
  // Get Width and Height of Canvas
  width = getWidth();
  height = getHeight();
  setFullScreenMode(true);
  menuIdx = 0;
  g = getGraphics();
  leftOption = "Options";
  rightOption = "Exit";
  menu = new Menu(leftOption, rightOption, menuOptions);
  start();
  midlet.display.setCurrent(this);
 }

 public void start() {
  clearScreen();
  menu.drawInactiveMenu(this, g);
 }

 public void clearScreen() {
  g.setColor(0xffffff); // white
  g.fillRect(0, 0, width, height);
  flushGraphics();
 }
 
 protected void keyPressed(int keyCode) {
  if (menuIsActive) {
   if (keyCode == RIGHT_SOFTKEY_CODE) {
    // draw inactive menu again
    clearScreen();
    menu.drawInactiveMenu(this, g);
    menuIsActive = false;
   }
   keyCode = getGameAction(keyCode);
   if (keyCode == UP) {
    currentlySelectedIndex--;
    if (currentlySelectedIndex < 0) {
     currentlySelectedIndex = 0; // stay within limits
    }
    menu.drawActiveMenu(this, g, currentlySelectedIndex);
   }
   else if (keyCode == DOWN) {
    currentlySelectedIndex++;
    if (currentlySelectedIndex >= menuOptions.length) {
     currentlySelectedIndex = menuOptions.length - 1;
    }
    menu.drawActiveMenu(this, g, currentlySelectedIndex);
   }
   else if (keyCode == FIRE) {
    clearScreen();
    g.setColor(0x000000);
    g.drawString("[" + menuOptions[currentlySelectedIndex]
      + "] was selected", 10, 15, g.LEFT | g.TOP);
    menu.drawInactiveMenu(this, g);
    menuIsActive = false;
   }
  }
  else {
   if (keyCode == LEFT_SOFTKEY_CODE) { // "Options" pressed
    menu.drawActiveMenu(this, g, currentlySelectedIndex);
    menuIsActive = true;
   }
   else if (keyCode == RIGHT_SOFTKEY_CODE) {
    
   }
  }
 }
}

3）Menu类

import java.util.*;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
public class Menu {
 private String leftOption;
 private String rightOption;
 private String cancelOption = "Cancel";
 private String[] menuOptions;
 private int padding = 5;
 //颜色设置
 private static final int defaultFontColor = 0x000000; // 默认字体颜色
 private static final int selectedFontColor=0xfff000;  //选中后字体颜色
 private static final int bgColor = 0xCCCCCC;// 菜单背景色
 private static final int highLight=0x0000ff;//选中的菜单高亮显示颜色
 
 public Menu(String leftOption, String rightOption, String[] menuOptions) {
  this.leftOption = leftOption;
  this.rightOption = rightOption;
  this.menuOptions = menuOptions;
 } // end constructor

 public void drawInactiveMenu(GameCanvas canvas, Graphics g) {
  // create inactive menu font
  Font font = Font.getFont(Font.FACE_SYSTEM, Font.STYLE_BOLD,
    Font.SIZE_MEDIUM);
  int fontHeight = font.getHeight();
  // clear inactive menu background
  int width = canvas.getWidth();
  int height = canvas.getHeight();
  g.setColor(bgColor); // grey color
  g.fillRect(0, height - fontHeight - 2 * padding, width, height);
  // draw left and right menu options
  g.setFont(font);
  g.setColor(defaultFontColor); // black
  g.drawString(leftOption, padding, height - padding, g.LEFT | g.BOTTOM);
  g.drawString(rightOption, width - padding, height - padding, g.RIGHT
    | g.BOTTOM);
  canvas.flushGraphics();
 } // end drawInactiveMenu

 public void drawActiveMenu(GameCanvas canvas, Graphics g,
   int selectedOptionIndex) {
  Font font = Font.getFont(Font.FACE_SYSTEM, Font.STYLE_BOLD,
    Font.SIZE_MEDIUM);
  int fontHeight = font.getHeight();
  int width = canvas.getWidth();
  int height = canvas.getHeight();
  g.setColor(bgColor);
  g.fillRect(0, height - fontHeight - 2 * padding, width, height);
  // draw default menu bar options
  g.setFont(font);
  g.setColor(0x000000); // black
  g.drawString(leftOption, padding, height - padding, g.LEFT | g.BOTTOM);
  // draw "Cancel" option
  g.drawString(cancelOption, width - padding, height - padding, g.RIGHT
    | g.BOTTOM);
  canvas.flushGraphics();
  // draw menu options
  if (menuOptions != null) {
   //确定菜单的最大宽度、最大高度
   int menuMaxWidth = 0;
   int menuMaxHeight = 0;
   int currentWidth = 0;
   for (int i = 0; i < menuOptions.length; i++) {
    currentWidth = font.stringWidth(menuOptions[i]);
    if (currentWidth > menuMaxWidth) {
     menuMaxWidth = currentWidth;
    }
    menuMaxHeight += fontHeight + padding;
   }
   menuMaxWidth += 6 * padding;
   g.setColor(bgColor);
   g.fillRect(0, // x
     height - fontHeight - 2 * padding - menuMaxHeight, // y
     menuMaxWidth, menuMaxHeight);


   g.setFont(font);
   int menuOptionX = padding;
   int menuOptionY = height - fontHeight - 2 * padding - menuMaxHeight
     + padding;
    for(int i=0; i<=menuOptions.length; i++) {
     g.setColor(highLight);
     int lineOptionY= height-fontHeight - 2 * padding- menuMaxHeight+i*(fontHeight + padding);
              g.drawLine(0, lineOptionY,
                menuMaxWidth-1, lineOptionY);
          }
   for (int i = 0; i < menuOptions.length; i++) {
    if (i != selectedOptionIndex) {
     // draw unselected menu option
     g.setColor(defaultFontColor); // black
     g.drawString(menuOptions[i], menuOptionX, menuOptionY, g.LEFT
       | g.TOP);
    }
    else {
     // draw selected menu option
     g.setColor(highLight);
     int highOptionY=height - fontHeight - 2 * padding - menuMaxHeight+i*(fontHeight + padding);
     g.fillRect(0,highOptionY,menuMaxWidth,fontHeight + padding);
     g.setColor(selectedFontColor);
     g.drawString(menuOptions[i], menuOptionX, menuOptionY, g.LEFT
       | g.TOP);
     
    } 
    menuOptionY += padding + fontHeight;
   }
   canvas.flushGraphics();
  }
 }
}