二、实现游戏的步骤

　　下图显示的是一个游戏MIDlet在成功安装和运行之后用户界面状态的典型的变化流程。我们想通过一个游戏者的视角来阐述开发移动游戏的过程。


图3 用户界面状态图表

　　1 开始游戏

　　在用户启动MIDlet之后，将显示游戏特定的闪动屏幕。闪动屏幕是FullCanvas的一个实例。它可用于显示一个公司的标志或者用动画形式介绍游戏。除了End键以外的所有键盘事件（MIDlet可用的）都可以跳过闪动屏幕并显示主菜单。还应该设置一个时间限定，能够在一定的时间过后自动跳出闪动屏幕进入游戏屏幕。
GameMIDlet类是游戏的基本类；它处理MIDlet的生命周期并且处理游戏显示。下面的代码是闪动屏幕和游戏MIDlet类的构架。

//Skeleton for the base class of game
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class GameMIDlet extends MIDlet {
　private Display display = null;
　//Splash screen that starts the application
　private SplashFullCanvas splash;
　public GameMIDlet() {
　　splash = new SplashFullCanvas(this);
　}
　protected void startApp() throws MIDletStateChangeException {
　　if (display == null) {
　　　display = Display.getDisplay(this);
　　}
　　//splash screen to the display
　　setDisplayable(splash);
　}
　protected void pauseApp() {
}

　protected void destroyApp(boolean p0)
　throws MIDletStateChangeException {
　}

　public void setDisplayable(Displayable dl) {
　　display.setCurrent(dl);
　}
}

//Skeleton for the splash screen in Nokia Java Game
import javax.microedition.lcdui.*;
import java.util.Timer;
import java.util.TimerTask;
import com.nokia.mid.ui.*;

public class SplashFullCanvas extends FullCanvas {
　private GameMIDlet parent = null;
　private MainMenu menu = null;
　private Timer timer = null;
　public SplashFullCanvas(GameMIDlet parent) {
　　this.parent = parent;
　　menu = new MainMenu(
　　　Resources.getString(Resources.ID_GAME_NAME),
　　　List.IMPLICIT, parent);
　　　startTimer();
　}
protected void paint(Graphics g) {
　//Do the splash screen here
}
protected void keyPressed(int keyCode) {
　timer.cancel();
　timer = null;
　//All key events received set the main menu to the screen
　parent.setDisplayable(menu);
}

//Timer for the splash screen. Main menu is set to the display
//after 5 seconds.
private void startTimer() {
　TimerTask task =new TimerTask() {
　　public void run() {
　　　parent.setDisplayable(menu);
　　}
　};
　timer = new Timer();
　timer.schedule(task, 5000);
}
}

　　2 主菜单（MainMenu）屏幕

　　主菜单是包含游戏特定选项的固有目录（"Continue"、"New game"、"Options"、"High scores"、"Instructions"、"About"和"Exit game"）。"Continue"只有在游戏被暂停的时候才能被显示。当"Continue"显示的时候，它必须是目录列表的第一个元素。主菜单的标题必须是游戏的名称。下面的代码是主菜单的框架。

//Skeleton for the main menu
import javax.microedition.lcdui.*;
public class MainMenu extends List implements CommandListener {
　private GameMIDlet parent = null;
　private GameFullCanvas game = null;
　public MainMenu(String p0, int p1, String[] p2, Image[] p3,
　GameMIDlet parent) {
　　super(p0, p1, p2, p3);
　　init(parent);
　}
　public MainMenu(String p0, int p1, GameMIDlet parent) {
　　super(p0, p1);
　　init(parent);
　}
　public void init(GameMIDlet parent) {
　　this.parent = parent;
　　this.setCommandListener(this);
　　//if game paused then "Continue" should be available in
　　//selection list
　　if (game != null && game.isPaused()) {
　　　if(!(this.getString(0).equals(
　　　　new String(Resources.getString(
　　　　　Resources.ID_GAME_CONTINUE))))) {
　　　　　　this.insert(0,
　　　　　　　Resources.getString(Resources.ID_GAME_CONTINUE),
　　　　　　　null);
　　　　　}
　　　　　this.setSelectedIndex(0,true);
　　　　}
　　　else {
　　　　//These must be with or without icons
　　　　this.append(Resources.getString(Resources.ID_GAME_NEW), null);
　　　　this.append(Resources.getString(Resources.ID_GAME_OPTIONS),null);
　　　　this.append(Resources.getString(
　　　　　Resources.ID_GAME_HIGHSCORES), null);
　　　　this.append(Resources.getString(
　　　　Resources.ID_GAME_INSTRUCTIONS), null);
　　　　this.append(Resources.getString(Resources.ID_GAME_ABOUT), null);
　　　　this.append(Resources.getString(Resources.ID_GAME_EXIT), null);
　　　}
　　}
　　public void commandAction(Command p0, Displayable p1) {
　　　List lis = (List) p1;
　　　String selected =
　　　lis.getString(lis.getSelectedIndex());
　　　if (selected.equals(Resources.getString(Resources.ID_GAME_NEW))) {
　　　　game = new GameFullCanvas(parent, this);
　　　　parent.setDisplayable(game);
　　　}
　　　else if (selected.equals(
　　　　Resources.getString(Resources.ID_GAME_OPTIONS))) {
　　　　　parent.setDisplayable(
　　　　　　new OptionList(Resources.getString(Resources.ID_GAME_OPTIONS),
　　　　　　　List.IMPLICIT,
　　　　　　　parent, this));
　　　　}
　　　else if (selected.equals(
　　　　Resources.getString(Resources.ID_GAME_HIGHSCORES))) {
　　　　　parent.setDisplayable(new HighScore(parent, this));
　　　　}
　　　else if (selected.equals(
　　　　Resources.getString(Resources.ID_GAME_INSTRUCTIONS))) {
　　　　　parent.setDisplayable(
　　　　　　new Instructions(
　　　　　　　Resources.getString(Resources.ID_GAME_INSTRUCTIONS),parent,this));
　　　　}
　　　else if (selected.equals(
　　　　Resources.getString(Resources.ID_GAME_ABOUT))) {
　　　　　parent.setDisplayable(
　　　　　　new About(
　　　　　　　Resources.getString(Resources.ID_GAME_ABOUT),
　　　　　　　parent,
　　　　　　　this));
　　　　}
　　　else if (selected.equals(
　　　　Resources.getString(Resources.ID_GAME_EXIT))) {
　　　　　parent.notifyDestroyed();
　　　}
　　　else if (selected.equals(
　　　　Resources.getString(Resources.ID_GAME_CONTINUE))) {
　　　　　if (game != null) {
　　　　　　game.gameContinue();
　　　　　　parent.setDisplayable(game);
　　　}
　　}
　}
}

3 游戏屏幕

　　如果用户从主菜单中选择"New game"，那么开始游戏并且显示游戏屏幕。游戏屏幕使用全屏画布（FullCanvas）。如果按下任何功能键，那么用户界面必须返回主菜单，并且应使游戏暂停。其他的按键对游戏是有效的。注意：游戏不应该在屏幕上创建任何功能键的标签。如果必须使用功能键标签，那么应用程序应该使用默认的Canvas屏幕Commands。示例代码没有解决诸如线程和线程安全等问题，这些问题在设计的时候必须格外注意。下面的代码是游戏屏幕的框架。

import javax.microedition.lcdui.*;
import com.nokia.mid.ui.*;
public class GameFullCanvas extends FullCanvas {
private GameMIDlet parent = null;
private MainMenu menu = null;
private boolean gamePaused = false;
public GameFullCanvas(GameMIDlet parent, MainMenu menu) {
this.parent = parent;
this.menu = menu;
}
protected void paint(Graphics g) {
//Paint the game screen here
}
protected void keyPressed(int keyCode) {
if (keyCode == KEY_SOFTKEY1 || keyCode == KEY_SOFTKEY2
|| keyCode == KEY_SOFTKEY3) {
gamePaused = true;
//main menu to the screen
menu.init(parent);
parent.setDisplayable(menu);
}
}
public void gameContinue() {
gamePaused = false;
}
public boolean isPaused() {
return gamePaused;
}
}

　　4 游戏选项屏幕

　　用户可以通过选择主菜单中的"Options"选项改变特定的游戏选项。Options列表是固有的列表，包含处理游戏设置的条目，例如：声音、振动（见一、8节）、音调等等。如果要回到主菜单的话，需要使用Back命令。下面的代码是Options列表的框架。

　　注意：如果游戏被安装到Games菜单的话，就不需要lights/sounds设置条目了，因为那些选项已经由Games菜单提供了。

import javax.microedition.lcdui.*;
public class OptionList extends List implements CommandListener {
private GameMIDlet parent = null;
private MainMenu menu = null;
private KeyDefinitions def = null;
private Command back = new Command("", Command.BACK, 2);
public OptionList(String p0, int p1, String[] p2, Image[] p3,
GameMIDlet parent, MainMenu menu) {
super(p0, p1, p2, p3);
this.menu = menu;
init(parent);
}
public OptionList(String p0, int p1, GameMIDlet parent,
MainMenu menu) {
super(p0, p1);
this.menu = menu;
init(parent);
}
private void init(GameMIDlet parent) {
this.parent = parent;
this.addCommand(back);
this.setCommandListener(this);
//These are just a examples for the game specific options
this.append(Resources.getString(Resources.ID_GAME_LEVEL),
null);
this.append(Resources.getString(Resources.ID_GAME_SOUNDS),
null);
this.append(Resources.getString(Resources.ID_GAME_VIBRA),
null);
}
public void commandAction(Command p0, Displayable p1) {
if (p0 == back) {
parent.setDisplayable(menu);
}
else {
List lis = (List) p1;
int idx = lis.getSelectedIndex();
switch (idx) {
case 0:
//TODO
break;
case 1:
//TODO
break;
case 2:
//TODO
break;
case 3:
parent.setDisplayable(def);
break;
//More if needed
default:
break;
}
}
}
}

5 高分屏幕

　　当用户从主菜单中选择"High scores"选项的时候，高分就会显示出来。高分是显示在全屏画布（FullCanvas）实例上的。分数应该在一个屏幕上就显示完，而不要卷动页面，因为这样会给用户带来麻烦。
当然了，高分屏幕也可能会包含一些图片或者动画。用户应该能够通过按下左功能键、右功能键、数字键或者Send键返回主菜单。这个例子不提供任何处理高分的机制。处理高分的两种典型的方法是通过使用记录管理服务（RMS）永久保存分数或者通过HTTP连接把高分保存到服务器中。下面的代码是高分的框架。

import javax.microedition.lcdui.*;
import com.nokia.mid.ui.*;
public class HighScore extends FullCanvas {
private GameMIDlet parent = null;
private MainMenu menu = null;
public HighScore(GameMIDlet parent, MainMenu menu) {
this.parent = parent;
this.menu = menu;
}
protected void paint(Graphics g) {
//Paint the high scores here
}
public void keyPressed(int keyCode) {
if (keyCode != KEY_END) {
//selection list to the screen
parent.setDisplayable(menu);
}
}
}

　　6 教学屏幕

　　当用户从主菜单中选择"Instructions"条目的时候，就会显示出游戏的规则。游戏规则文本放置在Form实例中。Form中应该包含用于进入下一条教学规则的命令（例如，标签"More"）和回到主菜单的命令（例如，标签"Back"）。"More"一般由左功能键控制，而"Back"由右功能键控制。如果教学规则里包含动画，那么这些动画应该使用全屏画布（FullCanvas）来显示。按下左功能键将跳过动画进入下一个教学屏幕。按下右功能键，用户将从动画中回到主菜单。键End将结束应用程序。下面的代码是文字教学规则和动画的框架。

//Text instructions. Text can be written in constructor or in own
method.
//Developer should remember that also instruction texts should be
//internationalized
import javax.microedition.lcdui.*;
public class Instructions extends Form implements CommandListener {
//Command for going next instruction if needed
private Command more = new Command(
Resources.getString(Resources.ID_GAME_MORE),
Command.OK, 1);
//Command for going back to the main menu
private Command back = new Command("", Command.BACK, 2);
private GameMIDlet parent = null;
private MainMenu menu = null;
public Instructions(String title, GameMIDlet parent, MainMenu
menu) {
super(title);
this.parent = parent;
this.menu = menu;
this.addCommand(back);
this.addCommand(more);
this.setCommandListener(this);
}
public void commandAction(Command p0, Displayable p1) {
if (p0 == more) {
//go to the next if needed e.g animation
parent.setDisplayable(new InstructionAnimation(parent));
}
else if (p0 == back) {
parent.setDisplayable(menu);
}
}
}
//Instruction animation
import javax.microedition.lcdui.*;
import com.nokia.mid.ui.*;
public class InstructionAnimation extends FullCanvas {
private GameMIDlet parent = null;
public InstructionAnimation(GameMIDlet parent) {
this.parent = parent;
}
protected void paint(Graphics g) {
//Do the animation here
}
public void keyPressed(int keyCode) {
if (keyCode == KEY_SOFTKEY1) {
//go to the next instruction screen if needed
}
else if (keyCode == KEY_SOFTKEY2) {
//selection list to the screen
parent.setDisplayable(new MainMenu(
Resources.getString (
Resources.ID_GAME_NAME),
List.IMPLICIT, parent));
}
}
}

　　7关于（About）屏幕

　　关于（About）屏幕显示游戏制作公司的消息文本或标志。当用户从主菜单中选择"About"选项的时候，就会启动这个屏幕。和教学规则页面一样，关于屏幕页面如果只需要文本信息的话，那么可以使用Form来实现。如果需要图像或动画，那么应该使用Canvas或FullCanvas。

//Text "About" code skeleton
import javax.microedition.lcdui.*;
public class About extends Form implements CommandListener {
//Command for going back to the main menu
private Command back = new Command("", Command.BACK, 1);
private GameMIDlet parent = null;
private MainMenu menu = null;
public About(String title, GameMIDlet parent, MainMenu menu) {
super(title);
this.parent = parent;
this.menu = menu;
this.addCommand(back);
this.setCommandListener(this);
}
public void commandAction(Command p0, Displayable p1) {
if (p0 == back) {
parent.setDisplayable(menu);
}
}
}

　　8 退出

　　从主菜单中选择"Exit game"选项来中止游戏并释放所有的资源。

　　9 Resources类

　　Resources类不是一个用户界面类，与本文中介绍的其他类不同。这个类处理国际化问题。

/**
* A simple class to simulate a resource bundle.
* Modify the contents of this class according to the
* locales/languages you want your application to support.
* In your application, retrieve a string using code such as the
* following:
*

* String s = Resources.getString(Resources.ID_GAME_NEW);
* 

* Copyright (C) 2002 Nokia Corporation
*/
public class Resources {
// Identifiers for text strings.
public static final int ID_GAME_NEW = 0;
public static final int ID_GAME_OPTIONS = 1;
public static final int ID_GAME_HIGHSCORES = 2;
public static final int ID_GAME_INSTRUCTIONS = 3;
public static final int ID_GAME_ABOUT = 4;
public static final int ID_GAME_CONTINUE = 5;
public static final int ID_GAME_BACK = 6;
public static final int ID_GAME_MORE = 7;
public static final int ID_GAME_EXIT = 8;
public static final int ID_GAME_LEVEL = 9;
public static final int ID_GAME_SOUNDS = 10;
public static final int ID_GAME_VIBRA = 11;
public static final int ID_GAME_NAME = 12;
// List of supported locales.
// The strings are Nokia-specific values
// of the "microedition.locale" system property.
private static final String[] supportedLocales = {
"en", "fi-FI", "fr", "de"
};
//NOTE: default language must be the first one
//for getString to work!
// Strings for each locale, indexed according to the
// contents of supportedLocales
private static final String[][] strings = {
{ "New game", "Settings", "High scores", "Instructions",
"About","Continue", "Back", "More", "Exit game",
"Level", "Sounds","Shakes", "Game name" },
{ "Uusi peli", "Asetukset", "Huipputulokset", "Peliohjeet",
"Tietoja","Jatka", "Poistu", "Jatka", "Poistu",
"Vaikeusaste", "Peli??net", "V?rin?tehosteet",
"Pelin nimi" },
{ "Nouveau jeu", "Paramètres", "Scores", "Instructions",
"A propos","Continuer", "Retour", "Suite", "Sortir",
"Niveau", "Sons", "Vibrations", "Jeu nom" },
{ "Neues Spiel", "Einstellungen", "Rekord", "Anleitung",
"über","Weiter", "Zurück", "Weiter", "Beenden",
"Ebene", "Ton", "Vibrationen", "Spiel name" }
};
/**
* Gets a string for the given key.
* @param key Integer key for string
* @return The string
*/
public static String getString(int key) {
String locale = System.getProperty("microedition.locale");
if (locale == null) {
locale = new String(""); // use empty instead of null
}
// find the index of the locale id
int localeIndex = -1;
for (int i = 0; i < supportedLocales.length; i++) {
if (locale.equals(supportedLocales[i])) {
localeIndex = i;
break;
}
}
// not found
if (localeIndex == -1) {
// defaults to first language, in this example English
return strings[0][key];
}
return strings[localeIndex][key];
}
}