实例分析JETBOY

实现原理：

启动以个单独的游戏线程，通过主VIEW中的ONCLIK事件中根据不同的线程状态，显示不同的VIEW和按钮状态。

private JetBoyThread mJetBoyThread; //游戏线程

private JetBoyView mJetBoyView; //游戏运行的VIEW

private Button mButton; //PLAY按钮

private Button mButtonRetry; //RETRy按钮

private TextView mTextView; //游戏中显示的帮助文本

private TextView mTimerView;//游戏时钟

程序入口点:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.jetboy" android:versionCode="1"
android:versionName="1.0.0">
<application android:icon="@drawable/icon"
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar">
<activity android:name=".JetBoy"
android:label="@string/app_name"
android:screenOrientation="landscape">
<intent-filter>
<action android:name="android.intent.action.MAIN " />
<category
android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-sdk android:minSdkVersion="3"></uses-sdk>
</manifest>

很明显是JETBOY.JAVA。

main.xml 中使用的是FrameLayout,在其中部署了上诉的VIEW和button。

onCreate中代码很简单，主要是取得VIEW和BUTTON,然后初始化mJetBoyThread和mJetBoyView；

public class JetBoy extends Activity implements View.OnClickListener

请注意这个实现的目的是为了在一个ONCLICK中处理所有按钮事件。主要逻辑都是在onClick(View v)实现。具体看看：

public void onClick(View v) {

if (mJetBoyThread.getGameState() == JetBoyThread.STATE_START) {
mButton.setText("PLAY!");
mTextView.setVisibility(View.VISIBLE);

mTextView.setText(R.string.helpText);
mJetBoyThread.setGameState(JetBoyThread.STATE_PLAY);

}
// we have entered game play, now we about to start running
else if (mJetBoyThread.getGameState() == JetBoyThread.STATE_PLAY) {
mButton.setVisibility(View.INVISIBLE);
mTextView.setVisibility(View.INVISIBLE);
mTimerView.setVisibility(View.VISIBLE);
mJetBoyThread.setGameState(JetBoyThread.STATE_RUNNING);

}
// this is a retry button
else if (mButtonRetry.equals(v)) {

mTextView.setText(R.string.helpText);

mButton.setText("PLAY!");
mButtonRetry.setVisibility(View.INVISIBLE);
// mButtonRestart.setVisibility(View.INVISIBLE);

mTextView.setVisibility(View.VISIBLE);
mButton.setText("PLAY!");
mButton.setVisibility(View.VISIBLE);

mJetBoyThread.setGameState(JetBoyThread.STATE_PLAY);

} else {
Log.d("JB VIEW", "unknown click " + v.getId());

Log.d("JB VIEW", "state is " + mJetBoyThread.mState);

}
}

很容易读懂。

另外实现两个onKeyDown和onKeyUp事件，处理游戏中按键的事件。

核心实现：JetBoyView

1 SurfaceView分析

public class JetBoyView extends SurfaceView implements SurfaceHolder.Callback{}

SurfaceView 在复杂的游戏开发中经常用到，提供一个可直接控制的画图界面，在Canvas可以绘制各种背景、人物、场景。

通过GetHolder()返回SurfaceHolde来实现对SurfaceView 的控制；

SurfaceHolder holder = getHolder();
holder.addCallback(this);//Add a Callback interface for this holder.

以上是该程序中的代码；

SurfaceHolder.Callback 通过这个接口可以获得Surface改变的信息；

public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {} //在surface的大小发生改变时激发

public void surfaceCreated(SurfaceHolder arg0) { }

//在创建时激发，一般在这里调用画图的线程

public void surfaceDestroyed(SurfaceHolder arg0) { }

//销毁时激发，一般在这里将画图的线程停止、释放

以上是实现的接口方法；

2 GameEvent

程序定义了两个GameEvent 子类KeyGameEvent和JetGameEvent，很容理解。

KeyGameEvent 来自键盘输入

JetGameEvent 来自 JetPlayer.

这里涉及到JetPlayer是什么？开发过游戏的应该很熟悉，我查了帮助，才搞清楚是做什么的。这里会涉及到一系列Jet的概念，从相关资料中得知：

JET 一个在嵌入式设备上的音乐播放器，包括那些运行机器人平台小的嵌入式设备。它允许应用程序在响应中的 MIDI 格式中包含交互式音乐音轨实时游戏事件和用户交互。

JET ENGINE 一个控制游戏声音特效的引擎，其使用MIDI格式，并可以控制游戏的时间进度（一个精确的时钟是一个游戏必不可少)

JetPlayer 提供了对JET content的访问

JetCreator 是一盒可以创建JET content的工具；

稍后会详细说明；

3 关键线程JetBoyThread

整个游戏的主线程，首先看看定义

class JetBoyThread extends Thread implements OnJetEventListener

它实现了OnJetEventListener接口，用来获取JetPlayer的事件；

先看看该线程主要完成什么功能：

• 处理JetPlayer和KEY事件；
• 2 绘制各种动画SurfaceView中的显示；
• 3 游戏状态的设置；
• 4 用户游戏数据的保存；

程序的逻辑

在仔细分析代码前，有必要看看程序的逻辑是如何实现的？线程是如何启动和运行的？

首先jetBoy:onCreate

JetBoyView:JetBoyView(Context context, AttributeSet attrs{

thread = new JetBoyThread(holder, context, new Handler();\\创建线程并在线程构造函数中初始化游戏状态；mState=STATE_START;setRunning(TRUE);

}

surfaceCreated 中启动线程thread.start();

开始执行JetBoyThread:run()//进入游戏状态集；这是执行的主体；会根据不同的游戏状态执行相应的操作。直到setRunning(false);

这时候等待用户操作；

jetBoy的onKeyDown，onKeyUp会触发JetBoyThread的doKeyDown和doKeyUp，将事件放到队列中，然后在updateGameState，检查mEventQueue，进行事件处理：

@Override
public boolean onKeyDown(int keyCode, KeyEvent msg) {

if (keyCode == 4)
super.onKeyDown(keyCode, msg);

return mJetBoyThread.doKeyDown(keyCode, msg);
}

public boolean doKeyDown(int keyCode, KeyEvent msg) {
mEventQueue.add(new KeyGameEvent(keyCode, false, msg));

return true;
}

protected void updateGameState() {
// Process any game events and apply them
while (true) {
GameEvent event = mEventQueue.poll();
if (event == null)
break;

// Log.d(TAG,"*** EVENT = " + event);

// Process keys tracking the input context to pass in to later
// calls
if (event instanceof KeyGameEvent) {
// Process the key for affects other then asteroid hits
mKeyContext = processKeyEvent((KeyGameEvent)event, mKeyContext);

// Update laser state. Having this here allows the laser to
// be triggered right when the key is
// pressed. If we comment this out the laser will only be
// turned on when updateLaser is called
// when processing a timer event below.
updateLaser(mKeyContext);

}
// JET events trigger a state update
else if (event instanceof JetGameEvent) {
JetGameEvent jetEvent = (JetGameEvent)event;

// Only update state on a timer event
if (jetEvent.value == TIMER_EVENT) {
// Note the time of the last beat
mLastBeatTime = System.currentTimeMillis();

// Update laser state, turning it on if a key has been
// pressed or off if it has been
// on for too long.
updateLaser(mKeyContext);

// Update explosions before we update asteroids because
// updateAsteroids may add
// new explosions that we do not want updated until next
// frame
updateExplosions(mKeyContext);

// Update asteroid positions, hit status and animations
updateAsteroids(mKeyContext);
}

processJetEvent(jetEvent.player, jetEvent.segment, jetEvent.track, jetEvent.channel, jetEvent.controller, jetEvent.value);
}
}
}

逻辑应该很清楚了吧。