我需要“开始android游戏”代码的解释

这几天我在读《Beginning Android Games》这本书。但我坚持理解代码。

您可以在此处检查或下载代码：http://code.google.com/p/beginnginandroidgames2/downloads/list http://code.google.com/p/beginnginandroidgames2/downloads/list

我指的项目是ch06-mr-mom。该活动称为MrNomGame:

public abstract class AndroidGame extends Activity implements Game {

    AndroidFastRenderView renderView;
    Graphics graphics;
    Audio audio;
    Input input;
    FileIO fileIO;
    Screen screen;
    WakeLock wakeLock;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);

        boolean isLandscape = getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE;
        int frameBufferWidth = isLandscape ? 480 : 320;
        int frameBufferHeight = isLandscape ? 320 : 480;
        Bitmap frameBuffer = Bitmap.createBitmap(frameBufferWidth,
                frameBufferHeight, Config.RGB_565);

        float scaleX = (float) frameBufferWidth
                / getWindowManager().getDefaultDisplay().getWidth();
        float scaleY = (float) frameBufferHeight
                / getWindowManager().getDefaultDisplay().getHeight();

        renderView = new AndroidFastRenderView(this, frameBuffer);
        graphics = new AndroidGraphics(getAssets(), frameBuffer);
        fileIO = new AndroidFileIO(this);
        audio = new AndroidAudio(this);
        input = new AndroidInput(this, renderView, scaleX, scaleY);
        screen = getStartScreen();
        setContentView(renderView);

        PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
        wakeLock = powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK, "GLGame");
    }

    @Override
    public void onResume() {
        super.onResume();
        wakeLock.acquire();
        screen.resume();
        renderView.resume();
    }

    @Override
    public void onPause() {
        super.onPause();
        wakeLock.release();
        renderView.pause();
        screen.pause();

        if (isFinishing())
            screen.dispose();
    }

    public Input getInput() {
        return input;
    }

    public FileIO getFileIO() {
        return fileIO;
    }

    public Graphics getGraphics() {
        return graphics;
    }

    public Audio getAudio() {
        return audio;
    }

    public void setScreen(Screen screen) {
        if (screen == null)
            throw new IllegalArgumentException("Screen must not be null");

        this.screen.pause();
        this.screen.dispose();
        screen.resume();
        screen.update(0);
        this.screen = screen;
    }

    public Screen getCurrentScreen() {
        return screen;
    }
}

类实现接口Game :

package com.badlogic.androidgames.framework;

public interface Game {
    public Input getInput();
    public FileIO getFileIO();
    public Graphics getGraphics();
    public Audio getAudio();
    public void setScreen(Screen screen);
    public Screen getCurrentScreen();
    public Screen getStartScreen();
}

我的第一个问题是：我错过了该方法的实现getStartScreen()接口的Game。通常我必须实现接口的所有方法。

无论如何，现在onCreate在跑。在这一行：

screen = getStartScreen();

程序回到原来的类MrNomGame，其中方法getStartScreen()给出一个对象LoadingScreen到变量screen. Class LoadingScreen:

public class LoadingScreen extends Screen {

    public LoadingScreen(Game game) {
        super(game);
    }

    public void update(float deltaTime) {
        Graphics g = game.getGraphics();
        Assets.background = g.newPixmap("background.png", PixmapFormat.RGB565);
        Assets.logo = g.newPixmap("logo.png", PixmapFormat.ARGB4444);
        Assets.mainMenu = g.newPixmap("mainmenu.png", PixmapFormat.ARGB4444);
        Assets.buttons = g.newPixmap("buttons.png", PixmapFormat.ARGB4444);
        Assets.help1 = g.newPixmap("help1.png", PixmapFormat.ARGB4444);
        Assets.help2 = g.newPixmap("help2.png", PixmapFormat.ARGB4444);
        Assets.help3 = g.newPixmap("help3.png", PixmapFormat.ARGB4444);
        Assets.numbers = g.newPixmap("numbers.png", PixmapFormat.ARGB4444);
        Assets.ready = g.newPixmap("ready.png", PixmapFormat.ARGB4444);
        Assets.pause = g.newPixmap("pausemenu.png", PixmapFormat.ARGB4444);
        Assets.gameOver = g.newPixmap("gameover.png", PixmapFormat.ARGB4444);
        Assets.headUp = g.newPixmap("headup.png", PixmapFormat.ARGB4444);
        Assets.headLeft = g.newPixmap("headleft.png", PixmapFormat.ARGB4444);
        Assets.headDown = g.newPixmap("headdown.png", PixmapFormat.ARGB4444);
        Assets.headRight = g.newPixmap("headright.png", PixmapFormat.ARGB4444);
        Assets.tail = g.newPixmap("tail.png", PixmapFormat.ARGB4444);
        Assets.stain1 = g.newPixmap("stain1.png", PixmapFormat.ARGB4444);
        Assets.stain2 = g.newPixmap("stain2.png", PixmapFormat.ARGB4444);
        Assets.stain3 = g.newPixmap("stain3.png", PixmapFormat.ARGB4444);
        Assets.click = game.getAudio().newSound("click.ogg");
        Assets.eat = game.getAudio().newSound("eat.ogg");
        Assets.bitten = game.getAudio().newSound("bitten.ogg");
        Settings.load(game.getFileIO());
        game.setScreen(new MainMenuScreen(game));
    }

    public void present(float deltaTime) {

    }

    public void pause() {

    }

    public void resume() {

    }

    public void dispose() {

    }
}

Class Screen:

public abstract class Screen {
    protected final Game game;

    public Screen(Game game) {
        this.game = game;
    }

    public abstract void update(float deltaTime);
    public abstract void present(float deltaTime);
    public abstract void pause();
    public abstract void resume();
    public abstract void dispose();
}

经过一定时间后，onCreate()方法完毕。但是在调试模式下我的手机屏幕已经黑了。看来程序是在循环中。我可以随意按 F6。但是当我恢复时，将显示主菜单。如果你查看代码，你会发现主菜单将调用update()的方法loadingScreen.

我的大问题是：之后会发生什么onCreate()方法完毕以及程序如何进入update()的方法loadingScreen?

我知道这是很多代码。但理解它对我来说非常有用。

对于你的第一个问题：AndroidGame is an abstract班级。这意味着它不必实现所有方法Game，只要其中一个类扩展AndroidGame做这个。从代码中可以看出，这是在MrNomGame:

public class MrNomGame extends AndroidGame {
    public Screen getStartScreen() {
        return new LoadingScreen(this); 
    }
} 

现在回答你的大问题：

In onCreate，创建渲染器：

renderView = new AndroidFastRenderView(this, frameBuffer);

如果你看一下那个类，你就会发现onResume创建一个运行以下代码的新线程：

public void run() {
    Rect dstRect = new Rect();
    long startTime = System.nanoTime();
    while(running) {  
        if(!holder.getSurface().isValid())
            continue;           

        float deltaTime = (System.nanoTime()-startTime) / 1000000000.0f;
        startTime = System.nanoTime();

        game.getCurrentScreen().update(deltaTime);
        game.getCurrentScreen().present(deltaTime);

        Canvas canvas = holder.lockCanvas();
        canvas.getClipBounds(dstRect);
        canvas.drawBitmap(framebuffer, null, dstRect, null);
        holder.unlockCanvasAndPost(canvas);
    }
}

所以，它会重复调用update在当前屏幕上，这是LoadingScreen.