0

我想用 SurfaceView 创建演示应用程序。但是在一行“ GameThread = gameView.getThread(); ”中收到错误 NullPointerException这是我的整个代码片段

主要活动：

 public class MainActivity extends Activity {

GameView gameView;
TutorialThread GameThread;
Button btnStart, btnStop;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d("OnCreate -", "I am in onCreate method..");
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

    requestWindowFeature(Window.FEATURE_NO_TITLE);

    // get handles to the GameView from XML and the Tutorial thread.
    gameView = (GameView) findViewById(R.id.gameView);

    //Log.d("OnCreate -", ""+gameView.TAG);

    GameThread = gameView.getThread();

    //GameThread.start();
    ClickListener clickListener = new ClickListener();

    // look up the happy shiny button
    btnStart = (Button) findViewById(R.id.btnStart);
    btnStart.setOnClickListener(clickListener);

    btnStop = (Button) findViewById(R.id.btnStop);
    btnStop.setOnClickListener(clickListener);

    setContentView(R.layout.activity_main);
}

  class ClickListener implements View.OnClickListener {

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

        switch (v.getId()) {

        case R.id.btnStart:
            /*
             * if (GameThread.mState == GameThread.STATE_PLAY) {
             * GameThread.setGameState(TutorialThread.STATE_RUNNING);
             * 
             * }
             */
            makeToast("This is Start Button");
            break;

        case R.id.btnStop:
            /*
             * if (GameThread.mState == GameThread.STATE_RUNNING) { //
             * GameThread.setGameState(TutorialThread.STATE_PLAY); }
             */
            makeToast("This is Stop Button");
            break;

        }

    }

    private void makeToast(String string) {
        // TODO Auto-generated method stub
        Toast.makeText(MainActivity.this, string,      Toast.LENGTH_LONG).show();
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

}

和 GameView 类是： -

   public class GameView extends SurfaceView implements SurfaceHolder.Callback {

String TAG = "GameView";
private TutorialThread _thread;

public GameView(Context context, AttributeSet attrs) {
    super(context, attrs);
    // TODO Auto-generated constructor stub
    getHolder().addCallback(this);
    _thread = new TutorialThread(getHolder(), context);
    setFocusable(true);
}

public TutorialThread getThread() {
    return _thread;
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
        int height) {
    // TODO Auto-generated method stub

}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    // TODO Auto-generated method stub
    _thread.setRunning(true);
    _thread.start();
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    // TODO Auto-generated method stub

    // we have to tell thread to shut down & wait for it to finish, or else
    // it might touch the Surface after we return and explode
    boolean retry = true;
    _thread.setRunning(false);
    while (retry) {
        try {
            _thread.join();
            retry = false;
        } catch (InterruptedException e) {
            // we will try it again and again...
        }
    }
   }

  }

  class TutorialThread extends Thread {
String TAG = "TutorialThread";
private SurfaceHolder _surfaceHolder;
private boolean _run = false;
Bitmap bitmapDroid;

/**
 * State-tracking constants.
 */

public static final int STATE_PLAY = 0;
public static final int STATE_RUNNING = 1;
public int mState = STATE_PLAY;

Resources mRes;

/** Handle to the application context, used to e.g. fetch Drawables. */
private Context mContext;

float droidx = 200, droidy = 200;

public TutorialThread(SurfaceHolder surfaceHolder, Context context) {
    _surfaceHolder = surfaceHolder;
    mContext = context;
    mRes = context.getResources();
    // create droid and load bitmap
    bitmapDroid = BitmapFactory
            .decodeResource(mRes, R.drawable.ic_launcher);

}

public void setRunning(boolean run) {
    _run = run;
}

@Override
public void run() {
    Canvas c;
    while (_run) {
        c = null;
        try {
            c = _surfaceHolder.lockCanvas(null);
            synchronized (_surfaceHolder) {
                onDraw(c);
            }
        } finally {
            // do this in a finally so that if an exception is thrown
            // during the above, we don't leave the Surface in an
            // inconsistent state
            if (c != null) {
                _surfaceHolder.unlockCanvasAndPost(c);
            }
        }
    }
}

public void onDraw(Canvas canvas) {

    canvas.drawColor(Color.rgb(187, 255, 255));
    canvas.drawBitmap(bitmapDroid, droidx - (bitmapDroid.getWidth() / 2),
            droidy - (bitmapDroid.getHeight() / 2), null);

}

  }

布局声明为：

  <com.example.surfaceviewdemo.GameView
    android:id="@+id/gameView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="1" />
4

1 回答 1

2

您需要首先设置您的内容视图，然后才能从布局中获取您的视图。所以，

setContentView(R.layout.activity_main);

应该出现在您的上方

gameView = (GameView) findViewById(R.id.gameView);

于 2013-03-14T05:49:23.880 回答