java将TextView放在视图中

Question

我正在尝试这个降雪计划http://code.google.com/p/安卓-30days-apps/source/browse/trunk/08day/src/com/bakhtiyor/安卓/snowfall/SnowFall.java?r=27

我需要把TextView放在View类中（类SnowFallView扩展了View，第42行），我该怎么做呢

我可以实例化TextView并像这样添加它吗

 package in.isuru.animate;



 public class SnowFall extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            SnowFallView snowFallView = new SnowFallView(this);
            setContentView(snowFallView);
            snowFallView.setBackgroundDrawable(getResources().getDrawable(R.drawable.background_image));

    }

    private class SnowFallView extends View {
            private int snow_flake_count = 5;
            private final List<Drawable> drawables = new ArrayList<Drawable>();
            private int[][] coords;
            private final Drawable snow_flake;
            private TextView countDownView;

            public SnowFallView(Context context) {
                    super(context);
                    setFocusable(true);
                    setFocusableInTouchMode(true);

                    snow_flake = context.getResources().getDrawable(R.drawable.snow_flake);
                    snow_flake.setBounds(0, 0, snow_flake.getIntrinsicWidth(), snow_flake
                            .getIntrinsicHeight());

                    countDownView = new TextView(context);
                    countDownView.setText("It's working");
                    addContentView(countDownView, null);

                    //LayoutInflater inflater = getLayoutInflater();
                    //getWindow().addContentView(inflater.inflate(R.layout.text_layout, null), new ViewGroup.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT,
                    //ViewGroup.LayoutParams.FILL_PARENT));
            }

            @Override
            protected void onSizeChanged(int width, int height, int oldw, int oldh) {
                    super.onSizeChanged(width, height, oldw, oldh);
                    Random random = new Random();
                    Interpolator interpolator = new LinearInterpolator();

                    snow_flake_count = Math.max(width, height) / 20;
                    coords = new int[snow_flake_count][];
                    drawables.clear();
                    for (int i = 0; i < snow_flake_count; i++) {
                            Animation animation = new TranslateAnimation(0, height / 10
                                    - random.nextInt(height / 5), 0, height + 30);
                            animation.setDuration(10 * height + random.nextInt(5 * height));
                            animation.setRepeatCount(-1);
                            animation.initialize(10, 10, 10, 10);
                            animation.setInterpolator(interpolator);

                            coords[i] = new int[] { random.nextInt(width - 30), -30 };

                            drawables.add(new AnimateDrawable(snow_flake, animation));
                            animation.setStartOffset(random.nextInt(20 * height));
                            animation.startNow();
                    }
            }

            @Override
            protected void onDraw(Canvas canvas) {
                    for (int i = 0; i < snow_flake_count; i++) {
                            Drawable drawable = drawables.get(i);
                            canvas.save();
                            canvas.translate(coords[i][0], coords[i][1]);
                            drawable.draw(canvas);
                            canvas.restore();
                    }
                    invalidate();
            }

    } 
}

但当我这样做时，我会出错

06-04 00:22:22.364:E/AndroidRuntime（359）：java。lang.RuntimeException:无法启动活动组件信息{in.isuru.animate/in.isuru.animate.SnowFall}:java。lang.NullPointerException

附言：所有的进口都完成了