自定义View——天气下雨效果

项目要实现下雨效果，在StylingAndroid中发现一篇有关下雪的效果，稍作修改，便可以实现下雨效果:
原地址：https://blog.stylingandroid.com/snowfall/

public class RainView extends View {
    private static final int NUM_RAIN_FLAKES = 100;
    private static final int DELAY = 5;

    private RainFlake[] rainflakes;

    public RainView(Context context) {
        super(context);
    }

    public RainView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public RainView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    protected void resize(int width, int height) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.WHITE);
        paint.setStyle(Paint.Style.FILL);
        rainflakes = new RainFlake[NUM_RAIN_FLAKES];
        for (int i = 0; i < NUM_RAIN_FLAKES; i++) {
            rainflakes[i] = RainFlake.create(width, height, paint);
        }
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        if (w != oldw || h != oldh) {
            resize(w, h);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        for (RainFlake rainFlake : rainflakes) {
            rainFlake.draw(canvas);
        }
        getHandler().postDelayed(runnable, DELAY);
    }

    private Runnable runnable = new Runnable() {
        @Override
        public void run() {
            invalidate();
        }
    };
}

class RainFlake {
    private static final float ANGE_RANGE = 0.1f;
    private static final float HALF_ANGLE_RANGE = ANGE_RANGE / 2f;
    private static final float HALF_PI = (float) Math.PI / 2f;
    private static final float ANGLE_SEED = 25f;
    private static final float ANGLE_DIVISOR = 10000f;
    private static final float INCREMENT_LOWER = 4f;
    private static final float INCREMENT_UPPER = 6f;
    private static final float FLAKE_SIZE_LOWER = 7f;
    private static final float FLAKE_SIZE_UPPER = 25f;

    private final Random random;
    private final Point position;
    private float angle;
    private final float increment;
    private final float flakeSize;
    private final Paint paint;

    public static RainFlake create(int width, int height, Paint paint) {
        Random random = new Random();
        int x = random.getRandom(width);
        int y = random.getRandom(height);
        Point position = new Point(x, y);
        float angle = random.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;
        float increment = random.getRandom(INCREMENT_LOWER, INCREMENT_UPPER);
        float flakeSize = random.getRandom(FLAKE_SIZE_LOWER, FLAKE_SIZE_UPPER);
        return new RainFlake(random, position, angle, increment, flakeSize, paint);
    }

    RainFlake(Random random, Point position, float angle, float increment, float flakeSize,
              Paint paint) {
        this.random = random;
        this.position = position;
        this.angle = angle;
        this.increment = increment;
        this.flakeSize = flakeSize;
        this.paint = paint;
    }

    private void move(int width, int height) {
    //    double x = position.x + (increment * Math.cos(angle));
        double x = position.x;
        double y = position.y + (increment * Math.sin(angle));

        angle += random.getRandom(-ANGLE_SEED, ANGLE_SEED) / ANGLE_DIVISOR;

        position.set((int) x, (int) y);

        if (!isInside(width, height)) {
            reset(width);
        }
    }

    private boolean isInside(int width, int height) {
        int x = position.x;
        int y = position.y;
        return x >= -flakeSize - 1 && x + flakeSize <= width && y >= -flakeSize - 1 && y - flakeSize < height;
    }

    private void reset(int width) {
        position.x = random.getRandom(width);
        position.y = (int) (-flakeSize - 1);
        angle = random.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;
    }

    public void draw(Canvas canvas) {
        int width = canvas.getWidth();
        int height = canvas.getHeight();
        move(width, height);
        canvas.drawLine(position.x, position.y, position.x,position.y+flakeSize, paint);
    }
}

class Random {
    private static final java.util.Random RANDOM = new java.util.Random();

    public float getRandom(float lower, float upper) {
        float min = Math.min(lower, upper);
        float max = Math.max(lower, upper);
        return getRandom(max - min) + min;
    }

    public float getRandom(float upper) {
        return RANDOM.nextFloat() * upper;
    }

    public int getRandom(int upper) {
        return RANDOM.nextInt(upper);
    }

}