自定义View——天气下雨效果

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);
}

}