/*** 雪花的類, 移動, 移出屏幕會重新設置位置.* <p/>* Created by wangchenlong on 16/1/24.*/public class SnowFlake {// 雪花的角度private static final float ANGE_RANGE = 0.1f; // 角度范圍private static final float HALF_ANGLE_RANGE = ANGE_RANGE / 2f; // 一般的角度private static final float HALF_PI = (float) Math.PI / 2f; // 半PIprivate static final float ANGLE_SEED = 25f; // 角度隨機種子private static final float ANGLE_DIVISOR = 10000f; // 角度的分母// 雪花的移動速度private static final float INCREMENT_LOWER = 2f;private static final float INCREMENT_UPPER = 4f;// 雪花的大小private static final float FLAKE_SIZE_LOWER = 7f;private static final float FLAKE_SIZE_UPPER = 20f;private final RandomGenerator mRandom; // 隨機控制器private final Point mPosition; // 雪花位置private float mAngle; // 角度private final float mIncrement; // 雪花的速度private final float mFlakeSize; // 雪花的大小private final Paint mPaint; // 畫筆private SnowFlake(RandomGenerator random, Point position, float angle, float increment, float flakeSize, Paint paint) {mRandom = random;mPosition = position;mIncrement = increment;mFlakeSize = flakeSize;mPaint = paint;mAngle = angle;}public static SnowFlake create(int width, int height, Paint paint) {RandomGenerator random = new RandomGenerator();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 SnowFlake(random, position, angle, increment, flakeSize, paint);}// 繪制雪花public void draw(Canvas canvas) {int width = canvas.getWidth();int height = canvas.getHeight();move(width, height);canvas.drawCircle(mPosition.x, mPosition.y, mFlakeSize, mPaint);}// 移動雪花private void move(int width, int height) {double x = mPosition.x + (mIncrement * Math.cos(mAngle));double y = mPosition.y + (mIncrement * Math.sin(mAngle));mAngle += mRandom.getRandom(-ANGLE_SEED, ANGLE_SEED) / ANGLE_DIVISOR; // 隨機晃動mPosition.set((int) x, (int) y);// 移除屏幕, 重新開始if (!isInside(width, height)) {reset(width);}}// 判斷是否在其中private boolean isInside(int width, int height) {int x = mPosition.x;int y = mPosition.y;return x >= -mFlakeSize - 1 && x + mFlakeSize <= width && y >= -mFlakeSize - 1 && y - mFlakeSize < height;}// 重置雪花private void reset(int width) {mPosition.x = mRandom.getRandom(width);mPosition.y = (int) (-mFlakeSize - 1); // 最上面mAngle = mRandom.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;}}隨機數生成器, 包含區間隨機和上界隨機./*** 隨機生成器* <p/>* Created by wangchenlong on 16/1/24.*/public class RandomGenerator {private static final Random RANDOM = new Random();// 區間隨機public float getRandom(float lower, float upper) {float min = Math.min(lower, upper);float max = Math.max(lower, upper);return getRandom(max - min) + min;}// 上界隨機public float getRandom(float upper) {return RANDOM.nextFloat() * upper;}// 上界隨機public int getRandom(int upper) {return RANDOM.nextInt(upper);}}

/*** 雪花視圖, DELAY時間重繪, 繪制NUM_SNOWFLAKES個雪花* <p/>* Created by wangchenlong on 16/1/24.*/public class SnowView extends View {private static final int NUM_SNOWFLAKES = 150; // 雪花數量private static final int DELAY = 5; // 延遲private SnowFlake[] mSnowFlakes; // 雪花public SnowView(Context context) {super(context);}public SnowView(Context context, AttributeSet attrs) {super(context, attrs);}public SnowView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}@TargetApi(21)public SnowView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {super(context, attrs, defStyleAttr, defStyleRes);}@Override protected void onSizeChanged(int w, int h, int oldw, int oldh) {super.onSizeChanged(w, h, oldw, oldh);if (w != oldw || h != oldh) {initSnow(w, h);}}private void initSnow(int width, int height) {Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); // 抗鋸齒paint.setColor(Color.WHITE); // 白色雪花paint.setStyle(Paint.Style.FILL); // 填充;mSnowFlakes = new SnowFlake[NUM_SNOWFLAKES];for (int i = 0; i < NUM_SNOWFLAKES; ++i) {mSnowFlakes[i] = SnowFlake.create(width, height, paint);}}@Override protected void onDraw(Canvas canvas) {super.onDraw(canvas);for (SnowFlake s : mSnowFlakes) {s.draw(canvas);}// 隔一段時間重繪一次, 動畫效果getHandler().postDelayed(runnable, DELAY);}// 重繪線程private Runnable runnable = new Runnable() {@Overridepublic void run() {invalidate();}};}

<?xml version="1.0" encoding="utf-8"?><android.support.design.widget.CollapsingToolbarLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"><FrameLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"><ImageViewandroid:layout_width="match_parent"android:layout_height="match_parent"android:contentDescription="@null"android:scaleType="centerCrop"android:src="@drawable/christmas"/><me.chunyu.spike.wcl_snowfall_demo.views.SnowViewandroid:layout_width="match_parent"android:layout_height="match_parent"/></FrameLayout></android.support.design.widget.CollapsingToolbarLayout>

<?xml version="1.0" encoding="utf-8"?><resources><style name="AppTheme.NoStatusBar"><item name="android:windowTranslucentStatus">true</item></style></resources>