今天周日，不适合出门，太冷了，俗说：一九二九不出手，三九四九零来走。。

我们的应用也可以有一些冬天的效果, 教大家做一个下雪的动画效果, 参考.

主要

(1) 隐藏status bar, 全屏显示图片.

(2) 绘制多个点, 实现移动效果.

(3) 回收点, 避免重复创建.

我喜欢用注释说话, 请大家多关注代码中的注释.

Github下载地址

1. 雪花类

雪花的属性包含: 随机量, 位置, 增量, 大小, 角度, 画笔.

绘画的过程中, 使用角度会移动点的位置, 每次速率都不同.

当雪花移出屏幕时, 会重新使用, 在屏幕的顶端重新落下.

算法参考.

/** * 雪花的类, 移动, 移出屏幕会重新设置位置. * <p/> * Created by wangchenlong on 16/1/24. */ public class SnowFlake { // 雪花的角度 private static final float ANGE_RANGE = 0.1f; // 角度范围 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PI private static final float ANGLE_SEED = 25f; // 角度随机种子 private static final float ANGLE_DIVISOR = 10000f; // 角度的分母 // 雪花的移动速度 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; // 随机控制器 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; // 画笔 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); } // 绘制雪花 public void draw(Canvas canvas) { int width = canvas.getWidth(); int height = canvas.getHeight(); move(width, height); canvas.drawCircle(mPosition.x, mPosition.y, mFlakeSize, mPaint); } // 移动雪花 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; // 随机晃动 mPosition.set((int) x, (int) y); // 移除屏幕, 重新开始 if (!isInside(width, height)) { reset(width); } } // 判断是否在其中 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; } } 随机数生成器, 包含区间随机和上界随机. /** * 随机生成器 * <p/> * Created by wangchenlong on 16/1/24. */ public class RandomGenerator { private static final Random RANDOM = new Random(); // 区间随机 public float getRandom(float lower, float upper) { float min = Math.min(lower, upper); float max = Math.max(lower, upper); return getRandom(max - min) + min; } // 上界随机 public float getRandom(float upper) { return RANDOM.nextFloat() * upper; } // 上界随机 public int getRandom(int upper) { return RANDOM.nextInt(upper); } }

2. 雪花视图

雪花视图, DELAY时间重绘, 绘制NUM_SNOWFLAKES个雪花.

初始化在onSizeChanged中进行, 绘制在onDraw中进行.

/** * 雪花视图, DELAY时间重绘, 绘制NUM_SNOWFLAKES个雪花 * <p/> * Created by wangchenlong on 16/1/24. */ public class SnowView extends View { private static final int NUM_SNOWFLAKES = 150; // 雪花数量 private static final int DELAY = 5; // 延迟 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); // 抗锯齿 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); } // 隔一段时间重绘一次, 动画效果 getHandler().postDelayed(runnable, DELAY); } // 重绘线程 private Runnable runnable = new Runnable() { @Override public void run() { invalidate(); } }; }

使用getHandler().postDelayed(runnable, DELAY);刷新页面.

3. 全屏布局

全屏布局

<"1.0" encoding="utf-8"?> <android.support.design.widget.CollapsingToolbarLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <FrameLayout android:layout_width="match_parent" android:layout_height="match_parent"> <ImageView android: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.SnowView android:layout_width="match_parent" android:layout_height="match_parent"/> </FrameLayout> </android.support.design.widget.CollapsingToolbarLayout>

status bar默认是不会被透明化的, 需要使用CollapsingToolbarLayout,

替换status bar的样式, 否则会留有一定高度, 即使透明也不会填充.

样式

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