圣诞雪花纷飞自定义View

github地址：https://github.com/shuaijia/JSBaseDemo/blob/master/app/src/main/java/com/jia/demo/view/SnowView.java

先定义下实体类吧：

/** * Description: 雪花效果实体类 * Created by jia on 2017/12/25. * 人之所以能，是相信能 */public class Snow {    private float x;    private float y;    private int alfa;    private float size;    private float speed;    private int srcType;    public Snow(float x, float y, int alfa, float size, float speed, int srcType) {        this.x = x;        this.y = y;        this.alfa = alfa;        this.size = size;        this.speed = speed;        this.srcType = srcType;    }    ...// get、set方法省略}

实现思路：

说起这种雪花纷飞的效果，大家都会立刻想到用属性动画，通过各种动画组合、插值器的使用（当然使用贝塞尔曲线会更炫），就可以很轻松的实现如上效果，但我们今天换种思路来实现：

因为所有的雪花需要实时在移动位置，所以想开启子线程去控制所以雪花位置，但因为在子线程中刷新view，就采用SurfaceView来实现。

SurfaceView继承之View，但拥有独立的绘制表面，即它不与其宿主窗口共享同一个绘图表面，可以单独在一个线程进行绘制，并不会占用主线程的资源。

自定义view

    public SnowView(Context context, AttributeSet attrs) {        super(context, attrs);        surfaceHolder = this.getHolder();        surfaceHolder.addCallback(this);        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);        bgBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.snow_bg);        init();    }    private void init() {        DisplayMetrics dm = getResources().getDisplayMetrics();        snows = new ArrayList<>();        float x, y, size, speed;        int alfa, srcType;        for (int i = 0; i < maxCount; i++) {            x = (float) Math.floor(Math.random() * dm.widthPixels);//初始X坐标            y = (float) Math.floor(Math.random() * dm.heightPixels);//初始Y坐标            size = (float) ((Math.random() * 15f) + 20f);//初始半径            speed = (float) ((Math.random() * 6) + 5);            alfa = (int) Math.floor(100 * Math.random() + 155);            srcType = (int) (Math.random() + 0.5);            snows.add(new Snow(x, y, alfa, size, speed, srcType));        }    }

初始化SnowView，我们定义一屏雪花数（如100），循环100次，使用随机数设置雪花位置、大小、透明度等属性，并放入集合中。

    /**     * 绘制进程     */    class DrawThread extends Thread {        public boolean isRunning = false;        private Canvas canvas;        public DrawThread() {            isRunning = true;        }        @Override        public void run() {            super.run();            while (isRunning) {                synchronized (surfaceHolder) {                    // Start editing the pixels in the surface.  The returned Canvas can be used to draw into the surface's bitmap.                    canvas = surfaceHolder.lockCanvas();                    drawSprite(canvas);                    for (int i = 0; i < maxCount; i++) {                        curSnow = snows.get(i);                        float size = curSnow.getSize();                        float speed = curSnow.getSpeed();                        int alfa = curSnow.getAlfa();                        float x = curSnow.getX();                        float y = curSnow.getY() + speed;                        int type = curSnow.getSrcType();                        if (y >= canvas.getHeight() || x >= canvas.getWidth()) {                            y = 0;                            x = (float) Math.floor(Math.random() * canvas.getWidth());//初始X坐标                        }                        mPaint.setAlpha(alfa);                        Bitmap snowBitmap;                        if (type == 1) {                            snowBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.snow1);                        } else {                            snowBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.snow2);                        }                        RectF rect = new RectF(x, y, x + size, y + size);                        canvas.drawBitmap(snowBitmap, null, rect, mPaint);                        snows.set(i, new Snow(x, y, alfa, size, speed, type));                    }                    surfaceHolder.unlockCanvasAndPost(canvas);                }            }        }        public void stopThread() {            isRunning = false;            boolean workIsNotFinish = true;            while (workIsNotFinish) {                try {                    this.join();// 保证run方法执行完毕                } catch (InterruptedException e) {                    e.printStackTrace();                }                workIsNotFinish = false;            }        }    }    private void drawSprite(Canvas canvas) {        //清屏操作        canvas.drawBitmap(bgBitmap, null, new Rect(0, 0, canvas.getWidth(), canvas.getHeight()), null);    }

在run方法中获取到当前绘制的canvas，然后循环进行绘制，绘制完成后surfaceHolder.unlockCanvasAndPost(canvas)，将画布显示在屏幕上。

注意整个循环执行次数多，但我们必须保证全部绘制完再切换线程，所以我们使用synchronized关键字。

    @Override    public void surfaceCreated(SurfaceHolder holder) {        if (null == mDrawThread) {            mDrawThread = new DrawThread();            mDrawThread.start();        }    }    @Override    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {    }    @Override    public void surfaceDestroyed(SurfaceHolder holder) {        if (null != mDrawThread) {            mDrawThread.stopThread();        }    }

在surface创建的回调中开启线程，在destroy方法中关闭线程，就ok了！

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