使用SurfaceView实现京东首页圣诞雪花飘落效果

直接上图，GIF制作太麻烦了。

就是上面的雪花会慢慢飘落，但是不影响下面的点击事件，效果全凭想象。

2551545573969_.pic.jpg

首先说明一下，下面就是一张截的京东首页图，然后上面的雪花是使用SurfaceView来制作的，为了模拟点击事件，在SurfaceView下面放了一个按钮用来测试事件分发。

SurfaceView

在Android系统中，有一种特殊的视图，称为SurfaceView，它拥有独立的绘图表面，即它不与其宿主窗口共享同一个绘图表面。由于拥有独立的绘图表面，因此SurfaceView的UI就可以在一个独立的线程中进行绘制。又由于不会占用主线程资源，SurfaceView一方面可以实现复杂而高效的UI，另一方面又不会导致用户输入得不到及时响应。
摘自https://blog.csdn.net/luoshengyang/article/details/8661317/，老罗的博客详细介绍了SurfaceView实现原理。

总结下来就是使用SurfaceView可以在一个单独的线程去更新UI，那么既然在单独的线程更新UI，那就肯定不会影响主线程了，所以说SurfaceView非常适合这种雪花效果了。

创建Activity的布局

MySurfaceView.java

  public static final String TAG = "MySurfaceView";
  private SurfaceHolder mHolder;
  private Thread mThread;
  private Canvas mCanvas;
  private boolean bIsRunning = false;
  private List mSnowList = new ArrayList<>();
  private static final int snowCount = 16;
  private Paint mPaint;
  private Bitmap mBitmap;


  public MySurfaceView(Context context) {
    this(context, null);
  }

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

  private void init() {
    Log.d(TAG, "init");
    setZOrderOnTop(true);
    getHolder().setFormat(PixelFormat.TRANSLUCENT);
    // 从父类SurfaceView中获取到SurfaceHolder，然后通过SurfaceHolder来添加监听，
    // 监听SurfaceView的生命周期，也就是下面的三个方法
    mHolder = getHolder();
    mHolder.addCallback(this);

    // 设置获得焦点
    setFocusable(true);
    setFocusableInTouchMode(true);
    // 设置常亮
    setKeepScreenOn(true);
    //初始化雪花
    for(int i=0;i1920){
              snow.startTime = System.currentTimeMillis();
            }
            Bitmap bitmap = rotateBitmap(mBitmap,10*i);
            mCanvas.drawBitmap(bitmap,x,y,mPaint);
          }
        }
      } catch (Exception e) {
        Log.d(TAG,"e is "+e.getMessage());

      } finally {
        if (mCanvas != null) {
          Log.d(TAG,"unlockCanvasAndPost");
          mHolder.unlockCanvasAndPost(mCanvas);
        }
      }

    }
  }

  @Override
  public void surfaceDestroyed(SurfaceHolder holder) {
    Log.d(TAG, "surfaceDestroyed");
    bIsRunning = false;
  }

  @Override
  public boolean dispatchTouchEvent(MotionEvent event) {
    return false;
  }

  private Bitmap rotateBitmap(Bitmap origin, float dgress) {
    Bitmap newBM=null;
    try {
      if (origin == null) {
        return null;
      }
      int width = origin.getWidth();
      int height = origin.getHeight();
      Matrix matrix = new Matrix();
      matrix.setRotate(dgress);
      // 围绕原地进行旋转
      newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
      if (newBM.equals(origin)) {
        return newBM;
      }
    }
    catch (Exception e){
      Log.d(TAG,"e is "+e.getMessage());
    }

    return newBM;
  }


  private Bitmap decodeSampledBitmapFromResource(Resources resources,
                                                 int resId, int reqWidth, int reqHeight) {
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(resources, resId, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(resources, resId, options);
  }

  private int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
    final int height = options.outHeight;
    Log.i(TAG,""+height);
    final int width = options.outWidth;
    Log.i(TAG,""+width);
    int inSampleSize = 1;

    if (height > reqHeight || width > reqWidth) {

      final int halfHeight = height / 2;
      final int halfWidth = width / 2;

      // Calculate the largest inSampleSize value that is a power of 2 and keeps both
      // height and width larger than the requested height and width.
      while ((halfHeight / inSampleSize) > reqHeight
              && (halfWidth / inSampleSize) > reqWidth) {
        inSampleSize *= 2;
      }
    }

    return inSampleSize;
  }

代码很简单哈，就不解释了。直接show my code for u。