呼吸频率页面

呼吸频率页面需要对传入不同的分贝数进行刷新，将新采集的声音大小动态地展示出来，这个类可以使用前边的工具类World获取当前的分贝值，有过渡的缓慢刷新分贝仪页面。
代码：

public class SoundDiscView extends ImageView {
private float scaleWidth, scaleHeight;
private int newWidth, newHeight;
private Matrix mMatrix = new Matrix();
private Bitmap indicatorBitmap;
private Paint paint = new Paint();
static final long ANIMATION_INTERVAL = 20;

public SoundDiscView(Context context) {
    super(context);
}

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

private void init() {
    Bitmap myBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.noise_index);
    int bitmapWidth = myBitmap.getWidth();
    int bitmapHeight = myBitmap.getHeight();
    newWidth = getWidth();
    newHeight = getHeight();
    scaleWidth = ((float) newWidth) / (float) bitmapWidth;  // 获取缩放比例
    scaleHeight = ((float) newHeight) / (float) bitmapHeight;  //获取缩放比例
    mMatrix.postScale(scaleWidth, scaleHeight);   //设置mMatrix的缩放比例
    indicatorBitmap = Bitmap.createBitmap(myBitmap, 0, 0, bitmapWidth, bitmapHeight, mMatrix, true);  //获取同等和背景宽高的指针图的bitmap

    paint = new Paint();
    paint.setTextSize(18 * ScreenUtil.getDensity(getContext()));
    paint.setAntiAlias(true);  //抗锯齿
    paint.setTextAlign(Paint.Align.CENTER);
    paint.setColor(Color.WHITE);
}

public void refresh() {
    postInvalidateDelayed(ANIMATION_INTERVAL); //子线程刷新view
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (indicatorBitmap == null) {
        init();
    }
    mMatrix.setRotate(getAngle(World.dbCount), newWidth / 2, newHeight * 215 / 460);   //片相对位置
    canvas.drawBitmap(indicatorBitmap, mMatrix, paint);
    canvas.drawText((int) World.dbCount + " DB", newWidth / 2, newHeight * 36 / 46, paint); //图片相对位置
}

private float getAngle(float db) {
    return (db - 85) * 5 / 3;

}
}