Android获取两条线之间的夹角度数

 /**
     *获取两条线的夹角
     * @param centerX
     * @param centerY
     * @param xInView
     * @param yInView
     * @return
     */
    public static int getRotationBetweenLines(float centerX, float centerY, float xInView, float yInView) {
        double rotation = 0;

        double k1 = (double) (centerY - centerY) / (centerX * 2 - centerX);
        double k2 = (double) (yInView - centerY) / (xInView - centerX);
        double tmpDegree = Math.atan((Math.abs(k1 - k2)) / (1 + k1 * k2)) / Math.PI * 180;

        if (xInView > centerX && yInView < centerY) {  //第一象限
            rotation = 90 - tmpDegree;
        } else if (xInView > centerX && yInView > centerY) //第二象限
        {
            rotation = 90 + tmpDegree;
        } else if (xInView < centerX && yInView > centerY) { //第三象限
            rotation = 270 - tmpDegree;
        } else if (xInView < centerX && yInView < centerY) { //第四象限
            rotation = 270 + tmpDegree;
        } else if (xInView == centerX && yInView < centerY) {
            rotation = 0;
        } else if (xInView == centerX && yInView > centerY) {
            rotation = 180;
        }

        return (int) rotation;
    }

 @Override
    public boolean onTouch(View v, MotionEvent event) {
        float centerX = img_colors.getWidth() / 2;
        float centerY = img_colors.getHeight() / 2;
        setPointerRotation(Tools.getRotationBetweenLines(centerX, centerY, event.getX(), event.getY()));
        return true;
    }