Android图片旋转到固定方向方法

/**
* 旋转bitmap
*
* @param imageView 要显示旋转后的图片
* @param bitmap    要旋转的图片，方向向上
* @param rotate    旋转的大小(一个圆360°被分为16份，rotate的值为0-15，图片向上时rotate为0)
*/
private void rotateBitmap(ImageView imageView, Bitmap bitmap, int rotate) {
Matrix matrix = new Matrix();
float n = (float) 360 / 16 * rotate;
int r0 = bitmap.getWidth() / 2;
matrix.preRotate(n, r0, r0);
bitmap = Bitmap.createBitmap(bitmap, 0, 0, 2 * r0, 2 * r0, matrix, true);
int r1 = bitmap.getWidth() / 2;
bitmap = Bitmap.createBitmap(bitmap, r1 - r0, r1 - r0, 2 * r0, 2 * r0);
imageView.setImageBitmap(bitmap);
imageView.setVisibility(View.VISIBLE);
}