图片旋转

Bitmap  bitmap=((BitmapDrawable)getResources().getDrawable(R.drawable.pull_down_color)).getBitmap();           
Matrix matrix=new Matrix();
        matrix.postRotate(180);
        bitmap=Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
        iv_dow.setImageBitmap(bitmap);