Transparent surfaceview on top of Toolbar

Question

I’m drawing a graph, and for that I’m using a Class that extends from SurfaceView.

The screen where it will be drawn has a background image. So that the SurfaceView be transparent, I did the following:

 setBackgroundColor(Color.TRANSPARENT);
 setZOrderOnTop(true);
 surfaceHolder = getHolder();
 surfaceHolder.setFormat(PixelFormat.TRANSPARENT);

It worked! the area of SurfaceView was transparent, but when I give the scroll on the screen, the SurfaceView is over the Toolbar.

I believe it is due to the following line:

setZOrderOnTop(true);

But if removed, or Seto as false the background turns black!

How can I leave a SurfaceView transparent and maintain the Z below the Toolbar?