[Android] ViewRoot and View class

> 1.  what is the relationship between ViewRoot and View class.

The ViewRoot is the root of each view hierarchy. Like you said, there
is one ViewRoot per window. The ViewRoot is responsible to handling
the layout and drawing of the view hierarchy. The view hierarchy is
made of Views and ViewGroups. A ViewGroup is a special View that can
contain other Views.

> Is all view ,its children's view and their viewRoot share the same
> canvas for draw?

Yes, but that Canvas might change on every drawing operation. The
ViewRoot acquires a Canvas from the underlying Surface and hands that
Canvas to the top-level View.

> 2. What is the relationship within View, canvas and Surface.  To my
> thinking, every view will be attached a canvas and surface.

No, the Views are not attached to the Canvas nor the Surface. The
window is tied to a Surface and the ViewRoot asks the Surface for a
Canvas that is then used by the Views to draw onto.

> canvas hold the bitmap for view, will the actual view drawn data
will
> be in canvas' bitmap.

Yes.

> After View draw its data to canvas, ViewRoot
> will call surface.unlockCanvasAndPost(canvas) to schedule
> surfaceFlinger::composeSurfaces() which do the actually display to
> display panel.

Yes.

> Where is the drawn data in canvas transfer to surface front buffer
or
> backbuffer? I cannot find the code to do that.

It's done by SurfaceFlinger.

> Do different views within the same ViewRoot share the same surface?

Yes, except for SurfaceViews.