How does findViewById initialise a view

Question

I just wrote an answer for someone confused by findViewById and I realised that I have a gap in my understanding. This question is for knowledge and curiosity only.

Consider this:

button = (Button)findViewById(R.id.button);

findViewById returns an instance of View, which is then cast to the target class. All good so far.

To setup the view, findViewById constructs an AttributeSet from the parameters in the associated XML declaration which it passes to the constructor of View.

We then cast the View instance to Button.

How does the AttributeSet get passed in turn to the Button constructor?

[EDIT]

So I was the confused one :). The whole point is that when the layout is inflated, the view hierarchy already contains an instance of the view descendant class. findViewById simply returns a reference to it. Obvious when you think about it - doh..

Answer 1

findViewById does nothing. It just looks through view hierarchy and returns reference to a view with requested viewId. View is already created and exists. If you do not call findViewById for some view nothing changes.

Views are inflated by LayoutInflator. When you call setContentView xml layout is parsed and view hierarchy is created.

attributes passed to Button's constructor by LayoutInflater. check LayoutInflator source code.