two views with same id

Question

How does android use R.id.id_name to find views after inflating the XML?

1.Suppose I have two XML\'s with one button each with same id.

2.I have

Answer 1

Android takes the easy road: IDs are not application-wide unique, but layout-wide unique.

The value of R.id.foo is the same across two different layouts holding a control with foo id. Since they are not competing for uniqueness, it doesn't matter.

Answer 2

It knows which View should it use, because it looks for View with this specific id in a XML file that is currently set as content view (or is inflated).

Answer 3

The ID is not a unique reference.

However, in practice, you differentiate by using the parent view.

If we consider that 'this' is an Activity, set up with a layout that contains your buttons, then:

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

will return the first one it finds in the layout (I think - not sure the actual behaviour is defined).

However what you might do is call findViewById on some parent view that contains only one such instance with that ID.

LinearLayout okParent = (LinearLayout) this.findViewById( R.id.okLayout );
LinearLayout cancelParent = (LinearLayout) this.findViewById( R.id.cancelLayout );

Button okButton = (Button) okParent.findViewById( R.id.id_name );
Button cancelButton = (Button) cancelParent.findViewById( R.id.id_name );

Conceptually, this is a sort of path based lookup. You should be careful to design your layouts such that this is possible.