Gets the zero-based index of the currently visible child container.
Child indexes are in the range 0, 1, 2, ..., n - 1, where n is the number of children. The default value is 0, corresponding to the first child. If there are no children, the value of this property is -1.
Note: When you add a new child to a ViewStack container, the selectedIndex property is automatically adjusted, if necessary, so that the selected child remains selected.
protected Integer selectedIndex { get; }
'Declaration
Protected Read Property selectedIndex As Integer