xml file. During compilation, each element in the XML is compiled into equivalent Android GUI class with attributes represented by methods. • View: A View is just a widget that appears on the screen. It could be textview, editText, button etc., • ViewGroups: A ViewGroup is a special view that can contain other views.The view group is the base class for layouts and views containers.Eg: Relative layout,Linear layout etc., • XML attributes: Every View and ViewGroup object supports their own variety of XML attributes.It is used to specify and set property to the Views and ViewGroups.Like width, height, padding, margin and size etc., • Measurement units: For layout, measurement units will be represent in dp (Density-independent Pixels) and for font unit is sp (Scale-independent Pixels).