Android Layouts [UPADTED 2019]
A layout defines the structure for a user interface in your app, such as in an activity. All elements in the layout are built using a hierarchy of View and ViewGroup objects. A View usually draws something the user can see and interact with. Whereas a ViewGroup is an invisible container that defines the layout structure for View and other ViewGroup objects, as shown in figure 1. Figure 1. Illustration of a view hierarchy, which defines a UI layout The View objects are usually called "widgets" and can be one of many subclasses, such as Button or TextView . The ViewGroup objects are usually called "layouts" can be one of many types that provide a different layout structure, such as LinearLayout or ConstraintLayout . You can declare a layout in two ways: Declare UI elements in XML . Android provides a straightforward XML vocabulary that corresponds to the View classes and subclasses, such as those for widgets and layouts. You can also use Android ...