Top App Bars
AppBarLayout is a ViewGroup, most commonly used to wrap a
Toolbar, that provides
many of the Material Design features and interactions for Top App Bars, namely
responsiveness to scrolling.
Design & API Documentation
As a container for Toolbars, and other views, it works with
in order to respond to scrolling techniques.
AppBarLayout depends heavily on
being used as a direct child of the CoordinatorLayout and reacts to a sibling
that supports scrolling (e.g.
Flags are added to each child of the
AppBarLayout to control how they will
respond to scrolling. These are interpreted by the
Available flags are:
Views using the scroll flag should be declared and visually positioned before
other views in the
AppBarLayout. This ensures that they are able to exit at the
top of the screen, leaving behind fixed, or pinned, elements.
Lift On Scroll
Top App Bars can also be fixed in place and positioned at the same elevation as
content. Upon scroll, they can increase elevation and let content scroll behind
them. This design pattern is called “Lift On Scroll” and can be implemented by
app:liftOnScroll="true" on your
liftOnScroll attribute requires that you apply the
layout_behavior to your scrolling
The Top App Bar is a way of referencing a specific type of Toolbar. It’s not a separate Android class. This UI element is often used to provide branding for the app as well as a place to handle common actions like navigation, search, and menus. These are accessible via text or buttons in the Toolbar. A Toolbar that provides some of these features is often referred to as the Top App Bar. They are programmatically identical and use the Toolbar class.
The Top App Bar was previously termed action bar, and there are methods that utilize this name (e.g. getSupportActionBar). Other than use of the action bar APIs, references to this prominent Toolbar element should be Top App Bar.
A CollapsingToolbarLayout is often used as a wrapper around the Toolbar to provide additional UI features in relation to scrolling.