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Follows these rules: Title is the Component Name as it appears in spec. Justification: Formatting and display on small width screens. Excerpt includes the CamelCase name of the java class. Justification: This document is not a rehash of spec, it's a specific resource for Android devs. Title and excerpt are displayed in the same context. Header is the CamelCase name of the java class. Justification: Similar to excerpt. This is documentation on a specific Android widget. Path is the dash-deliminated name of the java class. Justification: Similar to header. This is documentation on a specific Android widget. PiperOrigin-RevId: 155134932
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AppBarLayout
AppBarLayout is a ViewGroup used to wrap the app bar that provides many of the Material Design features and interactions for the app bar, namely responsiveness to scrolling.
Design & API Documentation
As a container for Toolbars, and other views, it works with CoordinatorLayout 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. NestedScrollView, RecyclerView).
Flags are added to each child of the AppBarLayout to control how they will respond to scrolling. These are interpreted by the AppBarLayout.LayoutParams.
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.
Related Concepts
The 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 app bar. They are programatically identical and use the Toolbar class.
The 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 app bar.
A CollapsingToolbarLayout is often used as a wrapper around the Toolbar to provide additional UI features in relation to scrolling.