# 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 * [Material Design guidelines: App Bars](https://material.io/guidelines/layout/structure.html#structure-app-bar) * [Material Design guidelines: Scrolling techniques](https://material.io/guidelines/patterns/scrolling-techniques.html) * [Class definition](https://github.com/material-components/material-components-android/tree/master/lib/java/android/support/design/widget/AppBarLayout.java) * [Class overview](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.html) As a container for Toolbars, and other views, it works with [CoordinatorLayout](https://developer.android.com/reference/android/support/design/widget/CoordinatorLayout.html) 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](https://developer.android.com/reference/android/support/v4/widget/NestedScrollView.html), [RecyclerView](https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html)). 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:** * [enterAlways](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.LayoutParams.html#SCROLL_FLAG_ENTER_ALWAYS) * [enterAlwaysCollapsed](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.LayoutParams.html#SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED) * [exitUntilCollapsed](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.LayoutParams.html#SCROLL_FLAG_EXIT_UNTIL_COLLAPSED) * [scroll](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.LayoutParams.html#SCROLL_FLAG_SCROLL) * [snap](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.LayoutParams.html#SCROLL_FLAG_SNAP) * [snapMargins](https://developer.android.com/reference/android/support/design/widget/AppBarLayout.LayoutParams.html#SCROLL_FLAG_SNAP_MARGINS) 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 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](https://developer.android.com/reference/android/support/v7/app/AppCompatActivity.html#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. * [App bar](https://material.io/guidelines/layout/structure.html#structure-app-bar) * [Toolbars](https://material.io/guidelines/components/toolbars.html#toolbars-usage) * [CollapsingToolbarLayout](CollapsingToolbarLayout.md)