A standard toolbar for use within application content.
A Toolbar is a generalization of action bars for use
within application layouts. While an action bar is traditionally part of an
Activity's opaque window decor controlled by the framework,
a Toolbar may be placed at any arbitrary level of nesting within a view hierarchy.
An application may choose to designate a Toolbar as the action bar for an Activity
using the setSupportActionBar() method.
Toolbar supports a more focused feature set than ActionBar. From start to end, a toolbar
may contain a combination of the following optional elements:
A navigation button. This may be an Up arrow, navigation menu toggle, close,
collapse, done or another glyph of the app's choosing. This button should always be used
to access other navigational destinations within the container of the Toolbar and
its signified content or otherwise leave the current context signified by the Toolbar.
The navigation button is vertically aligned within the Toolbar's minimum height,
if set.
A branded logo image. This may extend to the height of the bar and can be
arbitrarily wide.
A title and subtitle. The title should be a signpost for the Toolbar's current
position in the navigation hierarchy and the content contained there. The subtitle,
if present should indicate any extended information about the current content.
If an app uses a logo image it should strongly consider omitting a title and subtitle.
One or more custom views. The application may add arbitrary child views
to the Toolbar. They will appear at this position within the layout. If a child view's
Toolbar.LayoutParams indicates a Gravity value of
CENTER_HORIZONTAL the view will attempt to center
within the available space remaining in the Toolbar after all other elements have been
measured.
An action menu. The menu of actions will pin to the
end of the Toolbar offering a few
frequent, important or typical actions along with an optional overflow menu for
additional actions. Action buttons are vertically aligned within the Toolbar's
minimum height, if set.
In modern Android UIs developers should lean more on a visually distinct color scheme for
toolbars than on their application icon. The use of application icon plus title as a standard
layout is discouraged on API 21 devices and newer.
