为什么 Toolbar 取代了 ActionBar？
Why did Toolbar replace ActionBar?
从 Android L 开始，我们有一个 Toolbar 而不是 ActionBar，尽管它的用法看起来是一样的。他们甚至通过支持库恢复了 Toolbar 的兼容性。
他们用 Toolbar 替换 ActionBar 的原因是什么？
添加工具栏是因为 UI 已经超越了 ActionBar 的限制。主要区别在于，工具栏可以从 Activity 的不透明 window 装饰中分离出来，并放置在您的自定义布局中的某个地方。从那里，您可以自由地使用工具栏做一些更有趣的事情。一个常见的例子是根据滚动增加或缩小高度。
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 setActionBar() 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.
从 Android L 开始，我们有一个 Toolbar 而不是 ActionBar，尽管它的用法看起来是一样的。他们甚至通过支持库恢复了 Toolbar 的兼容性。
他们用 Toolbar 替换 ActionBar 的原因是什么？
添加工具栏是因为 UI 已经超越了 ActionBar 的限制。主要区别在于，工具栏可以从 Activity 的不透明 window 装饰中分离出来，并放置在您的自定义布局中的某个地方。从那里，您可以自由地使用工具栏做一些更有趣的事情。一个常见的例子是根据滚动增加或缩小高度。
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 setActionBar() 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.