（更新中）Android3.0——ActionBar

（更新中,有的直接是api中搬来）ActionBar

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1. ActionBar的用途

• App icon
  • The app icon establishes your app's identity. It can be replaced with a different logo or branding if you wish. Important: If the app is currently not displaying the top-level screen, be sure to display the Up caret to the left of the app icon, so the user can navigate up the hierarchy. For more discussion of Up navigation, see the Navigation pattern.

• View control
  
  • If your app displays data in different views, this segment of the action bar allows users to switch views. Examples of view-switching controls are drop-down menus or tab controls. For more information on view-switching, see the App Structure pattern.
  • If your app doesn't support different views, you can also use this space to display non-interactive content, such as an app title or longer branding information.
    

• Action buttons
  
  • Show the most important actions of your app in the actions section. Actions that don't fit in the action bar are moved automatically to the action overflow. Long-press on an icon to view the action's name.
• Action overflow
  • Move less often used actions to the action overflow.