出于安全原因，iPhone OS将应用程序(包括其首选项和数据)限制为文件系统中的唯一位置.此限制是安全功能(称为应用程序的沙箱")的一部分.沙箱是一组细粒度的控件，它们限制了应用程序对文件，首选项，网络资源，硬件等的访问.在iPhone OS中，应用程序及其数据驻留在其他应用程序无法访问的安全位置.安装应用程序后，系统会为该应用程序计算一个唯一的不透明标识符.系统使用根应用程序目录和此标识符来构造到应用程序主目录的路径.因此，应用程序的主目录可以描述为具有以下结构:

For security reasons, iPhone OS restricts an application (including its preferences and data) to a unique location in the file system. This restriction is part of the security feature known as the application’s "sandbox." The sandbox is a set of fine-grained controls limiting an application’s access to files, preferences, network resources, hardware, and so on. In iPhone OS, an application and its data reside in a secure location that no other application can access. When an application is installed, the system computes a unique opaque identifier for the application. Using a root application directory and this identifier, the system constructs a path to the application’s home directory. Thus an application’s home directory could be depicted as having the following structure:

  /ApplicationRoot/ApplicationID/

在安装过程中，系统会创建应用程序的主目录和几个关键子目录，配置应用程序沙箱，然后将应用程序捆绑包复制到主目录.对每个应用程序及其数据使用唯一的位置可简化备份和还原操作，应用程序更新和卸载.有关为每个应用程序创建的特定于应用程序的目录以及应用程序更新以及备份和还原操作的更多信息.

During the installation process, the system creates the application’s home directory and several key subdirectories, configures the application sandbox, and copies the application bundle to the home directory. The use of a unique location for each application and its data simplifies backup-and-restore operations, application updates, and uninstallation. For more information about the application-specific directories created for each application and about application updates and backup-and-restore operations.

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