创建一个定制类，使其名称与枚举名称相同。

Create a custom class with the same name as the enumeration name.

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为枚举中的每项创建一个Const全局变量，各Const的名称都以枚举名称开头，后接下划线(在本例中为BookType_xxx)。

Create a global Const variable for each item in the enumeration with each Const name starting with the enumeration name followed by an underscore (in our case, BookType_xxx).

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创建一个全局列表，使其数据类型等同于枚举名称，且名称以enum _开头，后接枚举名称(在本例中为Enum_BookType)。

Create a global list with a data type equal to the enumeration name and with a name of Enum_ followed by the enumeration name (in our case, Enum_BookType).

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