How to: Declare Enumerations (Visual Basic)

Статья
02/04/2013

You create an enumeration with the Enum statement in the declarations section of a class or module. You cannot declare an enumeration within a method. To specify the appropriate level of access, use Private, Protected, Friend, or Public.

An Enum type has a name, an underlying type, and a set of fields, each representing a constant. The name must be a valid Visual Basic 2005 qualifier. The underlying type must be one of the integer types—Byte, Short, Long or Integer. Integer is the default. Enumerations are always strongly typed and are not interchangeable with integer number types.

Enumerations cannot have floating-point values. If an enumeration is assigned a floating-point value with Option Strict On, a compiler error results. If Option Strict is Off, the value is automatically converted to the Enum type.

For information on names, and how to use the Imports statement to make name qualification unnecessary, see Enumerations and Name Qualification (Visual Basic).

To declare an enumeration

Write a declaration that includes a code access level, the Enum keyword, and a valid name, as in the following examples, each of which declares a different Enum.

Private Enum SampleEnum
        SampleMember
    End Enum
    Public Enum SampleEnum2
        SampleMember
    End Enum
    Protected Enum SampleEnum3
        SampleMember
    End Enum
    Friend Enum SampleEnum4
        SampleMember
    End Enum
    Protected Friend Enum SampleEnum5
        SampleMember
    End Enum

Define the constants in the enumeration. By default, the first constant in an enumeration is initialized to 0, and subsequent constants are initialized to a value of one more than the previous constant. For example, the following enumeration, Days, contains a constant named Sunday with the value 0, a constant named Monday with the value 1, a constant named Tuesday with the value of 2, and so on.
```
Public Enum Days
  Sunday
  Monday
  Tuesday
  Wednesday
  Thursday
  Friday
  Saturday
End Enum
```
You can explicitly assign values to constants in an enumeration by using an assignment statement. You can assign any integer value, including negative numbers. For example, you may want constants with values less than zero to represent error conditions. In the following enumeration, the constant Invalid is explicitly assigned the value –1, and the constant Sunday is assigned the value 0. Because it is the first constant in the enumeration, Saturday is also initialized to the value 0. The value of Monday is 1 (one more than the value of Sunday); the value of Tuesday is 2, and so on.
```
Public Enum WorkDays
  Saturday
  Sunday = 0
  Monday
  Tuesday
  Wednesday
  Thursday
  Friday
  Invalid = -1
End Enum
```

To declare an enumeration as an explicit type

Specify the type of the enum by using the As clause, as shown in the following example.
```
Public Enum MyEnum As Byte
  Zero
  One
  Two
End Enum
```

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How to: Declare Enumerations (Visual Basic)

To declare an enumeration

To declare an enumeration as an explicit type

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