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An Enum type stores special values. These are named constants. With an Enum type we can remove magic constants throughout our program. And this improves code clarity. It makes the program easier to maintain.
First we look at a Module that uses an Enum named Importance. The Enum represents a constant value that tells how important the value is. The names of the constants in an Enum type can be changed to any valid identifiers.
Next:In the Main method, we use a Select statement on an enum variable. This enables a fast match for the correct Enum value.
Based on: .NET 4.0 Program that uses Enum with Select: VB.NET Module Module1 ''' <summary> ''' Levels of importance. ''' </summary> Enum Importance Critical = 4 Important = 3 None = 0 Regular = 2 Trivial = 1 End Enum Sub Main() Dim value As Importance = Importance.Critical ' Select the enum and print a value. Select Case value Case Importance.Trivial Console.WriteLine("Not true") Return Case Importance.Critical Console.WriteLine("True") Exit Select End Select End Sub End Module Output True
Often you will use the If and ElseIf constructs to implement checks for certain Enum values. The If and ElseIf statements are only useful for when you are checking an Enum Dim variable against certain named constants in that Enum type.If Then
Here:We represent a markup tag, such as HTML, in a conceptual model as an Enum value. We test the tags with the If and ElseIf statements.
Program that uses enum If and ElseIf: VB.NET Module Module1 ''' <summary> ''' Represents tag type. ''' </summary> Enum TagType BoldTag = 1 HyperlinkTag = 3 ItalicsTag = 2 None = 0 End Enum Sub Main() ' Create enum type variable. Dim value As TagType = TagType.HyperlinkTag ' Use enum in If-statement. ' ... Also use ElseIf statement. If value = TagType.BoldTag Then Console.WriteLine("Bold") ElseIf value = TagType.HyperlinkTag Then Console.WriteLine("Not true") End If End Sub End Module Output Not true
We need to invoke ToString explicitly on the Enum variable when you pass it to the Console.Write or WriteLine subs. If you do not call ToString, you will receive the numeric value of the enum, not the string representation.
In this example, we demonstrate the ToString method on the Enum variable type.
The Enum represents a type of animal,
which contains options for cats
and dogs. We finally call Console.WriteLine.
Program that uses enum and ToString: VB.NET Module Module1 ''' <summary> ''' Type of animal. ''' </summary> Enum AnimalType Cat = 1 Dog = 2 None = 0 End Enum ''' <summary> ''' Type of visibility. ''' </summary> Enum VisibilityType Hidden = 2 None = 0 Visible = 4 End Enum Sub Main() Dim dog As AnimalType = AnimalType.Dog Dim hidden As VisibilityType = VisibilityType.Hidden ' Write to the Console with the ToString method. Console.WriteLine(dog.ToString) Console.WriteLine(hidden.ToString) End Sub End Module Output Dog Hidden
Here we use a Stack collection to represent a markup tree. If you have an HTML document with bold tags, hyperlink tags, and italics tags, you could use a Stack of Enum values (TagType) to represent to markup tree.
Note:You could use this functionality for HTML validation as well. Opening and closing tags could be matched.
Tip:To use the Stack collection, you typically use the Push, Pop, as well as Peek methods.Stack
Program that uses enum, Stack: VB.NET Module Module1 Enum TagType BoldTag = 1 HyperlinkTag = 3 ItalicsTag = 2 None = 0 End Enum Sub Main() ' Create a new Stack generic instance. Dim stack As New Stack(Of TagType) ' Add a BoldTag to it. stack.Push(TagType.BoldTag) ' Add an ItalicsTag to it. stack.Push(TagType.ItalicsTag) ' Pop the top element. ' ... Then write it to the Console. Dim popped As TagType = stack.Pop() Console.WriteLine(popped) Console.WriteLine(popped.ToString) End Sub End Module Output 2 ItalicsTag
If you have a String value that contains an Enum name, how can you convert it to an Enum value? The Enum.Parse and Enum.TryParse functions are available for this purpose. We test them in example programs.Enum.Parse, TryParse
We dived into the basics of the Enum type in the VB.NET language. We saw how it can be used to represent a set of named constants. Typically these named constants represent a selection of options for a specific variable.
And:They are used throughout the VB.NET program as symbolic constants. This improves the clarity of the code.