Enum.Parse. Sometimes a String must be converted into an Enum. This requires a special Function call. In VB.NET we use the Enum.Parse, or TryParse, Functions.
Method notes. We handle exceptions and errors for each method. Often TryParse is a better choice if our data is not already validated.
First example. This example introduces an Enum of name PetType. In the Main Sub, we have a String literal with value "Dog". We call [Enum].Parse to get its same-named Enum.
Info The GetType Function is used with the argument VehicleType. This is the Type argument to the Enum.Parse Function.
Important The Enum type uses a special syntax where it is surrounded by square brackets. This indicates a Type, not the Enum keyword.
Module Module1
''' <summary>
''' Types of pets.
''' </summary>
Enum PetType
None
Cat
Dog
End Enum
Sub Main()
' Convert String to Enum.
Dim value As String = "Dog"
Dim type As PetType = [Enum].Parse(GetType(PetType), value)
' Test Enum.
If type = PetType.Dog Then
Console.WriteLine("Equals dog")
End If
End Sub
End ModuleEquals dog
Example 2. Next, we learn that Enum.Parse will throw an Exception on an invalid String. One way to handle this problem is to use a Try-Catch block to capture possible errors.
Module Module1
Enum VehicleType
None
Truck
Sedan
Coupe
End Enum
Sub Main()
' An invalid String.
Dim value As String = "Spaceship"
Try
' Parse the invalid String.
Dim type As VehicleType = [Enum].Parse(GetType(VehicleType), value)
Catch ex As Exception
' Write the Exception.
Console.WriteLine(ex)
End Try
End Sub
End ModuleSystem.ArgumentException: Requested value 'Spaceship' was not found.
at System.Enum.EnumResult.SetFailure...
TryParse. Next, the TryParse Function is available. It handles errors in a safer, faster way. It does not throw an Exception on an invalid String that cannot be converted.
Return Enum.TryParse returns False if the string cannot be converted. The Enum is set to the default value.
Module Module1
Enum VehicleType
None
Truck
Sedan
End Enum
Sub Main()
' An invalid String.
Dim value As String = "Starship"' Parse the invalid String.
Dim result As VehicleType
[Enum].TryParse(value, result)
' It is the default.
Console.WriteLine(result.ToString())
End Sub
End ModuleNone
A summary. We require no custom conversion methods to parse Enums in VB.NET programs. Instead, the Enum.Parse and TryParse Functions fill this need.
Final notes. If an invalid String may be encountered, the TryParse Function is often superior. Avoiding exceptions is faster in most programs.
Dot Net Perls is a collection of pages with code examples, which are updated to stay current. Programming is an art, and it can be learned from examples.
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This page was last updated on Aug 1, 2024 (edit link).