Flags, Enum. Sometimes an Enum may have multiple values set at the same time: in VB.NET, the Flags attribute can help for this purpose. We can set, and remove, individual flags.
With the HasFlag function, we can determine if a flag is set. With bitwise operators like Or and And, we can set (and remove) flags on the Enum instance.
Example. This VB.NET program uses a custom FileAttributes Enum and sets flags on it. Notice how the enum uses powers of 2 for the values—this enables flags to be set without issues.
Step 1 We create a new instance of the FileAttributes Enum. We use an "Or" expression to set two flags at once.
Step 2 We use the HasFlag Function to test if the Current attribute is set on FileAttributes.
Step 3 To determine if a flag is not set, we can use Not with the HasFlag Function.
Step 4 It is possible to remove a flag that has been set by using the VB.NET And Not operators.
Step 5 By calling HasFlag again, after the enum value was modified, we can see that it correctly tests the presence of a flag.
<Flags>
Enum FileAttributes
None = 0
Cached = 1
Current = 2
Obsolete = 4
End Enum
Module Module1
Sub Main()
' Step 1: new enum instance.
Console.WriteLine("SET CACHED AND CURRENT FLAGS")
Dim attributes As FileAttributes = FileAttributes.Cached Or FileAttributes.Current
' Step 2: check Current flag.
If attributes.HasFlag(FileAttributes.Current)
Console.WriteLine("... File is current")
End If
' Step 3: check Obsolete flag.
If Not attributes.HasFlag(FileAttributes.Obsolete)
Console.WriteLine("... File is not obsolete")
End If
' Step 4: remove Current flag from instance.
Console.WriteLine("REMOVE CURRENT FLAG")
attributes = attributes And Not FileAttributes.Current
' Step 5: check Current flag again.
If Not attributes.HasFlag(FileAttributes.Current)
Console.WriteLine("... File is not current")
End If
End Sub
End ModuleSET CACHED AND CURRENT FLAGS
... File is current
... File is not obsolete
REMOVE CURRENT FLAG
... File is not current
Summary. With Enum and the Flags attribute, we can set multiple enum values at the same time. The Flags attribute works like a "bit flag" where each bit represents a boolean value.
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