CA2217: Do not mark enums with FlagsAttribute

Cause

An externally visible enumeration is marked with FlagsAttribute and it has one or more values that are not powers of two or a combination of the other defined values on the enumeration.

Rule Description

An enumeration should have FlagsAttribute present only if each value defined in the enumeration is a power of two, or a combination of defined values.

How to Fix Violations

To fix a violation of this rule, remove FlagsAttribute from the enumeration.

When to Suppress Warnings

Do not suppress a warning from this rule.

Example

The following example shows an enumeration, Color, that contains the value 3, which is neither a power of two, nor a combination of any of the defined values. The Color enumeration should not be marked with the FlagsAttribute.

Imports System

Namespace Samples

    ' Violates this rule    
    <FlagsAttribute()> _
    Public Enum Color

        None = 0
        Red = 1
        Orange = 3
        Yellow = 4

    End Enum 
End Namespace

using System;

namespace Samples
{    
    // Violates this rule    
    [FlagsAttribute]        
    public enum Color
    { 
        None    = 0, 
        Red     = 1, 
        Orange  = 3, 
        Yellow  = 4 
    }
}

using namespace System;

namespace Samples 
{
    // Violates this rule    
    [FlagsAttribute]    
    public enum class Color    
    {        
        None   = 0,        
        Red    = 1,        
        Orange = 3,        
        Yellow = 4    
    };
}

The following example shows an enumeration, Days, that meets the requirements for being marked with the System.FlagsAttribute.

Imports System
Namespace Samples

    <FlagsAttribute()> _
    Public Enum Days

        None = 0
        Monday = 1
        Tuesday = 2
        Wednesday = 4
        Thursday = 8
        Friday = 16
        All = Monday Or Tuesday Or Wednesday Or Thursday Or Friday

    End Enum 
End Namespace

using System;

namespace Samples
{    
    [FlagsAttribute]    
    public enum Days    
    {        
        None        = 0,        
        Monday      = 1,        
        Tuesday     = 2,        
        Wednesday   = 4,        
        Thursday    = 8,        
        Friday      = 16,        
        All         = Monday| Tuesday | Wednesday | Thursday | Friday    
    }
}

using namespace System;

namespace Samples 
{    
    [FlagsAttribute]    
    public enum class Days    
    {        
        None        = 0,        
        Monday      = 1,        
        Tuesday     = 2,        
        Wednesday   = 4,        
        Thursday    = 8,        
        Friday      = 16,        
        All         = Monday| Tuesday | Wednesday | Thursday | Friday    
    };
}

Related Rules

CA1027: Mark enums with FlagsAttribute

See Also

Reference

System.FlagsAttribute