Enum Class
Updated: June 2010
Provides the base class for enumerations.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
The Enum type exposes the following members.
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CompareTo | Compares this instance to a specified object and returns an indication of their relative values. |
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Equals | Returns a value indicating whether this instance is equal to a specified object. (Overrides ValueType.Equals(Object).) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.) |
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GetHashCode | Returns the hash code for the value of this instance. (Overrides ValueType.GetHashCode().) |
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GetName | Retrieves the name of the constant in the specified enumeration that has the specified value. |
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GetNames | Retrieves an array of the names of the constants in a specified enumeration. |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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GetTypeCode | Returns the underlying TypeCode for this instance. |
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GetUnderlyingType | Returns the underlying type of the specified enumeration. |
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GetValues | Retrieves an array of the values of the constants in a specified enumeration. |
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HasFlag | Determines whether one or more bit fields are set in the current instance. |
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IsDefined | Returns an indication whether a constant with a specified value exists in a specified enumeration. |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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Parse | Converts the string representation of the name or numeric value of one or more enumerated constants to an equivalent enumerated object. A parameter specifies whether the operation is case-insensitive. |
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ToObject | Returns an instance of the specified enumeration set to the specified value. |
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ToString() | Converts the value of this instance to its equivalent string representation. (Overrides ValueType.ToString().) |
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ToString(IFormatProvider) | Obsolete. This method overload is obsolete; use Enum.ToString(). |
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ToString(String) | Converts the value of this instance to its equivalent string representation using the specified format. |
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ToString(String, IFormatProvider) | Obsolete. This method overload is obsolete; use Enum.ToString(String). |
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TryParse<TEnum>(String, TEnum) | Converts the string representation of the name or numeric value of one or more enumerated constants to an equivalent enumerated object. The return value indicates whether the conversion succeeded. |
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TryParse<TEnum>(String, Boolean, TEnum) | Converts the string representation of the name or numeric value of one or more enumerated constants to an equivalent enumerated object. A parameter specifies whether the operation is case-sensitive. The return value indicates whether the conversion succeeded. |
| Name | Description | |
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IConvertible.ToBoolean | Infrastructure. Converts the current value to a Boolean value based on the underlying type. |
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IConvertible.ToByte | Infrastructure. Converts the current value to an 8-bit unsigned integer based on the underlying type. |
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IConvertible.ToChar | Infrastructure. Converts the current value to a Unicode character based on the underlying type. |
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IConvertible.ToDateTime | Infrastructure. Converts the current value to a DateTime based on the underlying type. |
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IConvertible.ToDecimal | Infrastructure. Converts the current value to a Decimal based on the underlying type. |
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IConvertible.ToDouble | Infrastructure. Converts the current value to a double-precision floating point number based on the underlying type. |
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IConvertible.ToInt16 | Infrastructure. Converts the current value to a 16-bit signed integer based on the underlying type. |
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IConvertible.ToInt32 | Infrastructure. Converts the current value to a 32-bit signed integer based on the underlying type. |
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IConvertible.ToInt64 | Infrastructure. Converts the current value to a 64-bit signed integer based on the underlying type. |
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IConvertible.ToSByte | Infrastructure. Converts the current value to an 8-bit signed integer based on the underlying type. |
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IConvertible.ToSingle | Infrastructure. Converts the current value to a single-precision floating point number based on the underlying type. |
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IConvertible.ToType | Infrastructure. Converts the current value to a specified type based on the underlying type. |
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IConvertible.ToUInt16 | Infrastructure. Converts the current value to a 16-bit unsigned integer based on the underlying type. |
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IConvertible.ToUInt32 | Infrastructure. Converts the current value to a 32-bit unsigned integer based on the underlying type. |
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IConvertible.ToUInt64 | Infrastructure. Converts the current value to a 64-bit unsigned integer based on the underlying type. |
An enumeration is a named constant whose underlying type is any integral type except Char. If no underlying type is explicitly declared, Int32 is used. Programming languages typically provide syntax to declare an enumeration that consists of a set of named constants and their values.
Caution:
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You should never create an enumeration type whose underlying type is non-integral. Although you can create such a type by using reflection, method calls that use the resulting type are unreliable and may also throw additional exceptions. |
Enum provides methods to compare instances of this class, convert the value of an instance to its string representation, convert the string representation of a number to an instance of this class, and create an instance of a specified enumeration and value.
You can also treat an enumeration as a bit field. For more information, see FlagsAttribute.
Implemented Interfaces
This class inherits from ValueType, and implements the IComparable, IFormattable, and IConvertible interfaces. Use the Convert class for conversions instead of this class' explicit interface member implementation of IConvertible.
Guidelines for FlagsAttribute and Enum
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Use the FlagsAttribute custom attribute for an enumeration only if a bitwise operation (AND, OR, EXCLUSIVE OR) is to be performed on a numeric value.
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Define enumeration constants in powers of two, that is, 1, 2, 4, 8, and so on. This means the individual flags in combined enumeration constants do not overlap.
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Consider creating an enumerated constant for commonly used flag combinations. For example, if you have an enumeration used for file I/O operations that contains the enumerated constants Read = 1 and Write = 2, consider creating the enumerated constant ReadWrite = Read OR Write, which combines the Read and Write flags. In addition, the bitwise OR operation used to combine the flags might be considered an advanced concept in some circumstances that should not be required for simple tasks.
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Use caution if you define a negative number as a flag enumerated constant because many flag positions might be set to 1, which might make your code confusing and encourage coding errors.
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A convenient way to test whether a flag is set in a numeric value is to perform a bitwise AND operation between the numeric value and the flag enumerated constant, which sets all bits in the numeric value to zero that do not correspond to the flag, then test whether the result of that operation is equal to the flag enumerated constant.
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Use None as the name of the flag enumerated constant whose value is zero. You cannot use the None enumerated constant in a bitwise AND operation to test for a flag because the result is always zero. However, you can perform a logical, not a bitwise, comparison between the numeric value and the None enumerated constant to determine whether any bits in the numeric value are set.
If you create a value enumeration instead of a flags enumeration, it is still worthwhile to create a None enumerated constant. The reason is that by default the memory used for the enumeration is initialized to zero by the common language runtime. Consequently, if you do not define a constant whose value is zero, the enumeration will contain an illegal value when it is created.
If there is an obvious default case your application needs to represent, consider using an enumerated constant whose value is zero to represent the default. If there is no default case, consider using an enumerated constant whose value is zero that means the case that is not represented by any of the other enumerated constants.
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Do not define an enumeration value solely to mirror the state of the enumeration itself. For example, do not define an enumerated constant that merely marks the end of the enumeration. If you need to determine the last value of the enumeration, check for that value explicitly. In addition, you can perform a range check for the first and last enumerated constant if all values within the range are valid.
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Do not specify enumerated constants that are reserved for future use.
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When you define a method or property that takes an enumerated constant as a value, consider validating the value. The reason is that you can cast a numeric value to the enumeration type even if that numeric value is not defined in the enumeration.
The following example uses an enumeration to represent named values and another enumeration to represent named bit fields.
using System; public class Example { enum Days { Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday }; enum BoilingPoints { Celsius = 100, Fahrenheit = 212 }; [FlagsAttribute] enum Colors { Red = 1, Green = 2, Blue = 4, Yellow = 8 }; public static void Demo(System.Windows.Controls.TextBlock outputBlock) { Type weekdays = typeof(Days); outputBlock.Text += String.Format("The day of the week today is {0}.", Enum.Parse(weekdays, DateTime.Now.DayOfWeek.ToString(), false)); outputBlock.Text += "\n"; outputBlock.Text += "Enums can also represent some meaningful value. For example:" + "\n"; outputBlock.Text += String.Format("The BoilingPoints Enum defines the following items, and corresponding values:") + "\n"; outputBlock.Text += String.Format(" The boiling point in degrees {0:G} is {0:D}.", BoilingPoints.Celsius) + "\n"; outputBlock.Text += String.Format(" The boiling point in degrees {0:G} is {0:D}.", BoilingPoints.Fahrenheit) + "\n"; Colors myColors = Colors.Red | Colors.Blue | Colors.Yellow; outputBlock.Text += String.Format("myColors holds the following combination of colors: {0}", myColors) + "\n"; } }
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
How can these methods be substituted to achieve iteration throgh the values?
Substitutes for Enum.GetNames, Enum.GetValues
In the absence of the Enum.GetNames and Enum.GetValues methods, which are not supported in Silverlight, you can use reflection to iterate the public static fields of an enumeration type. Each field is represented by a FieldInfo object. Its Name property returns the name of the enumeration member. Its GetValue property returns the underlying value of the enumeration member.
This gives you a choice of how you want to create enumeration instances when you iterate the enumeration type's public static fields. You can retrieve their names and pass them to the Enum.Parse method. You can retrieve their values and pass them to the Enum.ToObject method. Or you can retrieve their values and cast them (in C#) or convert them (in Visual Basic) to enumeration values.
The following is some C# code that enumerates the fields of the DayOfWeek enumeration and instantiates DayOfWeek values in these three ways:
using System;
using System.Reflection;
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
DayOfWeek day = DayOfWeek.Sunday;
Type dayOfWeekType = day.GetType();
BindingFlags flags = BindingFlags.Static | BindingFlags.Public;
// Iterate the enumeration's public fields and instantiate enum values from names.
outputBlock.Text += "\nInstantiating Enum objects from their names:\n";
foreach (FieldInfo fld in dayOfWeekType.GetFields(flags))
{
// Get the name of the enumeration member.
string name = fld.Name;
// Use the name to instantiate an enum value.
DayOfWeek dow = (DayOfWeek) Enum.Parse(dayOfWeekType, name, true);
outputBlock.Text += String.Format("{0:F}: {0:d}\n", dow);
}
outputBlock.Text += "\nInstantiating Enum objects from their values:\n";
foreach (FieldInfo fld in dayOfWeekType.GetFields(flags))
{
// Get the value of the enumeration member and use it to instantiate an enum value.
DayOfWeek dow = (DayOfWeek) Enum.ToObject(dayOfWeekType, fld.GetValue(null));
outputBlock.Text += String.Format("{0:F}: {0:d}\n", dow);
}
outputBlock.Text += "\nUsing casting to instantiate Enum objects from their values:\n";
foreach (FieldInfo fld in dayOfWeekType.GetFields(flags))
{
// Get the value of the enumeration member and cast it to an enum value.
DayOfWeek dow = (DayOfWeek) fld.GetValue(null);
outputBlock.Text += String.Format("{0:F}: {0:d}\n", dow);
}
}
}
--Ron Petrusha
Common Language Runtime Developer Content
Microsoft Corporation
- 3/14/2011
- Uffe F
- 3/16/2011
- R Petrusha - MSFT
