[Sample of Apr 5th] C# / VB Enum - String Converter
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Sample downloads
C# version: https://code.msdn.microsoft.com/CSEnumStringConverter-31cb7347
VB version: https://code.msdn.microsoft.com/VBEnumStringConverter-f1c3411c
Today’s code sample demonstrates how to convert enum to comma separated string & vice versa. It also covers the description attribute for enum while conversion.
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Introduction
This sample demonstrates how to convert enum to comma separated string & vice versa. It also covers the description attribute for enum while conversion.
Running the Code
The following steps walk through a demonstration of the enum-string convertion sample.
Step 1: Build and run the sample solution in Visual Studio 2010
Step 2: During first conversion process it will use the .NET framework built-in EnumConverter class to convert string to enum & back to string.
Step 3: During second conversion process it will use the EnumDescriptionConverter class to convert the description string to enum & back to string.
Implementation:
Following enum of ProgrammingLanguage has been used for example.
[Flags]
enum ProgrammingLanguage
{
[Description("Visual C#")]
CS = 0x1,
[Description("Visual Basic")]
VB = 0x2,
[Description("Visual C++")]
Cpp = 0x4,
[Description("Javascript")]
JS = 0x8,
// XAML
XAML = 0x10
}
System.ComponentModel.EnumConverter supports the conversion of one type to another which has been used in the first conversion process.
EnumConverter converter = new EnumConverter(typeof(ProgrammingLanguage));
// Convert string to enum.
string langStr = "CS, Cpp, XAML";
ProgrammingLanguage lang
= (ProgrammingLanguage)converter.ConvertFromString(langStr);
// Convert enum to string.
langStr = converter.ConvertToString(lang);
EnumDescriptionConverter class inherits EnumConverter to support Description attributes in the second conversion process.
1. It will split the comma separated string into string[] and then convert to long & do bitwise ORing to get the long value representing the enum value.
// convert from string to enum
public override object ConvertFrom(ITypeDescriptorContext context,
CultureInfo culture, object value)
{
if (value is string)
{
string strValue = (string)value;
if (strValue.IndexOf(enumSeperator) != -1)
{
ulong convertedValue = 0;
foreach (string v in strValue.Split(enumSeperator))
{
convertedValue |= Convert.ToUInt64(Parse(this.EnumType, v), culture);
}
return Enum.ToObject(this.EnumType, convertedValue);
}
else
{
return Parse(this.EnumType, strValue);
}
}
return base.ConvertFrom(context, culture, value);
}
2. It will read the custom attributes from the given enum, in this case Description attribute & prepare the corresponding string value. In case of flags enum, it will fetch Description attribute[] & prepare comma separated string as output.
// convert to string
public override object ConvertTo(ITypeDescriptorContext context,
CultureInfo culture, object value, Type destinationType)
{
if (destinationType == null)
{
throw new ArgumentNullException("destinationType");
}
if (destinationType == typeof(string) && value != null)
{
// Raise an argument exception if the value isn't defined and if
// the enum isn't a flags style.
//
Type underlyingType = Enum.GetUnderlyingType(this.EnumType);
if (value is IConvertible && value.GetType() != underlyingType)
{
value = ((IConvertible)value).ToType(underlyingType, culture);
}
if (!this.EnumType.IsDefined(typeof(FlagsAttribute), false) &&
!Enum.IsDefined(this.EnumType, value))
{
throw new ArgumentException(
String.Format("The value '{0}' is not a valid value for the enum '{1}'.",
value.ToString(), this.EnumType.Name));
}
// If the enum value is decorated with the Description attribute,
// return the Description value; otherwise return the name.
string enumName = Enum.Format(this.EnumType, value, "G");
string nameOrDesc;
if (enumName.IndexOf(enumSeperator) != -1)
{
// This is a flags enum. Split the descriptions with ', '.
bool firstTime = true;
StringBuilder retval = new StringBuilder();
foreach (string v in enumName.Split(enumSeperator))
{
nameOrDesc = v.Trim();
FieldInfo info = this.EnumType.GetField(nameOrDesc);
DescriptionAttribute[] attrs = (DescriptionAttribute[])
info.GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attrs.Length > 0)
{
nameOrDesc = attrs[0].Description;
}
if (firstTime)
{
retval.Append(nameOrDesc);
firstTime = false;
}
else
{
retval.Append(enumSeperator);
retval.Append(' ');
retval.Append(nameOrDesc);
}
}
return retval.ToString();
}
else
{
FieldInfo info = this.EnumType.GetField(enumName);
if (info != null)
{
DescriptionAttribute[] attrs = (DescriptionAttribute[])
info.GetCustomAttributes(typeof(DescriptionAttribute), false);
nameOrDesc = (attrs.Length > 0) ? attrs[0].Description : enumName;
}
else
{
nameOrDesc = enumName;
}
return nameOrDesc;
}
}
return base.ConvertTo(context, culture, value, destinationType);
}
More Information
EnumConverter Class
https://msdn.microsoft.com/en-us/library/system.componentmodel.enumconverter.aspx
DescriptionAttribute Members
https://msdn.microsoft.com/en-us/library/system.componentmodel.descriptionattribute_members(v=VS.85).aspx