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[Sample of Apr 5th] C# / VB Enum - String Converter

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C# version:
http://code.msdn.microsoft.com/CSEnumStringConverter-31cb7347
VB version: http://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
 http://msdn.microsoft.com/en-us/library/system.componentmodel.enumconverter.aspx
 
DescriptionAttribute Members
 http://msdn.microsoft.com/en-us/library/system.componentmodel.descriptionattribute_members(v=VS.85).aspx

Leave a Comment
  • Please add 1 and 4 and type the answer here:
  • Post
  • ...doesn't support localizations as far as I can tell.

  • useful for some WMI classes i am often using ( Win32_ComputerSystem and Win32_OperatingSystem )

    Is there any minimum version for .Net Framework ? In the article, you are seaking about VS 2010, but is it working with my old VS 2008 Standard ? ( i will try to-morrow )

  • 感谢Mr.Ge

  • good

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