/// <summary>
/// Gets Expression for Enum to string conversion.
/// </summary>
/// <typeparam name="TEnum">Enum type. May be nullable.</typeparam>
/// <param name="toString">Enum to string conversion delegate.</param>
/// <param name="nullEnumString">String for null enum value.</param>
/// <param name="zeroEnumString">String for 0 enum value.</param>
/// <param name="delimiter">Delimiter for [Flags] enum.</param>
/// <returns></returns>
public static Expression <Func <TEnum, string> > GetEnumToStringExpression <TEnum>(Func <Enum, string> toString, string nullEnumString = null, string zeroEnumString = "", string delimiter = ", ")
{
Type enumType = typeof(TEnum);
Type enumExactType = enumType;
Type nullableEnumType = Nullable.GetUnderlyingType(enumExactType);
if (nullableEnumType != null)
{
enumExactType = nullableEnumType;
}
Type enumUnderlyingType = Enum.GetUnderlyingType(enumExactType);
var allMembers = EnumExtensions.GetAllMembers(enumExactType)
.Select(e => new KeyValuePair <Enum, string>(e, toString(e)))
.OrderBy(e => e.Value)
.ToDictionary(e => e.Key, e => e.Value);
object zero = Activator.CreateInstance(enumUnderlyingType);
Enum zeroEnumVal = (Enum)Enum.ToObject(enumExactType, zero);
Expression zeroStringExpression;
if (zeroEnumString == "")
{
string zeroString;
if (allMembers.TryGetValue(zeroEnumVal, out zeroString))
{
allMembers.Remove(zeroEnumVal);
zeroStringExpression = Expression.Constant(zeroString, StringType);
}
else
{
zeroStringExpression = EmptyStringExpression;
}
}
else
{
if (allMembers.ContainsKey(zeroEnumVal))
{
allMembers.Remove(zeroEnumVal);
}
zeroStringExpression = Expression.Constant(zeroEnumString, StringType);
}
Expression zeroConstant = Expression.Constant(zeroEnumVal, enumType);//Expression.Convert(Expression.Constant(zero, enumUnderlyingType), enumType);
Expression nullStringExpression = nullEnumString == null ? NullStringExpression : Expression.Constant(nullEnumString, StringType);
//Flag enum.
if (enumExactType.GetCustomAttributes(typeof(FlagsAttribute), false).Length != 0)
{
return(GetFlagEnumToStringExpression <TEnum>(allMembers, enumType, enumExactType, enumUnderlyingType, zeroConstant, zeroStringExpression, nullStringExpression, delimiter));
}
else
{
return(GetEnumToStringExpression <TEnum>(allMembers, enumType, enumExactType, zeroConstant, zeroStringExpression, nullStringExpression));
}
}