Question

In the stub below how do I pass in (MyEnum) as a parameter such that I can use this procedure with any enum?

public static Enum Proc(this Enum e)
{
Int32 i = (Int32)(MyEnum)e;
...

Here is the solution I have come up with that works:

public static Enum Next(this Enum e, Type eT)
{
  Int32 i = (Int32)(Object)e;   
  return (Enum)Enum.Parse(eT, Enum.GetName(eT, Enum.GetName(eT, ++i) == null? i = 0 : i));  
}

This solution isn’t ideal because I have to do this to get the next value:

MyEnum e = (MyEnum)e.Next(typeof(MyEnum));

I’d rather just do

MyEnum e = e.Next(typeof(MyEnum));

Or even better:

MyEnum e = e.Next();

Anyone who can provide the simple solution can have the point.

Also the code I’ve written above runs fine in LinqPad but only compiles in WP7 and then throws an exception when I run it (InvalidProgramException).

Answer 1

Here’s a function that will cycle through the values of any enum:

static public Enum Cycle(this Enum e)
{
    bool found = false;
    Enum first = null;
    foreach (Enum i in Enum.GetValues(e.GetType()))
    {
        if (first == null)
            first = i;
        if (found)
            return i;
        found = e.Equals(i);
    }
    if (found)
        return first;
    return null;
}

For versions of C# that don’t have Enum.GetValues, you’ll have to use a method like this which only works for enums whose values start at 0 and increment by 1:

static public Enum Cycle(this Enum e)
{
    var i = ((IConvertible)e).ToInt64(null) + 1;
    var eT = e.GetType();
    var next = Enum.GetName(eT, i);
    return (Enum)Enum.Parse(eT, next ?? Enum.GetName(eT, 0), false);
}

Use it like:

var nextEnum = (MyEnum)curEnum.Cycle();