如何将这些代码更改为C＃.net framework 3.5？

Question

Here is the code of .net framework 4.0. But our old system is using 3.5. It's difficult to upgrade all the codes. I want to know how to change the codes written by 4.0 to 3.5 codes.

The main problem is I don't know how to convert "return string.Join(",", states);" Error happened when I was trying to compile it using .net framework 3.5.

Thank you!

public enum States
{
....
}

public static string GetStates(uint stateFlags)
{
    var stateList = Enum.GetValues(typeof(States));
    var states = default(States);

    foreach (var state in stateList)
    {
        if (state == null) continue;
        var stateEnum = (States)state;
        if (HasState(stateFlags, stateEnum))
        {
            states = states | stateEnum;
        }
    }

    return string.Join(",", states);
}

The error is Error The best overloaded method match for 'string.Join(string, string[])' has some invalid arguments

Answer 1

string.Join in .Net 3.5 only supports a string array whereas .Net 4.0 has additional overloads to work with IEnumerable<string> or Object[] .

You should be passing a string[] to the Join method.

More at the MSDN docs:

.Net 4 : http://msdn.microsoft.com/en-us/library/dd992421(v=vs.100).aspx

.Net 3.5: http://msdn.microsoft.com/en-us/library/57a79xd0(v=vs.90).aspx

Answer 2

In .Net 3.5 the overload you used for "String.Join" is not available. Replace your return row with the following 2 rows:

 string[] stateNames = Enum.GetNames(typeof(States));
 return string.Join(",", stateNames);

The expected second argument is an array of Strings.

Answer 3

Here is a slightly modified version of your original solution

public enum States
{
    None = 0,
    StateOne = 1,
    StateTwo = 2,
    StateThree = 4,
    StateFour = 8,
};

public static string GetStates(uint stateFlags)
{
    var stateList = Enum.GetValues(typeof(States));
    List<States> states = new List<States>();

    foreach (int state in stateList)
    {        
        if ((stateFlags & state) != 0)
        {
            states.Add((States)state);
        }
    }

    return string.Join(",", states);
}

Running

GetStates((uint)(States.StateOne | States.StateTwo))

outputs

StateOne,StateTwo

Answer 4

Thank you everybody for your warmly help. I changed the last line to below:

        var valuesAsList = GetValues(states).Cast<string>().ToList();

        return string.Join(",", valuesAsList.ToArray());

And added the method:

    public static IEnumerable<Enum> GetValues(Enum enumeration)
    {
        List<Enum> enumerations = new List<Enum>();
        foreach (FieldInfo fieldInfo in enumeration.GetType().GetFields(BindingFlags.Static | BindingFlags.Public))
        {
            enumerations.Add((Enum)fieldInfo.GetValue(enumeration));
        }
        return enumerations;
    }

The compile error disappeared, but I still haven't test the code to see whether it's the same result with .net 4.0.

Thanks again.