How to convert numeric string object to nullable numeric

Question

With the following example, two calls are made to ConvertNumericStringObj, it sends back a Type int object both times.

string strValue = "123";
object obj = ConvertNumericStringObj(typeof(int), strValue);
object obj = ConvertNumericStringObj(typeof(int?), strValue);   

public static object ConvertNumericStringObj(Type conversion, object value)
{
    var t = conversion;
    if (t.IsGenericType && t.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
    {
        if (value == null)
        {
            return null;
        }
        t = Nullable.GetUnderlyingType(t);
    }
    return Convert.ChangeType(value, t);
}

My question is: Is there someway to pass in the string and int? Type and convert it so it returns a int? object?

Answer 1

If you want the types to potentially be either int or int? , then what you're looking for is "generics". This should get you what you want.

public static T ConvertNumericStringObj<T>(string value)
{
    var t = typeof (T);
    if (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>))
    {
        if (string.isNullOrEmpty(value))
            return default(T);

        t = Nullable.GetUnderlyingType(t);
    }
    return (T)Convert.ChangeType(value, t);
}

However , I'm curious why you wouldn't just return a nullable integer resulting from int.TryParse() instead.

public static int? ConvertNumericStringObj(string value)
{
    int? x;

    if (int.TryParse(value , out x)
        return x;

    return null;
}

Answer 2

Yes you can. Try Int32.TryParse .

public static int? ConvertNumericStringObj(string strValue)
{
    int x;
    if (Int32.TryParse(strValue , out x)
        return x;
    return null;
}

But I wonder, if you necessarily need to pass int? ?

Edit: as OP asked it to be a little generic, try extension method (roughly) like,

public static T? ConvertNumericStringObj<T>(string strValue) 
{
    if (string.IsNullOrEmpty(strValue))
        return null;
    return (T) Convert.ChangeType(strValue, typeof(T));
}

This way, you can then use as:

int? x = strX.ConvertNumericStringObj();