Convert a string containing a hexadecimal value starting with "0x" to an integer or long

int value = (int)new System.ComponentModel.Int32Converter().ConvertFromString("0x310530");

From MSDN:

NumberStyles.AllowHexSpecifier

Indicates that the numeric string represents a hexadecimal value. Valid hexadecimal values include the numeric digits 0-9 and the hexadecimal digits A-F and a-f. Strings that are parsed using this style cannot be prefixed with "0x" or "&h".

So you have to strip out the 0x prefix first:

string s = "0x310530";
int result;

if (s != null && s.StartsWith("0x") && int.TryParse(s.Substring(2),
                                                    NumberStyles.AllowHexSpecifier,
                                                    null,
                                                    out result))
{
    // result == 3212592
}

Direct from SHanselman, as pointed by Cristi Diaconescu, but I've included the main source code:

public static T GetTfromString<T>(string mystring)
{
   var foo = TypeDescriptor.GetConverter(typeof(T));
   return (T)(foo.ConvertFromInvariantString(mystring));
}

The whole article deserves a closer look!